Being Mr. Kenny

Parasites are, generally, hated creatures. They take resources but they never give back. That’s actually the biological definition of a parasite: an animal or plant which takes resources (food, energy, etc) without bringing any benefit to its host.

Sheep’s poo

They are, however, fascinating for biologists. One parasite, Dicrocoelium dendriticum is particularly astonishing. D. dendriticum lives in the gut of sheep, and leaves its eggs in the sheep’s faeces.

This causes a problem for our hardy parasite since sheep don’t go around eating each other’s poo. How can it get back into another host?

The solution is quite amazing. D. dendriticum uses two other animals (snails and ants) in order to get back inside the sheep, where it can grow and lay eggs again.

Luckily for our parasite, snails are quite fond of eating poo. Since the parasite’s eggs are tiny, they also get eaten by the snail when it eats the poo, and the eggs hatch inside the snail. The parasite then clones itself many times, and the clones leave the snail in slime balls.

It just so happens that slime balls are particularly delicious to ants, so when the ant eats the slime balls, it gets infected with the parasite too. The parasite continues to mature inside the ant.

So far so good, but how is the parasite going to get inside a sheep? Generally, sheep don’t eat ants, but they do eat grass, and this is where it gets really clever. At one point during the parasite’s lifecycle, one of the parasites moves into the ant’s head, and attaches itself to the ant’s brain.

Mind control!

Once there, the parasite actually takes over part of the insect’s brain, and changes how it behaves to make it more likely to get eaten by a sheep. It’s the ultimate in mind control!

Normally, ants stay on the ground during the daytime, and go back into their nests when night falls. Infected ants, however, climb to the top of stalks of grass when it starts to get cool in the evening, and cling there until it gets warm again in the morning.

Sheep eat grass pretty much all day, so there’s plenty of time for the ant to get eaten in the morning. The ant gets eaten with the grass, since it’s clamped itself to it, and the parasites are carried all the way back into the sheep’s gut.