Giant Vinegaroon

Mastigoproctus giganteus — the giant vinegaroon — is one of about 120 species in order Thelyphonida (the whip scorpions or vinegaroons), one of the smallest and most ancient surviving arachnid orders. The species is found across the southwestern US (Texas, New Mexico, Arizona) and northern Mexico in arid and semi-arid habitats. Adults are 4-6 cm body length plus a long whip-like terminal tail (the 'flagellum' or 'telson') that is roughly equal in length to the body — total length 8-12 cm. The body is dark brown to black, with massive heavy pedipalps (the front 'pincers') that resemble a scorpion's claws, eight walking legs, and the diagnostic whip-like terminal tail. The species has NO STINGER, NO VENOM, AND CANNOT INJECT TOXINS — but the absence of conventional arachnid weapons is more than compensated by the species' famous ACETIC ACID SPRAY DEFENSE. The vinegaroon has paired glands at the base of the tail that produce and store concentrated ACETIC ACID (the same chemical found in vinegar, but approximately 85% concentration vs. the ~5% in household vinegar — strong enough to be irritating to mucous membranes and to deter most vertebrate predators). When threatened, the vinegaroon raises the tail, aims the gland openings at the source of the threat, and SPRAYS the acid in a fine targeted mist that can reach up to 1 meter from the body. The spray smells strongly of vinegar (the source of the common name) and is irritating but not seriously dangerous to humans — it can cause temporary stinging of skin and mucous membrane irritation if it gets into the eyes. The species is nocturnal, lives in burrows, and hunts small arthropods at night using the heavy pedipalps to seize prey. Vinegaroons are equally dramatic in mating behavior — males perform elaborate ritualized 'tandem dances' with females lasting up to 13 hours, with the male leading the female by the heavy pedipalps to a spermatophore deposit site. The species is the most-photographed vinegaroon in North American macro nature photography because of the dramatic appearance and the unusual chemical defense.