Whip spiders walk on six legs and feel their way with two absurdly long whips
Amblypygids look like nightmares, flat-bodied arachnids with spiny grabbing arms and front legs stretched into feelers up to 60 centimetres long. Yet they have no venom and no silk, rarely bite, and see poorly. Counting those whips, the biggest species are the largest arachnids on Earth by legspan.
Also called whip spiders or tailless whipscorpions, the roughly 280 described species live in warm, humid tropical and subtropical places, hiding by day in leaf litter, caves or under bark and hunting only at night. The name means blunt tail, because they lack the whip-like tail of true whipscorpions. Their lineage is ancient: fossils such as Weygoldtina date back to the Carboniferous.
Like all arachnids they have eight legs, but only six are for walking. The first pair has become antenna-like sensors, thin, many-jointed and covered in tiny sense organs that smell, touch and read air currents. That matters because vision barely counts. Most species have eight simple eyes, yet they see poorly, and cave dwellers may lose some or all of them; their main use seems to be spotting dark places to hide when suddenly lit.
Prey is caught with the pedipalps, spiny arms that fold in front of the body and snap shut like a praying mantis's forelegs, often forming a catching basket. In some species they grow enormous: Euphrynichus spans almost 40 centimetres across its extended pedipalps, and males usually have longer ones. Walking legspans run from 5 to 29 centimetres, and the bulkiest body belongs to Acanthophrynus, at up to 45 millimetres long.
They have other tricks. A whip spider can shed a leg at a set joint and regrow it over several moults, and a regenerated whip ends up longer than the original. Some species have adhesive pads on their feet that let them climb glass, and a secreted coating makes their bodies super-water-repellent. Their blood is bluish, carrying oxygen on copper-based hemocyanin instead of haemoglobin.
Source: Amblypygi
