The Ant and the Blade of Grass

[Lestat]

Daniel C. Dennett likes to tell the story about an ant crawling to the top of a blade of grass. It turn out that the ant's brain can be invaded by a parasitic worm, which need to get into the belly of a cow for survival. Thus (as Dennett puts it), it drives the ant like an all terrain vehicle up the blade of grass so a cow can digest it.

Well, I certainly have a healthy respect for evolution, but just how on earth did this worm evolve to know not only to invade the brain of the ant, but to then have an exact effect on the brain that causes it to climb up the blade of grass? That just seems too big of a stretch for me. Too wide of a gap to be passed on. Btw- I understand the worm doesn't actually "know" anything, but I'm not sure what DOES know. The DNA of the worm?

I have similar questions regarding the behavior of insects... How many times have you seen a spider crawing on the wall and when you went to kill it, it froze. Now I understand that it freezes, because movement makes it more noticable to a predator. Better to freeze. I can somewhat understand a deer or antelope doing this when sensing a lion in it's presence, but only because they have probably seen other deer and antelope (their parents), do it. Even if this was built into their brain through evolution, I could somewhat understand it.

I get how a wing, or spots, or tails evolve (even bi-pedal mammals). It is a gradual yet, beneficial change that gets passed on. But I cannot see how evolution could've hard wired this freezing behavior into an insect's brain. Insects that didn't freeze were eaten. Those that did, survived, but... How did those that survived pass this trait onto their offspring? Maybe I don't understand it, because I'm under estimating an insects intelligence?