Threat Display - in Arachnids

In Arachnids

Both spiders and scorpions are venomous, so their threat displays can be considered generally aposematic. However, some predators such as hedgehogs and spider-hunting wasps (Pompilidae) actively hunt arachnids, overcoming their defences, so when a hedgehog is startled by, for instance, the sounds made by a scorpion, there is reason to describe the display as deimatic.

Spiders make use of a variety of different threat displays. Some such as Argiope and Pholcus make themselves and their webs vibrate rapidly when they are disturbed; this blurs their outline and perhaps makes them look larger, as well as more difficult to locate precisely for an attack. Mygalomorphae spiders such as tarantulas exhibit deimatic behaviour; when threatened, the spider rears back with its front legs and pedipalps spread and fangs bared. Some species, such as the dangerous Indian spider Poecilotheria regalis have bright colouring on the front legs and mouthparts which are shown off in its threat display when it "rears up on its hind legs, and brandishes the fore limbs and palpi in the air".

Scorpions perform deimatic displays; when provoked, they spread their pincers and in some cases raise their abdomens, their tails standing near-erect with the sting ready for immediate use. Some scorpions in addition produce deimatic noises by stridulating with the pedipalps and first legs.