Hijacking the Food Chain

Some parasites engineer their own delivery. The lancet liver fluke, Dicrocoelium, cycles through a snail, an ant, and finally a cow. It hijacks an infected ant's brain so the ant climbs a grass blade at dusk and clamps its jaws shut, parking itself where a grazing cow will swallow it. The fluke Ribeiroia makes frogs sprout extra legs, leaving them clumsy and easy prey for the birds it needs next.

No designer planned these routes. Each new host began as a dead end that, over time, became a required stop on the parasite's reproductive tour.