It's not often that you see a parent leaving their children in the company of an intruder and hoping they'll be OK, albeit a species of potter wasps known as Allodynerus delphinalis does it anyway. Not only that, but the Ensliniella parasitica, a parasitic mite living in the nest of this particular species of wasps, does a pretty good job as well, chasing away or even killing invaders several times bigger than it, such as parasitic wasps.

Ensliniella parasitica feeds on a circulatory fluid secreted by the wasp called haemolymph and other food stores without harming or offsetting the development of the eggs. On the other hand, parasitic wasps are known to attack the nests of other species of wasps in order to lay their eggs in the cavities of baby potter wasps, eventually triggering their death in order to ensure the success of their species. Until now, the mite was thought of only as a parasite, although Kimiko Okabe and Shun'ichi Makino of the Forestry and Forest Products Research Institute discovered that mites in fact offer protection for the nest.

"None of astigmatid mites, which include this species, were previously known to attack other species, particularly ones larger than themselves," said Okabe, referring to the discovery regarding the mites' behavior.

Experiments in laboratory conditions revealed that as soon as a parasitic wasp enters the potter wasp's nest, the mites attack it and even kill it by inflicting fatal injuries as they cling onto it to feed, something the parasitic wasp is not adapted for. The strategy doesn't always work, sometimes ending with the death of the mites, but in more than 70 percent of the times the parasitic invader is killed, another 10 percent of attacks leading to the certain death of the invader.

Even more surprising is the fact that the potter wasps have special pockets in which they carry their life partners when moving to a new home. The so-called acarinaria usually carries six or more mites, more than enough to fend off an attack, but how this number is maintained in time remains to be found.