What we've managed to create here at Chez Brown is an incredibly diverse eco-system in which everything eats and everything gets eaten.
For example, Little Fire Faery found this Tobacco Hornworm on the tomato plants today.
She came running in to tell me that there was a hornworm that was being eaten by maggots. Having read about this sort of thing before, I knew that it wasn't maggots, but rather wasp larvae. The wasp laid its eggs inside the hornworm, and the maggot-looking growths are the pupae of the wasp.
I knew there were hornworms out there, but I've never considered spraying my tomatoes. I'm also pretty lax about trying to pick them off the tomato plants (they actually blend pretty well with the leaves). My girls usually find them, when they're found, and they get fed to the chickens. Personally, I like this approach better. Do nothing, and the wasps take care of the (potential) problem.
Because this hornworm has been parasitized, he will not eat my tomatoes.
And, then, I can eat my tomatoes.
Everything eats. Everything gets eaten.
It's a pretty amazing thing to witness such a huge diverse system on such an incredibly small piece of land.