Scorpions, Other Arachnids, Millipedes, Centipedes

Millipede with Two Pair of Legs on Most Segments.

Cylindrical and Flattened Millipedes. Left Image Courtesy of Detagalli, Right Framco Folini.

The name millipede is a compound word formed from the Latin roots milli ("thousand") and ped ("foot"). Despite their name, millipedes do not have 1,000 legs, although the rare species Illacme plenipes has up to 750. Common species have between 36 and 400 legs. The class contains around 10,000 species in 13 orders and 115 families. The giant African millipede (Archispirostreptus gigas), known as shongololos, is the largest species of millipede. They range from 0.079 to 11 inches in length, and can have as few as eleven, to over a hundred segments. They are generally black or brown in color, although there are few brightly colored species.

A 12-inch millipede from South Africa. Totally harmless to humans.

Most millipedes eat decaying leaves and other dead plant matter, moisturizing the food with secretions and then scraping it in with the jaws. However, they can also be a minor garden pest, especially in greenhouses where they can cause severe damage to emergent seedlings. Signs of their damage include the stripping of the outer layers of a young plant stem and irregular damage to leaves.

Millipedes can be easily distinguished from the somewhat similar and related centipedes (Class Chilopoda), which move rapidly, and have a single pair of legs for each body segment. However, unlike centipedes, millipedes are by nature not predators, and due to their slow, non-aggressive behavior and simple diet of decomposing leaves, are easy to keep and ideal as pets. As a rule arthropods that move slowly are plant feeders and predators are fast moving. It makes biological sense -you do not need to be fast to run down a leaf.

This class of arthropod is thought to be among the first animals to have colonized land during the Silurian geologic period. These early forms probably ate mosses and other primitive plants. The oldest known land creature, Pneumodesmus newmani, was a 0.39 inch long millipede, and lived 428 million years ago.

The millipede’s most obvious feature is its large number of legs making them rather slow, but they are powerful burrowers. With their legs and body length moving in a wavelike pattern, they easily force their way underground head first. They also seem to have some engineering ability, reinforcing the tunnel by rearranging the particles around it.

Male millipedes can be differentiated from female millipedes by the presence of one or two pairs of legs modified into gonopods. These modified legs, which are usually on the seventh segment, are used to transfer sperm packets to the female during copulation. A few species are parthenogenetic, having few, if any, males. The genital openings are located on the third segment, and are accompanied in the male by one or two penises, which deposit the sperm packets onto the gonopods. In the female, the genital pores open into a small chamber, or vulva, which is covered by a small hood-like cover, and is used to store the sperm after copulation. Females lay between ten and three hundred eggs at a time, depending on species, fertilizing them with the stored sperm as they do so. Many species simply deposit the eggs on moist soil or organic detritus, but some construct nests lined with dried feces.

Mating Millipedes. Image Courtesy of

The young hatch after a few weeks, and typically have only three pairs of legs, followed by up to four legless segments. As they grow, they continually molt, adding further segments and legs as they do so. Some species molt within specially prepared chambers, which they may also use to wait out dry weather, and most species eat the shed exoskeleton after molting. Millipedes live from one to ten years, depending on species.

Due to their lack of speed and their inability to bite or sting, millipedes’ primary defense mechanism is to curl into a tight coil - protecting their delicate legs inside an armored body exterior. Many species also emit poisonous liquid secretions or hydrogen cyanide gas through microscopic pores along the sides of their bodies as a secondary defense. Some of these substances are caustic and can burn the exoskeleton of ants and other insect predators, and the skin and eyes of larger predators. Animals such as Capuchin monkeys have been observed intentionally irritating millipedes in order to rub the chemicals on themselves to repel mosquitoes. At least one species, Polyxenus fasciculatus employs detachable bristles to entangle ants.

Coiled Millipede in Defensive Position.

As far as humans are concerned, this chemical brew is fairly harmless, usually causing only minor effects on the skin, the main effect being discoloration, but other effects may also include pain, itching, local erythema, edema, blisters, eczema, and occasionally cracked skin. Eye exposures to these secretions causes general eye irritation and potentially more severe effects such as conjunctivitis. First aid consists of flushing the area thoroughly with water; further treatment is aimed at relieving the local effects. An insect dealer at one of our insect fairs was recently observing a small black tropical species of millipede (about 4 inches in length) when it shot a spray of some unknown chemical from a distance of over 2 feet directly into his eye. The result was quite painful and resulted in considerable swelling.

Result (2 days later) From a Millipede Spraying a Chemical into the Eyes of an Insect Dealer.

Sometimes millipedes, occasionally accompanied by centipedes and sow bugs, will migrate in great numbers. This is believed to be the result of a heavy buildup because of extremely favorable environmental conditions followed by drought. Migrations at times have been so heavy as to make it necessary to sprinkle sand on slippery railroad tracks to provide traction for the driving wheels of the trains. In one migration a farmer shoveled several gallons of these critters a day from his front porch for 3 weeks.

Centipedes-Class Chilopada

Centipedes (from Latin prefix centi-, "hundred", and Latin pes, pedis, "foot") are arthropods belonging to the class Chilopoda and the Subphylum Myriapoda. They are elongated animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. All centipedes always have an odd number of pairs of legs, e.g. 15 or 17 pairs of legs (30 or 34 legs) but never 16 pairs (32 legs). A diagnostic characteristic of this group is a pair of venom claws or that are held on the underside of the head and formed from a modified first pair of legs.

The effect of the bite from these arthropods depends primarily on the size of the centipedes. Most centipedes in the US are relatively small, rarely exceed a few inches in length, and are of no danger to humans. However, around the world there are a number of species, including some in the United States, that in some cases exceeds a foot in length. In the US, species of this size can be found in the southwest from Arizona to Texas and also in the island state of Hawaii.

Although not considered deadly to humans, the bite from these larger centipedes can be quite painful. The authors are aware of a few individuals who have been bitten by the larger Arizona species resulting in considerable swelling and pain. We recently documented a case where a man in Arizona took a break from his yard work to take a drink of water from a hose. Unfortunately, a 10-inch centipede had taken refuge there. The critter bit him on the tongue and the pain, substantial swelling and debilitation lasted for several days.

It has been reported that some centipedes are capable of pinching with the claws on their legs. We were once dealing with a Thai insect dealer and noticed a double row of pits in his arm. He indicated that he woke up one night with a large centipede on his arm that pinched with its claws and injected venom before it could be removed. In Southeast Asia some centipedes exceed 15 inches in length and are greatly feared by the general public as well as the commercial insect collectors.

Modified First Pair of Legs or Poison Fangs.

They normally have a drab coloration combining shades of brown and red; however, many of the larger tropical species are brightly colored. Generally speaking bright colors in arthropods are considered as sign of danger “e.g. don’t mess with me-I am bad). Size can range from a few millimeters in the smaller species to 12 or more inches species. Worldwide there are estimated to be 8,000 species with about 3,000 described species. Centipedes are found in an array of terrestrial habitats from tropical rainforests to deserts. Within these habitats they require a moist micro-habitat due to the lack the waxy cuticle of insects and arachnids which functions to reduce water loss from the body. Accordingly, they are found in soil and leaf litter, under stones and deadwood, and inside logs.

Centipedes possess a variable number of ocelli (simple eyes), which are sometimes clustered together to form true compound eyes. Even so, it appears that centipedes are only capable of discerning light and dark, and not of true vision. Indeed, many species lack eyes altogether. In some species the final pair of legs acts as sense organs similar to antennae, but facing backwards. An unusual sense organ found in some groups is the organs of Tömösvary. These are located at the base of the antennae, and consist of a disc-like structure with a central pore surrounded by sensory cells. They are probably used for sensing vibrations, and may even provide a sense of hearing.

Behind the head, the body consists of fifteen or more segments. Most of the segments bear a single pair of legs. Each pair of legs is slightly longer than the pair immediately in front of it, ensuring that they do not overlap, and therefore reducing the chance that they will collide with each other while moving swiftly. In extreme cases, the last pair of legs may be twice the length of the first pair. The final segment bears a telson and includes the openings of the reproductive organs.

Centipedes are predators, and mainly use their antennae to seek out their prey. The digestive tract forms a simple tube, with digestive glands attached to the mouthparts. Like insects, centipedes breathe through a tracheal system, typically with a single opening, or spiracle on each body segment.

As with scorpions and some of the other arthropods males externally deposit a spermatophore which the females seek and incorporate into her genitalia. In some species the spermatophore is deposited in a web, and the male undertakes a courtship dance to encourage the female to engulf his sperm. In other cases, the males just leave them for the females to find. In temperate areas egg laying occurs in spring and summer but in subtropical and tropical areas there appears to be little seasonality to centipede breeding. It is also notable that there are a few known species of parthenogenetic centipedes.

The number of eggs per female ranges from about 10 to 50. Time of development to hatching is highly variable and may take from one to a few months. Similarly the length of development of the life cycle is variable depending of the species and prevailing temperature. For example, it can take 3 years for the larger tropical species to reach adulthood, whereas under the right conditions smaller species may reach a reproductive period in 1 year. In addition, centipedes are relatively long-lived when compared to insects with some species living 5 to 6 years. Some species exhibit parental care, the eggs 15 to 60 in number are laid in a nest in the soil or in rotten wood with the female remaining with the eggs, guarding and licking them to protect them from fungi. The female in some species stays with the young after they have hatched, guarding them until they are ready to leave. If disturbed the females tend to either abandon the eggs of their young or eat them; abandoned eggs tend to fall prey to fungi rapidly. Some species are matriphagic, meaning that the offspring eat their mother.

Female Guarding Eggs. Image Courtesy Marshal Hedin.

Some species of centipede can be hazardous to humans because of their bite. Although a bite to an adult human is usually very painful and may cause severe swelling, chills, fever, and weakness, it is unlikely to be fatal. Bites can be dangerous to small children and those with allergies to bee stings. The bite of larger centipedes can induce anaphylactic shock in such people. Smaller centipedes usually do not puncture human skin.

There are several orders within this class.

Scutigeromorpha. This order possess up to 15 leg-bearing segments. They are very fast creatures with top speeds of up to 15 body-lengths per second. They are the only centipede with compound eyes. They possess long and multisegmented antennae. Adaption to a burrowing life-style has led to the degeneration of compound eyes in other orders.

Lithobiomorpha. This group has lost the compound eyes, and sometimes has no eyes altogether. Instead, its eyes have facets or groups of facets. Its spiracles are paired and can be found laterally. Every leg-bearing segment of this organism has a separate tergite. It also has relatively short antennae and legs.

Craterostigmomorpha. These are the least diverse comprising only two species. Their geographic range is restricted to Tasmania and New Zealand.

Scolopendromorpha. The Scolopendromorpha comprise 21 or more segments with the same number of paired legs. Their antennae have 17 or more segments. Their eyes will have at least 4 facets on each side. This order contains some of the larger tropical species.

Geophilomorpha. The Geophilomorpha are the most derived group of centipedes, and bear upwards of 27 leg-bearing segments. They are without fail eyeless and blind. They also have 14 segmented antennae.

Species of Interest:

Scolopendra gigantea (also known as Peruvian giant yellow-leg centipede and Amazonian giant centipede) is the largest representative of the genus Scolopendra, regularly reaching lengths of 12 inches. It inhabits the northern and western regions of South America and the islands of Trinidad, Jamaica, and Hispaniola. It is carnivorous, feeding on lizards, frogs, birds, mice, and even bats. It is also known to prey on tarantulas. The body consists of 21 to 23 segments which are coppery red or maroon in color, each with a pair of yellow-tinted legs; the legs are adapted for fast walking. The bite contains extremely potent venom, containing acetylcholine, histamine and serotonin (pain mediators), proteases and a cardio-depressant factor. It is toxic to humans and causes severe swelling, chills, fever, and weakness. However, although bites are painful, they are very unlikely to be fatal to humans. . However, as indicated this powerful beast hunts bats. It frequently can be seen crawling over cave ceilings. It will typically pass up smaller prey such as cockroaches on it way. Once seize with its venomous poison jaws the bats are said to die in as little as 30 seconds. Although probably not capable of killing a human, villagers in Venezuela claim that the bite of one did kill a child.

S. gigantea is a popular pet among arthropod enthusiasts, but must be handled with protective equipment, as even a trace of the venom coming in contact with skin can cause a reaction. Female S. gigantea centipedes exhibit parental care, guarding and tending their nests of eggs. Juveniles are very dark-red or black in color, and very thin with large spherical red heads. They molt several times before reaching adult size.

Peruvian Giant Yellow-leg Centipede. Left Image Courtesy John Hill. Right Courtesy of Tod Baker.

Scolopendra polymorpha, the common desert centipede or Sonoran Desert centipede, is indigenous to the Southwestern United States and Northern Mexico, up to the Pacific coast. It inhabits dry grasslands, forest and desert; in these habitats the centipedes will generally take up residence under rocks, though they have been observed creating burrows in suitable environments and inside rotting logs. Its body generally reaches 4-7 inches (10-18 cm) in length. Coloration is variable, hence the species name"polymorpha" which means "many forms", and alternate common names like "multi-colored centipede". The body segments have one dark lateral stripe, accordingly the names tiger centipede or tiger-stripe centipede. Generally this species has a darker brown, red, or orange colored head and lighter brown, tan, or orange body segments with yellow legs. Its antennae have 7 or more smooth segments.

Sonoran Desert Centipede. Image Courtesy Matt Reinbold.

Vietnamese Centipede. Scolopendra subspinipes. This is a species of centipede occasionally reaching 19 cm in length. . It is found throughout tropical and subtropical regions of the world, and is one of only three species of centipedes in Hawaii [2]. It is dark in color and has 21 body segments. It has one pair of legs per segment, a characteristic of centipedes. It is often sold as a terrarium animal and called the Vietnamese Centipede. The female protects her eggs until they hatch. The centipedes molt once each year, and take three to four years to attain full adult size. They may live for 10 years or more. It generally feeds by grasping its prey with a pair of legs and injecting venom with its front legs, which are modified for this purpose. The venom of Scolopendra subspinipes can cause pain and serious swelling in humans.

Vietnamese Centipede.

Common House Centipede. Scutigera coleoptrata, (one of several species commonly known as the house centipede), is a typically yellowish-grey centipede with 15 pairs of legs. Originally endemic to the Mediterranean region, the species has spread to other parts of the world, where it usually lives in human homes. It is also known as a "mustache bug" in certain cultures and in many places of America is (mistakenly) referred to as silverfish.

It is (1 inch) in length and has up to 15 pairs of remarkably long legs. These delicate legs are attached to a rigid body. This enables it to reach surprising speeds of up to 0.4 meters per second (1.3 ft/s) running across floors, up walls and along ceilings. Its body is yellowish-grey and has three dark-colored dorsal stripes running down its length; the legs also have dark stripes. Unlike most other centipedes, house centipedes and their close relatives have well-developed, faceted eyes. S. coleoptrata has developed auto-mimicry in that its hind legs present the appearance of antennae. When at rest, it is not easy to tell its front from its back. They live anywhere from three to seven years, depending on the environment. They can start breeding in their third year. House centipedes feed on spiders, bedbugs, termites, cockroaches, silverfish, ants and other household arthropods. Although capable of biting they pose no threat to humans.

The common house centipede, as the name implies, is a species that can be found indoors. It could be considered beneficial as it eats many common household pests such as spiders and cockroaches; however, most homeowners have a difficult time accepting the possibility that something so gruesome looking could actually be beneficial.

Common House Centipede.

Scolopendra spp. There are a number of species in this order most of which are the largest of centipedes.

Scolependra species.

At times it almost appears that these and other arthropods have the ability to think. Of course this is quite doubtful, but they have been well equipped to react instinctively (almost appearing intelligently) too many circumstances. We recently watched a large Vietnamese centipede catch and feed on a cricket. Once caught the centipede immediately cut off the cricket’s legs thus removing its ability to escape. Thinking that this was an accident we fed it another cricket with the same results. Taking this impromptu experiment a step further we fed a cricket to a different centipede with the same result.

The authors recently documented the case of a bite from a large species of Arizona centipede. In this situation, a homeowner bent over to drink from a water hose. Unfortunately, a 12-inch centipede had recently occupied the hose and, when the water was turned on the centipede appeared and bit the individual on the tongue. His tongue and mouth swelled considerably and he was in pain for several days.

With the exception of the common house centipede, centipedes are not as commonly found in the home as millipedes and, when encountered, never in the numbers that can occur with millipedes. Of course part of the reason for this is that their outdoor populations never reach that of millipedes. However, if a centipede does occur indoors it can be somewhat stressful. One evening (on a Hawaiian trip) one of our visitors was washing dishes and a seven inch centipede appeared from under the dishwashers (apparently a fairly common occurrence in Hawaii). She came running from the kitchen screaming centipede, centipede! According to her she couldn’t sleep that night. A note of importance! Never try to transport living centipedes on a commercial airline. After capturing the centipede I decided it would make a nice addition to our insect zoo at Cal Poly. I neatly packed it away in a small container in my luggage. Of course on getting home the critter was dead. I guess it gets pretty cold in the cargo part of the plane.

On a later occasion I decided to bring back several giant millipedes (12-inch beauties) I had collected in Malaysia. Keeping in mind that they wouldn’t make it in the cargo area I decided to carry them in my carry-on luggage. While waiting for the plane to begin loading I decided to check and see how they were doing-big mistake! One of the stewardesses saw them out of the corner of her eye and freaked. She first thought they were snakes and called security. After convincing all involved that they weren’t snakes, I still couldn’t convince anyone that they were harmless. I was subsequently escorted from the airport to release the monsters back into nature-almost missed that flight. I guess it could have been worse. Luckily for us, the movie “Snakes on a Plane” had not yet been released.

Not learning from those experiences I later transported a large variety of living critters (scorpions, walking sticks, millipedes, tarantulas, etc.) on Alaskan Airlines up to Oregon for a presentation I was giving to the Oregon Pest Control Association. I had no problem getting them on the plane on the way up, but was stopped by security on the way back. Major alert-you would have thought I was some kind of terrorist. After convincing the authorities that these critters were not going to kill anyone and that I wasn’t totally nuts, the additional problem was that it is prohibitive to bring living animals of any kind on a plane. I think the exceptions were dogs and cats in cargo and goldfish. They again wanted me to take the specimen out of the airport and release them. After some fast taking and actually doing a short presentation on these arthropods to the airline officials, they let me put them in cargo after they triple boxed them. Again, we almost missed that flight as well.

We once stopped at a roadside stand in Thailand to buy some dried-roasted caterpillars for an afternoon snack (when in Rome do as the Romans) and were offered a quart bottle of home-brewed whiskey; but instead of having a worm in the bottle, as does Mexican tequila, there was a 14-inch pickled centipede. Drinking the whiskey enhanced by centipede was said to give the consumer great strength (or at least make the consumer think he had great strength until he sobered up). This belief is apparently common in several of the South-East Asian countries. By the way, the worm in the bottom of the tequila bottle is a caterpillar that feeds on the century plant from which tequila is derived.

Arachnids-Class Arachnida

The arachnids can be separated from other classes of the arthropods by the presence of 8 legs and the fact that the head and thorax are combined into one unit referred to as a cephalothorax. The first pair of appendages behind the mouth is called chelicerae and is basically the mouthparts. The second pair of appendages behind the mouth is the pedipalps. Both the chelicerae and pedipalps differ in structure depending on the type of arachnid. For example, in scorpions the pedipalps are pincher like and in spiders the chelicerae are fanglike.

Sun Spiders, Wind Scorpions, Order Solpugida, Solifugae

The sun spiders or wind scorpions have large chelicerae or jaws that occupy almost the entire front half of the cephalothorax. The bite of these arachnids is purely mechanical with no venom. This makes perfect biological sense. If a predatory arthropod such as a sun spider has huge chelicerae that are used mainly to subdue its prey, there is little need for venom. They are moderate to large arachnids, with the larger species approaching 3 inches in length. They have long pedipalps, which function as sense organs similar to insects’ antennae and give the appearance of an extra pair of legs. The pedipalps terminate in eversible adhesive organs, which are used to capture flying prey and for climbing. They stridulate with their chelicerae, resulting in a rattling noise.

A sunspider. Image Courtesy of

This order contains more than 1,000 described species in about 140 genera. The name derives from Latin, and means those that flee from the sun. Their common names include camel spider, wind scorpion, jerrymuglum, sun scorpion and sun spider. In southern Africa they are known by a host of names including red romans, haarskeerders and baardskeerders, the latter two relating to the belief they use their formidable jaws to clip hair from humans and animals to line their subterranean nests. Most species inhabit warm and arid habitats, including virtually all deserts in both the Eastern and Western Hemispheres, excluding Australia.

They are carnivorous or omnivorous, with most species feeding on termites, darkling beetles, and other small ground-dwelling arthropods. They are opportunistic feeders and have been recorded as feeding on snakes, small lizards and rodents. Prey is located with the pedipalps and killed and cut into pieces by the chelicerae. Although they do not normally attack humans, these chelicerae can penetrate human skin, and painful bites have been reported with little if any symptoms following the initial attack.

Reproduction can involve direct or indirect sperm transfer; when indirect; the male emits a spermatophore on the ground and then inserts it with his chelicerae in the female’s genital pore: To do this, he flings the female on her back. The female then digs a burrow, into which she lays 50 to 200 eggs, depending on the species: she guards them until they hatch. Because the female will not feed during this time, she will try to fatten herself beforehand, and a species of 2 inches has been observed to eat more than 100 flies during that time in the laboratory.

Solifugae are the subject of many urban legends and exaggerations about their size, speed, behavior, appetite and lethality. They are not especially large, the biggest having a leg span of perhaps 12 centimeters (5 in). They are fast on land compared to other invertebrates; the fastest can run approaching10 mph, nearly half as fast as the fastest human sprinter. Members of this order of Arachnida apparently have no venom, with the possible exception of one species in India and do not spin webs.

In the Middle East, it is widely rumored among American and coalition military forces stationed there that Solifugae will feed on living human flesh. The story goes that the creature will inject some anaesthetizing venom into the exposed skin of its sleeping victim, then feed voraciously, leaving the victim to awaken with a gaping wound. Solifugae, however, do not produce such an anesthetic, and they do not attack prey larger than themselves unless threatened.

While the absence of venom in Solifugae was long thought a fact, there is a single published study of one species, Rhagodes nigrocinctus, carried out in India in 1978 by a pair of researchers who did histological preparations of the chelicerae, and found what they believed to be epidermal glands Extracts from these glands were then injected into lizards, where it induced paralysis in 7 of 10 tests. While this study has never been confirmed, and while other researchers have been unable to locate similar glands in other species, this particular species does appear to possess venom, although it is not known if there is any mechanism for introducing it into prey (recall that the researchers manually injected it into lizards).

There are a number of camel spider stories that have recently spread on the internet. These began to appear during the 1990-91 Gulf War and have now reemerged and become even more widespread with the return of U.S. troops to Iraq. Almost everything on the web (emerging from Iraq) about the size, ferocity and danger of these arthropods is untrue. Some of the fallacies are listed below:

1. Camel spiders can move at speeds over 30 MPH, screaming while they run.

2. Camel spiders can be as large as a Frisbee.

3. Camel spider venom is an anesthetic that numbs their prey.

4. Camel spiders can jump three feet high.

5. Camel spiders get their name because they crawl into the stomach of camels and eat them.

The common camel spider in Iraq is somewhat larger than the species in southwestern US (approximately three inches in length). The picture commonly found on the web is a gross exaggeration of this species. They pose no danger to the troops or camels although there have been a few bites which are basically small puncture wounds with no venom. These bites commonly come from the troops attempting to fight these with true scorpions. For some reason most of the troops that fight camel spiders and scorpions come for the Deep South of the US. They don’t jump (the camel spiders not the troops) and can possibly run a short distance at a speed of a mile or two an hour. And of course they don’t eat camel stomach.

A camel spider from Iraq. Size is greatly exaggerated (really about three inches) by angle of camera.

Vinegaroons or Whiptail Scorpions-Order-Uropygi

Vinegaroons or whiptailed scorpions are nocturnal predators that in the United States range in distribution from Arizona into Texas. They are as found in many tropical areas of the world. The Arizona species Mastigoproctus giganteus is the largest species in the world with adults approaching 3-inches in length. These arachnids are characterized by chelate chelicerae (pincher like) that are used to cut up food, a pair of heavily armored pedipalps that are used to capture their prey, a first pair of legs that are “feeler like” and an elongate tail, or whip like structure, arising from the tip of the abdomen. As their name indicates vinegaroons are capable of squirting vinegar or acetic acid from the tip of the whip when disturbed. These bizarre arthropods present no hazard to humans and actually make excellent pets if you’re into keeping bugs. One fallacy associated with them is that if a person were to get bitten by a vinegaroon he or she would taste vinegar for a given period of time. This is absolutely not true. Actually, when kept as a pet, they are very handy and can be shaken over a dinner salad with a little oil to make a tasty vinegar-and-oil salad dressing!

A tunnel of a carpenter bee with developing larva and pupa. Image courtesy of VoPak Inc.

Scorpions-Order Scorpionida

Scorpions.Scorpions are well known animals that range in distribution as far north as Canada and as far south as the southern tip of South America. These creatures are hardy and can survive in extreme conditions, including temperatures as high as 115 F, being frozen solid for weeks, total submersion in water for up to 48 hours, irradiation levels many times the lethal limit to humans and lack of food for up to one year. These are amongst the oldest ancestral arthropods, having crawled from the oceans for a terrestrial way of life over 350 million years ago. Because scorpions are greatly feared by many humans, one can only imagine if these, ancestral monsters existed today. Imagine the extreme reaction to encountering one of these three foot long scorpions! Scorpion chelicerae are used to cut and chew food while the pedipalps are pincher-like, or chelate, and used to subdue and hold the prey during feeding.

The cephalothorax bears one pair of eyes near the midline and several along the lateral margins on each side allowing a scorpion to see in all directions at any one time. These eyes are comparatively simple and do not produce precise images. However they are very sensitive to minor differences in brightness and therefore movements. As a result it is very difficult to approach a scorpion without being detected. It might be expected that these sensitive eyes might be dazzled or even harmed by bright sunlight; however, the scorpion has a solution to that, namely sunglasses if you will. Its eyes contain pigments that migrate toward the surface when exposed to sunlight forming a protective screening barrier. With reduction in light the pigments merely drain to the lower areas of the eye.

The abdomen terminates in a five segmented tail-like structure with a bulbous stinger at the tip. The tip of the stinger is very sharp and quite strong (one fourth of its composition is metal including iron, zinc and manganese). Males can be distinguished from females by their larger pair of comb-like structures (pectins), which are located on the underside of the cephalothorax. The function of pectins is unknown but they are thought to be used both for detecting food and smelling the presence of the opposite sex.

Comb-like pectins on underside of scorpion.

These creatures have a unique method of locating their prey which consists of any living animal their size or smaller, including insects, other scorpions and arachnids, birds and small mammals. Because they are nocturnal and do not have well-developed eyes, vision is of little use for this activity. Instead, their legs are equipped with many fine erect hairs that are extremely sensitive to the movement of an approaching prey. When a beetle or any other prey approaches a scorpion, its movement sends out two types of waves across the ground; one type is fast moving and the other is slow. A hungry scorpion stands with its legs spread in an almost circular configuration. With their legs essentially pointing in all possible directions, they can easily detect the direction of a potential prey by detecting which leg is disturbed first by the fast moving wave pulses. The distance of the prey from the scorpion is computed by using the difference in time it takes the fast moving waves and slow moving waves to reach the scorpion’s leg. The authors have no idea how a scorpion uses wave mechanics or the laws of physics to find their prey, but insects and their relatives are nothing more than small computers that have been programmed by nature.

When scorpions are placed under ultraviolet light (e.g. a blacklight), they glow. However, a glow will only be produced in adult specimens as the substances in the skin required to produce the glow are not found in adolescents.

The reason for this is due to certain structures in their exoskeleton that reflect ultraviolet light. The exact reason for this phenomenon is not known; however, we also do not know exactly how or what scorpions see at night. It would make perfect biological sense that scorpions might be able to see ultraviolet wave lengths and this is another possible means of finding a mate in the dark of night. Also many plants emit or reflect ultraviolet light and, in doing so, attract pollinators, which are often insects (e.g. bees, flies and beetles). Many other insects are positively phototrophic (attracted to light) and are even more attracted to ultraviolet light than other light wave lengths. This is well illustrated by the fact that entomologists use ultra violet lights to attract insects when night collecting. Of course all this adds up to the distinct probability that scorpions reflect ultra-violet light in order to attract insects, their main source of food.

Two scorpions (one eating the other) viewed under ultraviolet light. Image compliments of Bob Spencer.

Scorpions exhibit external reproduction. When a female scorpion is ready to mate, she will deposit a chemical or sex pheromone on the ground. She normally does not travel far from this release. Any male of the same species happening to venture over this chemical, will sense its presence by olfactory receptors located on the pectins. At this point the male instinctively realizes that a female is nearby and that she is receptive for mating. Subsequently mating drive kicks in and he exhibits a rather violent series of jerky movements that scorpion experts have named juddering. His lurching sends seismic waves across the sand, which in turn are perceived by the female. The waves alert her to his presence and indicate that he is receptive to mating. Typically the male will then choose a flat surface to attach a sperm packet that is located on an elongated stalk. He subsequently goes through a series of mating movements to attract a female. Mating can get a little rough at this point. It is not uncommon for the male or female or both to club (not sting) each other with their tail (stinger). The male is some species will actually sting the female in the soft joint between the opposing claws of her pincher. This obviously does not kill the female but apparently tend to tranquilize her to point where she is less combative and more receptive. It is well documented that scorpions are relatively immune to the venom of their species. Mating terminates in his grasping her pedipalps and dragging his mate over the stalked spermatophore.

Once mated, it generally takes a year before the female gives live birth to a dozen or more young. Typically the young scorpions crawl up on the back of the mother until the first molt. If the young scorpions are removed from the mother’s back prior to their first molt they will typically die due to the lack of sufficient moisture. Apparently the mother secrets a liquid that prevents dehydrating. It is not uncommon to purchase an already mated female scorpion from a pet shop. In captivity, an ill-fed or stressed female will often eat her newborn young. Even if they survive birth and the jaws of their mother, young captive scorpions rarely survive to adulthood because of their precise humidity requirement during molting.

It has been postulated by scorpion experts that the sex pheromone of some scorpions is not only used to secure a potential mate but is commonly used to attract dinner. Apparently some larger species of scorpions will duplicate the sex pheromone of different smaller species. Then, when males of the smaller species begin juddering, the larger scorpion quickly finds and consumes the one-course meal (fresh scorpion, yum-yum!).

Scorpions have been found in many fossil records, including marine Silurian deposits, coal deposits from the Carboniferous Period and in amber. The oldest known scorpions lived around 430 million years ago in the Silurian period, on the bottom of shallow tropical seas. These first scorpions had gills instead of the present forms’ book lungs. Currently, 111 fossil species of scorpion are known. Unusually for arachnids, there are more species of Paleozoic scorpion than Mesozoic or Cenozoic ones.

The eurypterids, marine creatures which lived during the Paleozoic era, share several physical traits with scorpions and may be closely related to them. Various species of Eurypterida could grow to be anywhere from 3.9 to 98 inches in length. However, they exhibit anatomical differences marking them off as a group distinct from their Carboniferous and Recent relatives. Despite this, they are commonly referred to as "sea scorpions." Their legs are thought to have been short, thick, tapering and to have ended in a single strong claw; it appears that they were well-adapted for maintaining a secure hold upon rocks or seaweed against the wash of waves, like the legs of shore-crab.

Scorpions are predaceous, nocturnal animals with over 900 species worldwide. There are 70 species in the United States alone and 45 in California. Scorpions are above ground dwellers and cling to the underside of surfaces, cracks, cliffs, bark and stiff leaves of trees. The sting of a scorpion is either localized or systemic in action. There are 6 families of scorpions, with the family Buthidae having the dangerous species. In most areas of the United States and the world, most scorpions’ (e.g. Figure 8) stings are no more painful or deadly than the sting of a honey bee. However there are always the exceptions. Surely a person who is sensitive to certain venoms might be more vulnerable to scorpion stings.

Desert Hairy Scorpions. The giant desert hairy scorpion (Hadrurus arizonensis) is the largest scorpion inhabiting the South-West of North America and one of the 8-9 species of Hadrurus in the US, attaining a length of 6 inches. Its large size allows it to feed readily on other scorpions and a variety of other prey, including lizards and snakes. This species is usually yellow with a dark top and has lobster-like pincers. It gets its common name from the brown hairs that cover its body. These hairs help it to detect vibration in the soil. A similar species is Hadrurus spadix.

It is distributed throughout the Sonoran and Mojave deserts. In Mexico, the species’ range flanks the Sea of Cortez in Sonora and Baja California Norte. In the United States, it is found in the western two thirds of Arizona, the Colorado and Mojave Desert regions of southern California, southern Nevada, and extreme southwestern Utah. Arizona Desert Hairy Scorpions are a warm-desert species, specially adapted to hot and dry conditions. They are usually found in and around washes or low-elevation valleys where they dig elaborate burrows (up to 2.5 m deep) and emerge at night to forage for prey and mates

Desert Hairy Scorpions are not especially venomous, but another Sonoran Desert species, the Arizona Bark Scorpion (Centruroides sculpteratus) can be dangerous to young, elderly, and those with compromised immune systems. Arizona Bark Scorpions are commonly encountered in rocky habitats but sometimes stray to sandy soils and are found alongside the Desert Hairy Scorpions.

It is a burrowing scorpion, but is commonly found under rocks containing moisture. Its diet consists of large insects, spiders, and small vertebrates. This is an aggressive and active scorpion, which, as with all scorpions, is nocturnal. Like all scorpions, the giant desert hairy scorpion gives birth to live young, which remain on the mother’s back for a week or more before leaving.

Although this scorpion is big, its venom is not very potent, and its sting is commonly perceived to be about as painful as a honeybee’s sting, this scorpion has an LD50 value of 168 mg/kg. However, an allergic reaction to its venom can be fatal; symptoms can include: difficulty breathing, excessive swelling, and prolonged pain.

Desert Hairy Scorpion. Image Courtesy of

Emperor Scorpion. Keeping arthropods as pets has become quite popular in the last few years. The emperor scorpion is a large black species that is commonly available in California pet shops. This is the largest species of scorpion in the world with one variety reaching a body length of over 5 inches. The emperor has very large pedipalps but is reluctant to pinch. It is commonly believed that the sting of this species results in little more than a tingling sensation. In most cases this is true. I have been stung by this species on a dozen or more occasions. The emperor is very slow moving and typically cannot insert the stinger deeply as the victim quickly pulls away. However, on one occasion I carelessly inserted my hand into a container containing an emperor, which braced itself on the side of the container and deeply drove the stinger in. The pain was considerably worse than that from a bee sting with accompanying heart palpations.

It is not a good idea to handle any scorpion. Even with the relatively harmless species there is always the chance of an allergic reaction to a sting. If someone insists on handling a pet scorpion the very tip of the stinger can be cut off. This does not hurt the animal and renders it harmless, except for those species that can deliver a hard pinch.

Emperor scorpions. A species commonly sold in pet shops.

Bark Scorpions. A few dangerous Centruroides species (bark scorpions) are found from Arizona to Florida, and Mexico. In Arizona, Centruroides sculpteratus is a dangerous species accounting for 75 human deaths from 1926 to 1965, mostly children and babies, twice as many as all other forms of US venomous animals (except the honey bee) combined, including poisonous snakes. They have long and narrow pincers and tail segments and are yellow to reddish in color with 2 dark stripes down the back. There are 3 color phases of this arthropod. Centruroides scultperatus has neurotoxic venoms that have a marked effect on nerve transmission. C. suffusus, the Durango scorpion, is found in Durango, Mexico. Symptoms of this sting are sharp pain, numbness, drowsiness, itching of the mucous membranes, sneezing, excess saliva production with swallowing, sluggish tongue, muscle contractions, reaction to strong light and hemorrhaging of the stomach and lungs. Death can occur in about 3 hours. A sting site should be iced to prevent spread of the venom and treatment must be sought immediately from a physician. There is an effective antivenin available and if treated death can readily be avoided. In adults, death from the sting of one of these scorpions is unlikely. Stings in small children or babies can have serious consequences that are not only serious but also sometimes fatal.

A species of Centruroides, one of, if not the most, deadly scorpions in the United States. Image courtesy of Whitney Crenshaw, Colorado State-Bugwood.

Recently, this species was found infesting several blocks in Anaheim Hills. California. Apparently a pregnant female was accidentally introduced from a recreational vehicle that had been stored for several months along the Arizona side of the Colorado River. This population was eradicated by Orange County Vector Control.

Stings from Centruroides in the United States result in little more than an average of one death a year in the United States. However, in Mexico hundreds of deaths are recorded each year. These deaths are not due to the lack of adequate medical facilities but primarily due to excessive exposure. Many of the homes in northern Mexico are more open to the environment. One of the biggest problems is the use of thatched roofs, which make excellent hiding and easy access to the interior of the houses. Up to 40 or 50 of the Centruriodes scorpions have been collected from one roof. The primary victims are babies that naturally are more susceptible to the sting (more venom per body weight.). When a baby rolls over on a scorpion in its crib, the parent may not know what is wrong before it is too late.

Fat-tailed Scorpion. This is the common name given to scorpions of the genus Androctonus, which is one of the most dangerous groups of scorpion species in the world. They are found throughout the semi-arid and arid regions of the Middle-East and Africa. They are a moderate sized scorpion, attaining lengths of 10 just under 4 inches. Their name is derived from their distinctly fat metasoma, or tail. Their venom contains powerful neurotoxins and is especially potent. Stings from Androctonus species are known to cause several human deaths each year. Several pharmaceutical companies manufacture an antivenom for treatment of Androctonus stings.

Fat-tailed Scorpion. Image Courtesy of Guy Haimovitc

Androctonus is widespread in North and West Africa, the Middle East and eastwards to the Hindukush region. Countries where Androctonus species live include: Morocco,Algeria, Tunisia, Libya, Egypt, Togo, Israel, India, Lebanon, Turkey, Jordan, Saudi Arabia, Yemen, United Arab Emirates, Kuwait, Iraq, Iran, Afghanistan, and Pakistan.

A rough English translation of the name Androctonus is "man-killer", from the Greek andras (άνδρας), meaning "man" and kteinein (κτείνειν), meaning "to kill". Crassicauda means fat-tailed, from the Latin crassus meaning "thick" or "fat" and cauda, meaning "tail". Androctonus crassicauda is widespread throughout the Middle East and its name means "fat-tailed man-killer". Similarly, the Latin word for South is australis, from which Androctonus australis, "southern man-killer", derives.

Scorpion Venom and Modern Medicine: Scorpion venoms are possibly finding some use in modern medicine. The venom of the dangerous death stalker scorpion acts like a smart bomb that seeks out cancer cells. In laboratory tests scorpion venom, armed with radiation or anticancer drugs, may kill cancer cells one at a time preserving the rest of the healthy tissues. Scientists at University of California, Irvine (UCI) have isolated and synthesized a chemical (name: TRAM) in the arachnid’s venom that eventually could become a drug to treat autoimmune diseases -- disorders in which the immune system attacks itself. It has great potential for the treatment of rheumatoid arthritis, multiple sclerosis and lupus.

In principle, it should also work on about 60 other autoimmune disorders, but that won’t be known without extensive testing. The compound also holds promise for organ transplant patients, whose immune systems must be prevented from rejecting the new body part.

During tests, the UCI researchers found the compound suppresses the immune system’s T-cells, which trigger any fight against invaders. (The T-cells are the same cells the AIDS virus destroys.) Like scorpion venom the synthetic compound blocks a cell membrane channel called IKCa1.

Animal and insect venoms have long been a source of medicine for humans. Scientists are just taking advantage of evolution. There are many creatures that have developed venoms to kill prey and for use for self-defense. For instance, a tree bark, from which we get tamoxifen, is useful as a breast cancer drug; curare, which is derived from frog venom, is the basis for synthetic compounds that are used as muscle relaxants in anesthesia. And a new drug from the sea snail, Conex georaphica, will be used for intractable pain.