Knock, Knock Who’s there?
It is Drilus.
Drilus, I am going to eat you!
Bad jokes aside, Drilus is serious about eating someone. This someone is a snail.
The larva of Drilus beetles are the nightmare of any snail. There are two species of Drilus in the Netherlands of which the larva crawl up into a snail shell, paralyze the snail with a bite which is likely venomous and eat the snail afterwards. He might even stick around his stolen home for a couple of weeks and just kick back and relax.
We only have 2 species of Drilus in the Netherlands. Greece however, has many different species of Drilus beetles. Greek snails thought that they could outsmart this ferocious beetle larva by gluing themselves to rocks, leaving only their hard calcium carbonate shell exposed. The biology student Els Baalbergen was sceptical about the snail’s tactic in fooling the Drilus larva. So she decided to look into the subject during a master project at the character evolution group at Naturalis Biodiversity Center. The research, which was performed in collaboration with the University of Patras (Greece), showed that her doubts were not unfounded.
She discovered that the Drilus larva, when unable to enter through the front-door, just made a side-entrance by drilling a hole in the shell. When they were done eating the snail and ready to leave, they just make a second hole to exit the shell (see photo below). She furthermore found that specific species of Drilus prefer specific species of snails for their dinner. She suspects that the shape of the snail shell is under strong selection by these beetles. Sometimes as much as half the snail population dies at the hand of the beetle larva in certain areas. So any change in the form or structure of the snail shell that prevents them from being eaten alive will be strongly selected for.