Regarding the nematomorph or similar nematode species in the previous post
Roundworms are so ubiquitous, it's been said that that even if the rest of the world suddenly vanished, you'ld still see where the water, ground, mud, plants and animals were, by the nematodes left behind. If you were good enough you could even tell what species used to be there, by which species of parasitic nematode suddenly finds itself flapping away in the vacuum.
nematodes are one very big reason humans invented crop rotation and your ancestors didn't starve. Nematode diseases of plants build up fast if you don't remove all possible hosts for them, for a year or two.
Of course some nematodes are useful sometimes - above is a lawn beetle, infected with nematodes as a means of biological control.
Less happy are pinworm, hookworm and heartworm. All parasitic nematodes of mammals. You don't want to picture the inside of a whales intestine, unless you like a seething carpet of rock-candy-striped nematodes as thick as your finger, waving at you from the walls. (If you DO want, go to the Tokyo museum - they have a bed-sized section on display) Why not picture one inside your brain, instead? About 30 centimetres long, in there completely by accident, but more then enough to kill you horribly dead and leave a suprise for whoeever's doing the autopsy.
this nematode lived inside a huntsman spider. It's not the only nematode to spend it's childhood inside large terrestrial invertebrate, there's a whole family of them. Even better, there's a whole PHYLUM - the Nematomorpha - that do the same thing. The adults, however, live in running water.
And it was only last year that we figured out how the worm controls it's host to get it close enough to water - it gets them terribly confused when it senses high humidity nearby, stumbling closer, and then erupts out of the host in a shower of blood and makes its escape. Very chestburster.
The one in the photo got it a bit wrong. He found water ok, but it was in the form of a hot cup of tea
here - a gordiid nematomorph emerging from a praying mantishttp://zoo2.zool.kyoto-u.ac.jp/ethol/showdetail.php?movieid=momo041015ns01b&embed=on