The Osmeterium is a defence mechanism that all Swallowtail butterfly caterpillars have. Swallowtails are the big butterflies like Cairns Birdwings, Orchards and Ulysses.
The osmeterium is an organ above the head of the caterpillar in the first body segment. If the caterpillar feels threatened, two bright red or orange horns pop out, as well as a very smelly, bitter fluid.
We know it is bitter because one of our lab staff members licked a Ulysses caterpillar once and spent the next few minutes with a nasty taste on her tongue!
This warning system will teach most predators (and silly lab staff!) to back off.
Osmeterium in some caterpillars resemble a forked tongue, combined with spots that look like eyes – in fact, the caterpillar looks just like a snake.
This is one of our Cairns Birdwing caterpillars showing its Osmeterium. Handsome, isn’t it?