Friday, November 30, 2018

Spider Zombies

Spiders are not usually considered social creatures.  Usually you find them alone--spinning their webs or searching for food. But there are about twenty-five social spider species worldwide. One, Anelosimus eximius [photo below] lives in the Ecuadorian Amazon where it lives in large colonies sharing prey and parental duties with colony members. That is until a colony member is victimized by the newly discovered Zatypota wasp. This wasp has a uniquely gruesome method of reproduction: an adult female lays an egg on the spider's abdomen where the larvae hatches and feeds on the spider's body fluids growing larger and slowly taking over the spider's body and controlling its behavior. The zombie-spider leaves its colony--something a normal Anelosimus would never do--to weave a completely unusual cocoon-like web. There it obliviously waits to be killed and consumed by the larvae. The wasp larvae then enters the cocoon built by its deceased slave were it metamorphoses into a fully grown wasp. Gruesome is perhaps an understatement.

There are other examples of wasp parasites on spiders, but these usually involve a solitary species like orb spiders, and the parasitically induced behavior are within the normal behavioral repertoire. But Zaytypota causes spider behavior completely outside the normal. Researchers do not know how the wasp hijacks the spider's brain and body, but suspect that hormones are injected into the spider's system causing it to function differently.  Zaytypota has been observed victimizing large spider colonies where it can be assured of a stable supply of potential zombies.  Nature can be unforgiving in the struggle for survival.