Steven J. Prchal

Scorpions have changed little in the 350 to 400 million years since they first climbed from the primal seas and took their place among earth’s first terrestrial arthropods.

The long, segmented body of the scorpion is divided into two obvious sections: the elliptically shaped body and the trade-mark “tail.”The body of the scorpion is divided into two parts, the cephalothorax and the mesosoma or preabdomen. The cephalothorax contains all of the sensory, locomotion, and feeding appendages. Two pairs of chelicerae, positioned on either side of the mouth, allow the scorpion to rip and tear its prey while feeding. Combining the sensitivity of antennae with the grasping ability of a hand, the pedipalps (pincers) are used for sensing as well as holding prey while envenomating or eating. Male and female scorpions also use the pedipalps to clasp their mates during elaborate mating dances. Like all arachnids, scorpions have four pairs of jointed legs. Sensory hairs on the legs can detect the vibrations of prey up to 1 foot (30 cm) away. Dorsally the cephalothorax is covered by the carapace. A pair of median eyes atop the carapace, as well as several lateral eyes arranged into two groups along its front edge, give the animal its limited vision.

The mesosoma contains the paired genital openings, the spiracle slits that open into the tracheal system allowing the scorpion to breath, and the pectines, a pair of comb-like appendages on the ventral surface that sweep the ground possibly as contact pheromone detectors. The pectines may also help the male find a suitable place to deposit his spermatophore during mating.

Class: Arachnida

Order: Scorpiones

Families: Buthidae, Diplocentridae, Iuridae, Superstitionidae, Vaejovidae

Arizona Upland genera: Hadrurus, Vaejovis, Centruruoides, Superstitionia

Spanish name: alacran

The metasoma (tail) of the scorpion is actually an extension of the abdomen. It consists of five segments, each one longer than the last; at the tip is the telson (stinger), which is not considered a true segment.

Bark scorpion

A scorpion uses its venomous sting primarily to subdue insect prey. It also uses the sting defensively, readily stinging a predator or the mistakenly placed bare foot.

Three species of scorpions are commonly found in the Arizona Upland subdivision of the Sonoran Desert. They are the bark scorpion, Centruroides exilicauda, the striped tail or devil’s scorpion, Vaejovis spinigerus, and the giant or desert hairy scorpion, Hadrurus arizonensis.

Although more than 30 species of scorpions are found in Arizona, only the sting of the bark scorpion is considered to be truly life threatening. Its slender shape, and its long, delicate pincers and tail distinguish it from other more stoutly-built species in the state. Of the three most commonly seen species, the bark scorpion is the only one that prefers to climb, and it may be found many feet above the ground on trees and rock faces. Because bark scorpions display negative geotaxis, that is they orient themselves upside down, people are often stung by them as they pick up an object and press against a scorpion clinging to the underside. Defensive stinging is usually a series of quick jabs, after which the scorpion makes a hasty retreat.

Its preference for climbing and natural attraction to cool moist areas and air flows makes C. exilicauda a frequent urban guest. Inside the house, scorpions may be seen trapped in sinks and bathtubs or hiding in dark areas of the closet or storage room. They may also be found climbing walls or clinging to the ceiling. Outside, Centruroides exilicauda frequently lives in lumber or brick piles. The only species tolerant of others, bark scorpions may be found in large aggregations, especially during their winter hibernation. Bark scorpions live in Baja California del Norte, northern Sonora, southeastern California, extreme southeastern Utah, Arizona and southwestern New Mexico.

Stripe tailed scorpion

The stripe tailed scorpion is Arizona’s most common species of scorpion. This species occurs in a variety of habitats from near sea level to 7000 feet (2100 m) in Texas, New Mexico, Arizona, southern California, Sonora, and northeastern Baja California del Norte. These sturdy, medium-sized scorpions are usually under rocks during the day. Like all scorpions, they are nocturnal and venture from their shelters at night to forage for prey. A stout tail with darkly-marked ridges running lengthwise along the underside and a total body length of about 2 inches (5 cm) identify this most common desert ground dweller.

The giant hairy scorpion is one of the least common of Arizona’s desert scorpions and the largest scorpion in the United States (up to 6 inches [15 cm] long). It can be found at lower elevations in southern Utah, southern Nevada, southeastern California, Arizona, and northern Sonora. Its large size allows it to feed readily on other scorpions and a variety of other prey, including lizards. Burrowing deep in the desert soil, H. arizonensis often follows the moisture line. As summer progresses and the moisture level in the soil recedes, the scorpion follows it, creating burrows as deep as 8 feet (2.5 m) below the surface. A giant hairy scorpion frequently assumes a strong defensive posture when threatened, curling its body and tail high overhead and spreading its pincers. The stinging action is swift and well directed, but the sting is mild, causing only local pain and swelling.

Ecology

Giant hairy scorpion

While scorpions are well equipped for survival, they are not without their natural enemies. Scorpions not only feed upon each other but are prey to other animals as well. Elf Owls have been photographed bringing scorpions with their telsons removed to their young. Lizards and small fossorial snakes in the genera Chilomeniscus, Chionactis, and Sonora also find them suitable food. Grasshopper mice and desert shrews are known to feed on scorpions, as are pallid bats.

Scorpions give birth to live young through the summer months, frequently having retained sperm from mating the previous year before going into hibernation. Scorpions are not fully developed when they are born, and will continue to develop until the first molt of their exoskeleton in 7 to 21 days, depending on the species. As the babies are born, they quickly crawl up their mother’s pincers and legs to take a position on her back, where they will safely ride until they molt. Should they fall off, they can become prey—not only for a variety of arthropod predators, but also even for their mother.

One of the most fascinating things about scorpions is that they fluoresce under ultraviolet light, probably due to the complex substance in the epidermis that makes it impermeable. To truly appreciate the lives of scorpions, take a black light out to the desert on a warm, moonless night. You’ll be amazed at how common scorpions are in the undisturbed Arizona Upland habitat. You can also use this technique to observe these ancient nocturnal arachnids as they detect and capture prey, court and mate, and dig burrows. These behaviors are never seen when scorpions are encountered by turning over rocks and other materials where they spend the daylight hours. Not only can you find scorpions in nature using ultraviolet light, you can use this same technique to look for scorpions in and around your home.

Renée Lizotte

Spiders and spiderlike animals belong to the class Arachnida. Arachnids differ from most other arthropods in having no antennae. All adult arachnids have four pairs of legs and have no wings. They usually lack mandibles, having instead fang-like mouthparts to pierce and break up prey.

Spiders are soft-bodied arachnids with two body parts: the fused head and thorax, called the cephalothorax, and the abdomen, also known as the opisthosoma. Spiders have four pairs of walking legs and a fifth pair of appendages, located just behind their mouthparts, known as pedipalps. Pedipalps are not used for locomotion but often assist in touching and maneuvering prey. Each male pedipalp is equipped with a special structure that is used to transfer sperm to the female. This apparatus makes the male palp enlarged; it is often described as resembling a boxing glove. The mouthparts, called chelicerae, each end with a fang. The fang is connected to the venom gland, which enables the spider to inject venom into its prey.

Venom

All but a few species of spiders are venomous. (A notable non-venomous example in the Southwest is the feather-legged spider.) While most spiders are venomous, few are dangerous to humans. In Arizona, only the widows (black widow) and the brown spiders (brown recluse types) have venom dangerous to people. Other species may bite and cause some local swelling, but unless one is allergic to the venom, no medical attention is necessary.

Venom in spiders has two functions: prey capture and defense. In its most common use, spiders bite their prey and inject venom, which immobilizes the prey and starts the process of digestion. Spiders have no teeth and rely on the venom to liquefy their prey in order that their stomachs, known as sucking stomachs, can draw in the meal. Some of the larger spiders, such as tarantulas and wolf spiders, have projections on the inside of their chelicerae that help break the prey into smaller pieces to aid digestion. These hunting spiders typically leave a small pellet of crushed exoskeleton after eating, whereas the smaller web-building spiders leave an empty shell of the former prey, neatly cocooned in silk.

The second function of venom is for defense. A spider that is threatened by restraint or by touching may bite. The spider controls the amount of venom injected and may inject none at all. A black widow could bite when its hiding place under a rock or a log is exposed. People are sometimes bitten by brown spiders that have taken up residence in clothes that have been left piled on the floor or in a tent overnight.

Senses

Spiders typically have eight eyes, although some species have a reduced number. The brown spiders have only six, while some cave-dwelling spiders have no eyes at all. Although most spiders have eyes, only one group, the jumping spiders, rely on their eyes to hunt. Other spiders use their eyes to orient when wandering or to detect motion in the initial stages of prey capture. Spiders are equipped with special hairs, mostly on their legs, through which they feel, taste and hear. Even at a distance, spiders can “feel” where their prey is by the displacement of air around these hairs.

Silk

The diverse use of silk is the most characteristic feature of spider, which have at least four, but more typically six, spinnerets (appendages that spin silk). A spider may have up to six types of silk gland, each producing a different kind of silk. It is actually a complex strand of proteins that is produced as a liquid, and solidifies under tension. Silk is used to build webs, catch food, line burrows, protect eggs, detect prey (as trip lines), and even to aid in dispersal. This dispersal phenomenon is known as ballooning. Spiderlings (baby spiders) climb to the top of an object or plant and let out silk. The spiderlings are so light that, as the air currents take up the silk, the spider is transported, sometimes miles away. Some of the larger spiders, such as tarantulas, are too heavy to balloon, but most smaller species have this ability.

Ecology and Life History

Spiders are predators. They survive by eating other animals such as insects, crustaceans, or even other spiders. Thus when spiders get together it can be potentially life-threatening. But spiders have developed special ways of communicating with each other to avoid cannibalism. Male spiders warn female spiders of their presence by plucking their webs, exchanging chemical signals, tapping the surfaces females are resting on, or producing audible drumming or scrapings. Each species has a specific code, and its use prevents most cannibalism.

Among insects, the primary predators on spiders are spider wasps in the family Pompilidae. Different species of wasps have different strategies, but the result is the same: the wasp lays an egg on the immobilized spider, and when the wasp larva hatches, it eats the spider. Most wasp species do not hunt particular spider species, though they may prefer one over another. Interestingly, the spiders rarely defend themselves when attacked by wasps.

Male spiders, which reach maturity at an earlier age than females, must search for a mate. With the exception of tarantulas, spiders typically mate one time during their lives. The average spider lives for approximately one year, but some of the larger wolf spiders live about two years; and tarantulas may live up to twenty years. The male web-building spider sometimes guards the web of an immature female from other males, mating with her immediately after the molt in which she becomes an adult. Males of other species must go through an elaborate courtship of song and dance before the females will accept them. Once the female has mated, she can store sperm for several months up to a year. She may produce 2 to 3 egg cases during that time. Depending on the species, a few to a few hundred eggs may be laid per egg case, but usually each subsequent egg case is smaller with fewer viable spiderlings.

Adaptation to Desert Life

Spiders are fairly tolerant of environmental extremes. They can adjust their body temperatures to be higher or lower than the ambient temperature by, for example, sunning to warm up, or by escaping into the shade or a burrow to cool down. High body temperatures threaten the loss of water as vapor through transpiration; a loss amounting to over 20 percent of the spider’s body weight is lethal. Spiders can drink, even from moist soil. Many spiders are nocturnal, which means that they are active only during the cooler, more humid parts of the day. Spiders can survive cold winter temperatures by moving to relatively warm micro- climates such as burrows or leaf litter; they curl up to reduce exposure, become rigid and reduce their meta-bolic rate.

Arizona blond tarantula Aphonopelma chalcodes

Family: Theraphosidae
Other common names: desert tarantula, western tarantula
Spanish name: tarántula

Description

This 3 to 4 inch (70 to 100 mm) large bodied, burrowing spider is commonly seen during the summer rainy season in southwestern deserts. The female is usually a uniform tan color. The male has black legs, a copper-colored cephalothorax and a reddish abdomen. Their burrows can be as large as 1 to 2 inches (25 to 50 mm) in diameter, with some strands of silk across the opening.

Distribution and Habitat

The Arizona blond tarantula is typically found in saguaro-dominated plant communities. There are many similar species throughout the desert southwest, but they are difficult to differentiate.

Ecology

Tarantulas are nocturnal predators that never venture far from their burrows unless it is mating season. In winter they plug their burrows with soil, rocks, and silk and survive in a relatively inactive state. During this time the animals live off stored fat reserves.

Tarantulas have an interesting defensive capability in addition to venom. Some of the hairs on the top of the abdomen are specialized for defense. These urticating hairs, as they are called, are tipped with backward pointing barbs. If a tarantula is threatened in any way, it brushes these hairs into the face, paw or other body part of its attacker. Once these hairs are embedded, they are irritating and very difficult to remove because of the barbs.

Life History

Arizona blond tarantula

Male tarantulas mature when they are 10 to 12 years of age, at which time they leave their burrows in search of females. Upon finding the burrow of a mature female—she’s usually at least 10 years old—the male will announce himself by stroking the silk at the top of the burrow and tapping particular sequences that the female responds to. During mating, the male must reach under the female to insert his pedipalp into her gonopore to deposit sperm. He is particularly vulnerable to predation by the female when mating. The male’s first pair of legs has a “spur”located behind the knee which he uses to hold the female above him during copulation. After copulation the male makes a hasty retreat. The female lays her eggs in a burrow, sometimes staying with them. The young remain in the burrow until they disperse.

Each time a female tarantula molts, typically once a year, she also molts the lining of her epigynum (the female reproductive structure) where the sperm are stored, so she must mate again before she can produce fertile eggs. The many tarantulas seen on the roads in Arizona during the summer rains (July, August, September) are usually males searching for mates. The male tarantula does not survive long after his summer mating. Sometimes the female makes a meal of the male, or another predator kills him. Sometimes he dies of exposure to heat and cold. Even in captivity, out of harm’s way, males only survive a few months after mating.

wolf spider Hogna carolinensis

Family: Lycosidae
Spanish names: mordelena, carga hijas, buena madre

Description

Wolf spiders are large, with a 1 inch (25 mm) body length; like tarantulas, they live in burrows. Wolf spider burrows can be differentiated from tarantula burrows by the turret of silk and twigs that extends vertically from the wolf spider’s hole. The wolf spider can be from gray to dark brown with distinctive peach or orange coloration on the front of the chelicerae.

Distribution and Habitat

This particular species of wolf spider is found throughout the United States in habitats ranging from desertscrub to woodlands.

Ecology

Wolf spider

These spiders are most often found in Arizona Upland habitat, where their burrows are quite conspicuous. They are typically active from March through October, when their green eye shine can be easily seen as they cross roads at night. The eye shine is caused by a tapetum in the eye which reflects light rays back through the eye retina and probably enhances the spider’s night vision. Wolf spiders are primarily nocturnal predators and are rarely seen during the day.

Life History

Wolf spiders are expert and vigorous hunters. Adult males can be found wandering throughout the summer rainy season, presumably searching for mates. The male must give the female appropriate signals when he finds her, to avoid being perceived as a threat. He does this by tapping his legs in a particular fashion. He also drums with his palps, and in a procedure called stridulation, he produces sounds by scraping the palp against itself. After the female lays eggs, she carries the egg case with her wherever she goes, attached to her spinnerets. Sometimes she suns the egg case, sticking her rump, with egg case attached, outside the burrow entrance. The spiderlings hatch after about a month and climb onto the mother’s back, holding onto specialized hairs. After another month, they disperse, sometimes by ballooning. A female wolf spider may live up to 2 years.

labyrinth spider Metepeira arizonica

Family: Araneidae

Description

The web of this spider is more easily recognizable than its body. The labyrinth spider most commonly constructs its web between the pads of prickly pear cactus. It builds an orb web, behind which is a tangled, disordered web made with some debris woven into the silk. Below the debris is a silken retreat in which the spider hides. The spider is small, about ¼-inch (12 mm) long, with a bulbous abdomen and thin delicate legs. The carapace is brown or grey; the abdomen is dark with a distinct white pattern.

Distribution

This spider is found in Arizona and California.

Ecology

Like many other spiders, the labyrinth spider is a predator that uses the orb portion of its web to ensnare prey. It is a passive hunter that lets the web do the work. Small insects that visit the prickly pear cactus to drink nectar or eat the fruits sometimes inadvertently fly into the labyrinth spider’s web.

Life History

The labyrinth spider is active, with its webs visible in prickly pears, from March through October. During the rainy season the female mates and lays eggs. She builds an egg case around the eggs and hangs it in her web near her retreat where it is camouflaged by other debris in her web. Once the young emerge they are self-sufficient; they disperse by ballooning.

funnel-web spider Calilena arizonica, Hololena hola, Novalena lutzi

Family: Agelenidae
Spanish name: zacatera

Description

The funnel-web spider is similar in appearance to the wolf spider, but it is smaller and more delicate, with a body length of about ¼ inch (12 mm). It builds a sheet-like web with a distinct funnel shape leading to a retreat. Because these webs are often built in grasses, a common name for these arachnids is “grass spider.”

Distribution and Habitat

Funnel-web spiders live world-wide; these three species are common in southern Arizona. They build webs in grass or leaf litter, on stones, or in the corners of buildings.

Ecology

These spiders use their webs to catch prey. The sheet of the web acts as a catch basin for insects that blunder onto it, becoming stuck in the sticky silk. The spider, sensing the vibrations in the web, goes out to retrieve its meal. If the prey item is small enough, the spider will cut it out of the web and bring it down into its retreat to feed on.

Life History

Funnel-web spiders are active from March through October. A male spider must communicate to the female via stridulations and web stroking. Once the female accepts him onto her web, mating takes place. The female lays 100 to 200 eggs in an egg case. She weaves the egg case into her web, near or within her funnel retreat. After about a month the eggs hatch and the young disperse, often by ballooning.

giant crab spider Olios giganteus

Family: Hetropodidae (Sparassidae)
Other common names: huntsman
Spanish name: cazadora del desierto

Description

One of the largest in this area, this spider has a leg span of 2 to 2¼ inches (50 to 64 mm). It is medium to light brown. It often extends its legs at right angles to its body. It can move sideways rapidly, hence the name “crab” spider. Despite its large size, it is capable of climbing fairly smooth vertical surfaces and is often seen high on walls or even ceilings of dwellings. This is one easy way to distinguish it from the wolf spider, a non-climber.

Distribution and Habitat

Giant crab spider

Though it belongs to a group of spiders which is mostly tropical, the giant crab spider is found throughout Arizona and Sonora, in a variety of habitats, such as in dead saguaros, under rocks, and in dwellings.

Ecology

This is a hunting spider that wanders in search of insect prey, then relies on speed to catch it. During the day it hides, its flattened body perfectly designed for fitting into narrow cracks or fissures. At night it comes out to hunt. Reportedly, its bite is painful, though it is not dangerous to humans. These spiders generally settle into one place only at egg-laying time. Females produce large egg bags that they hide in and guard.

green lynx spider Peucetia viridans

Family: Oxyopidae
Spanish name: araña verde

Description

Green lynx spider

This is a very bright green spider, about ¾ inch (19 mm) in length, with long, spiny legs and an oblong to oval abdomen.

Distribution and Habitat

This spider, which is a member of a spider family that is mostly tropical, is found in southern United States from coast to coast, and also in Mexico and Central America. It often lives in clumps of prickly pear cactus.

Ecology

Lynx spiders are hunters specialized for living on plants. This species does not use a web to capture its prey. In our region, it often lies in wait for insects in the blooms or on the pads of prickly pear, for which its bright green color offers ideal camouflage. It pounces on its prey in a cat-like manner, which is the reason for the name “lynx.” It is active during the day.

Life History

The inseminated female lays her eggs in a sac that she hangs in a web. She hangs above it, hugging it with her legs. The female guards her eggs and the newly hatched young until their first molt.

brown spider
Loxosceles spp.

Family: Sicariidae (Loxoscelidae)
Other common names: violin spider, Arizona brown spider, fiddle spider, necrotizing spider, brown recluse Spanish name: uvari

Description

This is a small, inconspicuous brown spider with slightly darker brown markings on the cephalothorax. These markings vaguely resemble the shape of a violin, hence the common names “violin”or “fiddle” spider. The species native to this area are closely related to the infamous brown recluse of the midwestern United States, but the markings are less obvious.

Distribution and Habitat

Brown spider

These spiders occur in the southern United States through Mexico and Central America. Not all species live in the desert, but several species of Loxosceles are found in Arizona. These secretive spiders are found in debris in the desert or around dwellings in outlying areas.

Ecology

A trapping spider, the brown spider catches insects and other invertebrates in sticky, irregular webs spun beneath rocks and debris. The bite of this spider is potentially dangerous to humans: reportedly some have suffered amputation and even death as the result of bites. Although sometimes the bite causes little harm, the most common reaction is a spreading sore at the site of the bite, which, if untreated, may result in permanent tissue damage. Those who suspect a brown spider bite should see a physician.

Life History

The inseminated female lays eggs in cases. Once hatched, the young may live 2 to 3 years.

Family: Theridiidae
Other common names: western black widow
Spanish name: viuda negra

Description

The female of this sexually dimorphic species is usually ¼ to ¾ inch (12 to 19 mm) in body length, shiny black or very dark brown, with a large rounded or oval abdomen which is characterized by a bright red-orange hourglass shape on the underside. The male is less than half the size of the female, medium brown with cream-colored markings on legs and abdomen. The young of both sexes resemble the male.

Distribution and Habitat

Different species of Latrodectus are found throughout most of North America, more commonly in warmer climates. Black widows are common around man-made structures such as garages, lawn furniture, and woodpiles. They also live in a variety of natural habitats.

Ecology

Black widow spider

The black widow preys mainly upon insects that it traps in the web. The web is irregular and strong to the touch in comparison to other webs. Some species of spider wasps prey upon black widows. Black widows are shy, sedentary, and largely nocturnal. They are not aggressive, but will bite in self-defense.

Life History

The female mates only once in her lifetime, retaining sperm for future egg-laying. The smaller male is sometimes eaten by the female following mating, hence the name “widow.” This characteristic, however, is not limited to black widows, but can occur after mating in many arachnids, most of which are highly predatory. The female lays approximately 300 eggs at one time and encases them in a round, cream-colored egg sac made of her silk. One spider produces several sacs within its one- to two-year lifespan, but only one sac at a time. The spiderlings disperse by ballooning.

The black widow is one of two species within our region that is potentially dangerous to humans (the brown spider is the other). The bite can kill a human, but this is rare. More often, the bite is painful and causes serious reactions, including nausea, dizziness and abdominal cramps.

trapdoor spider Ummidia spp.

Family: Ctenizidae
Spanish name: araña terafosa

Description

Trapdoor spiders are close relatives of tarantulas, and their general appearance is similar, but they can be distinguished by their small size, less hairy abdomens, and legs that shine almost as if polished.

Distribution and Habitat

These spiders range from Virginia south to Florida and west to California. Trapdoor spider tubes are usually found in the sides of banks in disturbed areas.

Ecology

Trapdoor spiders prey on large terrestrial arthropods, and even occasionally on small lizards. They themselves are preyed on extensively in some areas by parasitic wasps of the family Pompilidae.

Perhaps the most interesting aspect of these spiders is their architecture. They build tube-like tunnels in the sides of banks in disturbed areas, along natural insect walkways. The tunnel is capped with an ingenious trapdoor. Trapdoor spiders are well-adapted for the strenuous activity of tunnel-building. Their chelicerae are equipped with digging rakes (rastella) that are used to loosen earth during the digging process, and then to roll it into a ball which is thrown from the developing burrow with strong, spined hind legs. Once the initial tunnel has been constructed, it is reinforced with a coating of a mixture of earth and saliva. Next a layer of silk is added, this being spun in one piece. The last step, the addition of the door, is the part of the process that differs from species to species. Two types of doors may be constructed. The most well-known is the “cork”-type door, which is very thick and beveled to fit the opening exactly. The other is the “wafer”-type door, which is a simply-constructed sheet of silk and dirt. The species also differ as to whether the tunnels are simple, or branching, with multiple doors. In all cases, however, the doors are equipped with silk hinges for easy opening and closing.

Trapdoor spider capturing a cricket

The tunnel is used by the trapdoor spider as shelter from the elements and predators, as a nursery, and as a trapping device. The top of the door is usually camouflaged with bits of debris, such as twigs and rock, making its discovery very difficult. This results in fooling prey as well as predators, thereby making it a very effective shelter and trap. When the spider is using the trap to capture prey, its chelicerae hold the lid shut on the end of the door farthest from the hinge. It awaits the vibrations of passing prey conducted by the silk, quickly throws open the door, grabs the prey and returns with it down the tube. Although the lid stays shut easily on its own, attacks by predators can be discouraged by the spider holding the lid closed with its chelicerae, and, at the same time, bracing its legs against the wall of the tunnel. The only predators that are not dissuaded by this seem to be parasitic wasps, which simply chew right through the door.

The tunnel is also used by the female as a nursery. She lays her eggs in the tube and immediately covers them in a sac which is attached to the tunnel wall. She remains with them until hatching and beyond, allowing them to remain unharmed in the burrow until they are as much as eight months old.

Tailless whipscorpion

Renée Lizotte

Tailless whipscorpions look at first glance like spiders. The first appendages (pedipalps) are modified for grasping prey, with hook-like projections. The first true pair of legs is modified to serve as “feelers,” and are long, delicate, and whip-like, with many fine hairs.

Distribution

Amblypygids are found in tropical regions throughout the world. In Arizona, these animals live in abandoned rodent burrows and along dry river washes in the Arizona Upland foothills.

Ecology

Tailless whipscorpions are reclusive predators of insects. They hunt nocturnally, using their long, delicate first pair of legs to find their food. The spined pedipalps impale and crush the prey and then transfer it to the chelicerae (jaws). Tailless whip- scorpions can only pinch their prey; they lack venom glands.

Life History

After stroking females with the whip-like front legs, males deposit a spermatophore on the ground. The females then pick up the sperm masses with their gonopores. After females lay the eggs, they will carry them until they hatch, and then carry the young for 4 to 6 days.

sun spiders

Sun spider

Sun spiders are 1 to 3 inches (25 to 75 mm) long and are yellow or tan in color. They have eight walking legs, long club-like pedipalps and large, muscular chelicerae. The tips of the chelicerae are equipped with pairs of pincers that are quite formidable. When moving, sunspiders often hold their pedipalps in the air.

Distribution

Sun spiders are found throughout the world in mostly tropical and subtropical areas. They are also at home in the hottest, driest deserts of the world.

Ecology

Sun spiders are good predators, able to run down their prey and catch it with great speed. Sun spiders feed upon insects and arachnids, and even small lizards. They are also good diggers and probably spend most of their time underground. They are most active in the desert southwest during the warm months of May and June, and they remain active throughout the rainy season during July, August, and September.

Life History

The mating process begins with a male encountering a receptive female. Some “dancing” and stroking ensues, with the male finally flipping the female onto her back, and with his chelicerae, inserting into her gonopore a sperm droplet. The female stores the sperm for later fertilization, after which she digs a burrow and deposits about 100 eggs. The juveniles are completely independent upon hatching.

Giant desert centipede

Renée Lizotte

Centipedes are arthropods that have elongated bodies with one pair of legs per segment. They range in size from less than an inch to several inches. The giant desert centipede is usually 6 to 8 inches (15 to 20 cm) long, while the common desert centipede is 4 to 5 inches (10 to 13 cm) long. The larger giant desert centipede is orange with a black head and tail. This warning coloration advertises the centipede as dangerous. The smaller, brown and tan, common desert centipede is less so. While painful, neither bite is especially dangerous to humans.

Distribution

Centipedes are found world-wide, in temperate and, more abundantly, in tropical areas. These 2 desert species are found throughout the southern United States and into Mexico.

Ecology

Centipedes use structures called gnathosomes or gnathopods to inject venom into their prey. These are paired pincer-like appendages in front of the legs. The “bite” is actually a pinch. Centipedes are fast-moving predators that feed on any small creatures they can catch—mostly insects, but occasionally other arthropods, lizards, and even small rodents. Centipedes in the desert are strictly nocturnal and spend their days underground or concealed from the sun. They lack the waxy layer in their cuticle that other arthropods have, and are therefore more prone to desiccation than are other terrestrial arthropods.

Life History

Centipede mothers care for their eggs, coiling around them and grooming them. This grooming is thought to protect against mold and bacteria. Once the young hatch, the mother tends them as she did the eggs, until they disperse a few days later.

millipedes

Desert millipede

Millipedes have long, cylindrical bodies with 2 pairs of legs on each segment. New segments and pairs of legs are added each time the millipede sheds. Since it continues to grow and shed throughout its lifetime, it’s impossible to say how many legs a millipede has without counting. The common millipede in southern Arizona is a dark reddish brown, but millipedes in other areas may be tan to golden brown. Most desert millipedes are 4 to 5 inches (10 to 13 cm) long.

Distribution

Millipedes are found world-wide except in polar regions, but are more abundant in tropical climates.

Ecology

Millipedes are detritivores, foraging for decaying organic material (in the desert, generally in sandy washes). They are nocturnal and prefer humid environments, often appearing on roads after soaking summer thunderstorms. They are good burrowers and spend most of their time underground. If disturbed, the millipede rolls into a coil. If further threatened, it exudes foul-tasting chemicals from openings along the sides of its body. These noxious substances are the millipede’s only defense, since it doesn’t bite.

Life History

Millipedes are egg layers that do not care for their eggs or young. The eggs are laid underground or in some other concealed area. Millipedes can live 10 years or more.