Amblypygids
by Virginia Kirby
Taken from Backyard BugWatching#1 Fall Issue 1986

Amblypygids, which include tail-less whip scorpions and whip spiders, are non-venomous, non-silk-spinning arachnids. Taxonomically they belong (along with true whip scorpions) between scorpions and spiders, having a closer affinity to the latter. They differ from the more elongate uropygids in having a rounded anterior and an elongated oval abdomen lacking a telson (tail) and poison glands, and in having the cephalothorax joined to the abdomen by a slender pedicel.

Amblypygids are common nocturnal predators of insects, including: cockroaches, crickets, grasshoppers, beetles, butterflies and wood lice, and also arachnids, and are harmless to people. They can be found in dark moist sites among rocks, under wood debris and logs, as well as in human dwellings. They are not known to burrow.

The animals can move very rapidly, usually sideways like crab spiders, walking on the six posterior legs while using the first pair of legs as antennae to explore the surface being covered. When stationary, these first legs or whips may be slowly rotated, one forward, the other backward to investigate a large area around the body. The extreme tips of the first legs touch the surface, tapping with great delicacy. Amblypygids can climb vertical surfaces in caves. Members of the family Charontidae are also able to climb a vertical sheet of polished glass or walk across the undersurface of a horizontal one.

When stalking prey amblypygids move forward. They touch the prey with the tips of the first legs, then snatch it with one or both pedipalps. The importance of vision in hunting is uncertain. The prey, impaled on the pedipapal spines, is severed as the chelicerae move back-and-forth and up-and-down, masticating the food before ingestion. Liquification of food before ingestion has not been documented, but seems likely, judging from the narrow foregut. After feeding, amblypygids usually fast for several days.

The whips are useful for finding water. An amblypygid drinks by either channeling drops of water to the chelicerae with the pedipalps or inserting the chelicerae directly in the water. Tail-less whip scorpions clean their appendages by running them through their chelicerae, the pedipalps being used to guide the appendages to the mouth. The pedipalpi have brushes on their ends for cleaning each other, which in turn are cleaned by the chelicerae.

When disturbed, amblypygids scurry to cover. Lacking spray glands like the whip scorpions (vinegaroons), they defend themselves with their pedipalps. If two individuals of the same species meet, they touch each other with their whips and the smaller one then moves off sideways. If evenly matched, they tap each other's sides with their whips or, in rare cases, fight with their pedipalpi where one may get injured.

Courtship takes place at night and can be observed by either using a dim light or one covered with a red lens or red cellophane. In three species, Admetus barbadensis, Damon variegatus, and Sarax sarawakensis, the male and female touch each other only with their whips; they do not hold on to each other. For several hours the male strokes and taps the female with his first legs while walking back and forth. Then he stands facing the female, turns 180 degrees, touches the ground several times with his abdomen and then implants a spermatophore (that lacks sperm) in the ground. He then turns to face the female. In Admentus and Damon the male then deposits two masses of sperm side by side on the spermatophore stalk. The male then slowly walks off and is followed by the female, who picks up the sperm masses with her gonopore as she passes over the spermatophore after which the male resumes with tapping the female. The female leaves and the male then eats the spermatophore stalk.

Like whip scorpions (Uropygida), female amblypygids carry their eggs in tough mucus sacs located on the concave ventral abdominal surface. The young molt as they leave the sac to climb on their mother's abdomen where they'll stay for four to six days. If one falls off, the mother may eat it. The second molt takes place on the mother's abdomen after which the young immediately leave their mother. They feed within two days after leaving her.

Young amblypygids molt five to eight times in the first year. When mature, amblypygids molt once or twice a year, continuing to grow throughout life. They live for many years, having two or three broods per year.

0ur local amblypygid, Paraphrynus mexicanus is active during the warmer months of the year. In the Tucson area they are most commonly found in the foothills of the Catalina and Rincon Mountains and in the mesquite bosque on Tanque Verde Road.

Amblypygids resemble spiders in many characteristics (e.g., possessing spider-like chelicerae, having similar internal organ structure and being flattened dorsoventrally), but differ in having long whip-like first legs, strong, armored pedipalpi and in lacking spinnerets. The pedipalpi are the main distinguishing characteristic of the order. They are large, stout, 6-segmented raptatory appendages armed with large spines and ending in a moveable hook. Also characteristic are the elongate antenniform or whip like first legs, which are many-segmented and serve not for walking but as tactile organs.

The prosome, or cephalothorax, is covered by an unsegmented dorsal plate, the carapace, on the anterior surface of which are one pair of median eyes and three pairs of lateral eyes. Whip spiders range in body length from 5-45mm, the span of the first legs reaching 50cm in some species. Secondary sex characteristics in the order are negligible in most species making differentiation between the sexes difficult. For example the femur of the male of the East Asian species Charon greyi is longer in the pedipalp than in the following legs while the reverse is true in the female.

About 70 species are known in the order which is composed of three families: Charontidae, Tarantulidae (Phrynidae being an old name for this family), and Phtynichidae. The three families can be distinguished as following: Charontidae have pulvilli (pads) on the tarsi of the 2nd, 3rd, and 4th legs; Tarantulidae lack these pulvilli and have pedipalpi which form a basket for catching prey and; Phrynichidae, which also lack pulvilli and have an unsegmented tibia on the 4th leg and pincers at the end of the pedipalpi. Paraphrynus, a genus with species in Arizona, belongs to the Tarantulidae; it in turn can be distinguished from other genera in its family by the spine pattern on its pedipalps and the surface structure of the anterior edge of its carapace.

The distribution of the order is limited to some degree by its need for moisture; it is therefore found only in the more humid regions of the tropics and subtropics. It is found from the islands of Rhodes and Kos in the Agean Sea to sub-Saharan Africa, from India and Southeastern Asia to New Guinea and from the southern United States down to Brazil and the West Indies. It is absent in Madagascar and Australia. Paraphrynus occur in Southern California, Arizona, and Florida south into the West Indies and Central America, the southernmost record being in Panama.