From New Scientist‘s “Parasites brainwash grasshoppers into death dive“:
A parasitic worm that makes the grasshopper it invades jump into water and commit suicide does so by chemically influencing its brain, a study of the insects’ proteins reveal.
The parasitic Nematomorph hairworm (Spinochordodes tellinii) develops inside land-dwelling grasshoppers and crickets until the time comes for the worm to transform into an aquatic adult. Somehow mature hairworms brainwash their hosts into behaving in way they never usually would – causing them to seek out and plunge into water.
Once in the water the mature hairworms – which are three to four times longer that their hosts when extended – emerge and swim away to find a mate, leaving their host dead or dying in the water. …
Now Biron and his colleagues have shown that the worm brainwashes the grasshopper by producing proteins which directly and indirectly affect the grasshopper’s central nervous system.