Here’s a fantastic shot of a blister beetle showing off its name sake (Thanks to Paul for the picture!). When handled or otherwise disturbed (such as by a hungry predator) beetles in the family Meloidae secrete hemolymph, the insect equivalent to blood, from their joints. In the above picture you can see the drops of yellow fluid at the beetle’s “knees.” The hemolymph contains a toxin called cantharidin, which can cause skin irritation and blistering in humans and can be fatal to ingest. Basically, they bleed poison.
The fellow above is male, as recognizable by the antennal kinks. These kinks are used by males during courtship to entwine with the female’s antennae (
someone blogged about this recently with excellent pictures, but I can seem to find the post*). Only the male beetles produce cantharidin, but they pass it along to females as an extra benefit to mating. Among blister beetles cantharidin actually functions as a female attractant. Cantharidin extracts from blister beetles are used medically to remove warts and even tattoos. Horses are particularly sensitive to cantharidin, and cantharidin toxicosis, caused by ingestion of alfalfa or hay products contaminated with blister beetles, can cause symptoms varying from “depression to severe shock to death.”
*Edit: Found it! TGIQ wins about a million points for the phrase ‘antennal foreplay.’