|MadSci Network: Zoology|
Scientists have a very hard time answering "why" questions- they imply causation, and questions like that are what keeps philosphers busy!
A parent eating his or her offspring is called infanticide or brood cannibalism - and there are a couple of reasons why parents of any species might engage in it.
1. If environmental conditions aren't good (e.g. not enough food around, too cold or too hot), it is very possible that newly born offspring will not survive. In that case, it might be in the parent's best interest to "cut its losses", eat its offspring and get back some of the energy it invested in producing the young in the first place.
2. Many parents do not take care of their young after producing them. So, unless the parent has a way to tell who its own offspring is (something we call kin recognition), it may eat its young by mistake (it is, after all in the parents best interest to eat other parents offspring, because they get a meal out of it, and it gets rid of potential competitors).
I hope that helps!
Rob Campbell, MAD Scientist
Try the links in the MadSci Library for more information on Zoology.