These elusive critters look like something straight out of a horror movie. They are members of the order Amblypygi and within the arachnid family, which includes spiders1. In contrast to the whip scorpions or vinegarroons (Uropygi)—another order of arachnids—these creatures lack the tails that lend them the partial title of “scorpion”. Though they have the same general structure as spiders, possessing eight legs, a segmented body, and beady little eyes, there are some very stark differences that go beyond this superficial resemblance.
Both the Amblypygi and the Uropygi orders of arachnids lack the silk-spinning spinnerets or poison glands characteristic of spiders2,3. Since they lack these common predation strategies, their raptorial pedipalps have been modified for catching and consuming prey. These structures are similar to those seen on a mantis, and have been enlarged, extended, and covered in spines to allow them to impale prey before consumption. Additionally, their front legs have evolved from locomotor appendages to more of a sensory organ. These antenniform limbs have become thin and elongated to extend out in front of the scorpion as a way of detecting prey. These extremities are covered in sensitive hairs called trichobothria and are present in all arachnids to help detect airborne vibrations and currents.
The combination of these adaptations allows these animals to detect and capture prey whilst hunting. Whip scorpions generally forage at night, walking side-ways in a crab-like fashion with their sensory limbs extended out in front of them. The Amblypygids typically feed on arthropods and moths4, but have occasionally been observed to feed on prawns in the rocky outcrops of the Caribbean5. In general, these animals are sit-and-wait hunters, relying on their specialized sensory organs to detect incoming prey. Once a prey item has been identified and is within reach, the whip scorpion will use its spiny pedipalps to capture it and bring it in for the kill. They will then grind up the tasty morsel with chelicerae organs similar to those in spiders, before consuming its liquefied contents2,3.
Interestingly, in a few species of tailless whip scorpions, these specialized front limbs have also been observed to serve a function in reproductive behavior. In an attempt to court females, males will quiver these skinny legs in the presence of females in concordance with rocking body movements. Afterwards, they deposit a spermatophore—a packet of sperm—and will guide females with their pedipalps over the deposit allowing them to acquire the sperm necessary to fertilize their egg sac. These fertilized eggs will develop on the underside of the female’s abdomen until the eggs hatch and molt, upon which they will migrate to her back and remain there until their second molting2,3.
These hideous, yet fascinating creatures are widely distributed across warm and humid regions. Throughout your travels, if you are in search of such a critter, you are likely to find them in dark, protected places, such as in caves or under leaf litter. If you do encounter a whip scorpion one-on-one, just remember that their scary appearance is mostly a façade. Although their “scorpion” title implies they are dangerous, they completely lack venomous glands and hence are relatively harmless. In short, their bark is bigger than their bite.
[By Josie Hubbard]
1Harvey, M. S. (2003). Catalogue of the smaller arachnid orders of the world: Amblypygi, Uropygi, Schizomida, Palpigradi, Ricinulei and Solifugae. CSIRO publishing.
2Brusca, R. C., & Brusca, G. J. Invertebrates. 2003. Sunderland, MA: Sinauer Associates, 2.
3Barnes, R. D. (1987). Invertebrate zoology (No. Ed. 5). WB Saunders company.
4Hebets, E. A. (2002). Relating the unique sensory system of amblypygids to the ecology and behavior of Phrynus parvulus from Costa Rica (Arachnida, Amblypygi). Canadian Journal of Zoology, 80(2), 286-295.
5Ladle, R. J., & Velander, K. (2003). Fishing behavior in a giant whip spider. Journal of Arachnology, 31(1), 154-156.
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