Are you talking about something you saw on "the trials of life" which I have the book and dvd for?Anyone ever see that weird snail parasite that infects their brains? It sends out pulsing probes that attract birds that get infected and shit out the immature parasite for the snail to eat to get infected. Weird stuff. The snails actually live longer with the parasite than without.
Well anyway, what you're talking about is addressed in the trials of life.
The snails don't live longer though, what they do is stay out longer. Usually when the sun comes up they find somewhere to wait it out so they don't dehydrate, but somehow these parasites (or parasite larva) affect the snail's behaviour and make it continue wandering around out in the open during the day, increasing its chance of having its pulsating parasite filled eyes plucked off by birds.
There's a similar parasite which actually gets in the brains of ants, instead of travelling back to the nest infected ants cling onto grass with their jaws, and rabbits come along and unknowingly chomp them up, helping the parasite reach its destination- the rabbit.
Wierd stuff indeed.