A few days ago there was a story in the Herald about an Australian huntsman spider that had been found by NZ's border security workers at Auckland airport. With a legspan of up to 15cm these are not small creatures! And yes, we do have them in NZ as well, but they're a different genus: NZ readers may know them as the Avondale spider. 'Our' version was most famously used – and viewed – in the film Arachnophobia.
I was reminded of that story when my Facebook feed brought up an article, complete with video, about how the Australian spiders are used by parasitic wasps as incubators for their babies. (A photo in the linked article will give you a good idea of just how big both wasps and spiders are.) Once a spider's been paralysed and dragged back to the wasp's nest, its stuffed into the cavity and a single egg is laid in its body. Once hatched, the growing wasp larva eats its paralysed host, avoiding any vital organs until the last minute (after all, no self-respecting larva would want to dine on rotting spider if that were avoidable!).
Many people would probably find this quite gruesome, but it is simply the wasp's natural behaviour, and something that Darwin himself commented on in a letter to Asa Gray in explaining his thoughts on evolution and religion (it's a most interesting letter to read):
I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars.