A horseshoe crab: it is only when you see the shell wet from the water, close up, that you know they are real | Helen Sullivan

They have milky blue blood that can detect toxins - and people in lab coats want it

Every day in bright clinical rooms in countries all over the world, horseshoe crabs are strapped into specially designed harnesses and drained of a third of their blood by people in lab coats. Then they are put back into rivers and oceans to swim-scuttle out their days.

Horseshoe crabs are prehistoric and they look it: a fossilised Roomba most of the way through eating a stingray. The horseshoe crab looks mainly like it should not be alive right now.