Monday, 20 February 2017

A wasp that parasitises other wasps - a ghoulish argument against special creationism

Darwin's statement that he could not see how a loving God could have created  wasps whose larva "grew with the express intention of...feeding within the living bodies of Caterpillars" remains to this day a considerable problem for special creationists who appeal to beauty and elegance in nature as proof of creation. Desperate attempts by special creationists to explain away the problem by declaring that they were designed by God to control insects ignore both the fact that less ghastly methods of insect control (swift predation such as seen by mantises) already exist, and that at least 40,000 species of parasitoid wasp have been described. The creation of one species that plies its trade by laying its eggs within the body of another so that its young can devour the host alive poses serious moral issues. For this to be repeated tens of thousands of times multiplies this dilemma even more so.

The problem for special creationists becomes even more profound when we consider the crypt-keeper wasp, Euderus set. This parasitoid wasp lays its eggs inside oak tree stems inside which another parasitic wasp, the crypt gall wasp is maturing. The crypt keeper wasp is not able to gnaw its way out of the oak tree, so it relies on the crypt gall wasp to do this. The way in which it does this is particularly gruesome.

The crypt keeper wasp larvae eat their way inside the crypt gall wasp, triggering a behavioural change in the crypt gall wasp which gnaws a hole too small for it to use for escape. The crypt gall wasp's head gets stuck in this too-small hole, and then dies. The crypt keeper wasp burrows its way out through the head of the crypt gall wasp, and then to freedom. 

This remarkable discovery is documented in a recent Proceedings of the Royal Society B paper. [1] The authors point out that there are two layers of manipulation going on. The crypt gall wasp manipulates the oak tree to create a protective woody protruberance - the gall - while the crypt keeper wasp manipulates the crypt gall wasp to create an easy way for it to escape from a protective woody environment from which it does not have the strength to escape:
Here we describe a novel case of hypermanipulation, in which the crypt gall wasp Bassettia pallida (a phenotypic manipulator of its tree host) is manipulated by the parasitoid crypt-keeper wasp Euderus set, and show that the host's changed behaviour increases parasitoid fitness. Bassettia pallida parasitizes sand live oaks and induces the formation of a ‘crypt’ within developing stems. When parasitized by E. set, B. pallida adults excavate an emergence hole in the crypt wall, plug the hole with their head and die. We show experimentally that this phenomenon benefits E. set, as E. set that need to excavate an emergence hole themselves are about three times more likely to die trapped in the crypt. [2]
Evolution of course has no problems in explaining this. Special creationists - particularly those that appeal to beauty in nature as evidence for special creation - are forced to explain the creation of something so gratuitously ghastly as creating a wasp that eats its way through the head of another parasitic wasp because it is not strong enough to gnaw through wood. Well over 150 years after he penned his letter to Asa Gray, Darwin's observations on theodicy and the parasitic wasp remain an insuperable problem for special creationism.


1. Weinersmith KL, Liu SM, Forbes AA, Egan SP. 2017 "Tales from the crypt: a parasitoid manipulates the behaviour of its parasite host." Proc. R. Soc. B 284: 20162365.
2. Abstract of reference 1.