This sea slug makes its prey do half the food catching

Kleptopredation
klep-toe-preh-day-shun n.
A food-gathering strategy of eating an organism and the meal it just ate.

A wily sea slug has a way to get two meals in one: It gobbles up smaller predators that have recently gulped in their own prey.

“Kleptopredation” is the term Trevor Willis of the University of Portsmouth in England and his colleagues propose for this kind of food theft by well-timed predation.

Researchers knew that the small Mediterranean nudibranch Cratena peregrina, with a colorful mane of streamers rippling off its body, climbs and preys on pipe cleaner‒skinny, branched colonies of Eudendrium racemosum hydroids, which are distant relatives of corals. The nudibranchs devour the individual hydroid polyps and, new tests show, prefer them well fed.
In experimental buffets with fed or hungry polyps, the nudibranchs ate faster when polyps were fat with just-caught plankton. In this way, at least half of a nudibranch’s diet is plankton. This quirk explains why some biochemical signatures that distinguish predators from prey don’t work out clearly for nudibranchs and hydroids, the researchers report November 1 in Biology Letters.

A weird echo of this meal-stealing strategy shows up in certain jumping spiders. The arachnids don’t have the biology to drink vertebrate blood themselves. Instead, they catch a lot of female mosquitoes that have just tanked up (SN: 10/15/05, p. 246).