How a virus turns a caterpillar into a zombie

Ants aren't the only creatures that can be turned into zombies by microorganisms. A virus known as the baculovirus infects
caterpillars and drives them to climb to the top of the plants they live on right before they die (pictured).

The decaying corpses rain more baculovirus on the foliage below, allowing it to infect
future victims. Birds also eat the dead larvae, spreading the virus over long distances.

Now, researchers have revealed how the baculovirus manipulates its hosts in the first place. Publishing online today in Biology Letters, a team shows that the virus alters the way caterpillars respond to light.

Uninfected moth larvae climb up and down their host plants, regardless of light conditions. They never climb so high as to reach the top of the plants; moreover, mature larvae come down to a safe spot at the base of the plant before becoming immobile pupae. But infected
larvae in the presence of light started climbing 3 days after being infected and then climbed almost 35 mm over the next 14 hours.

Infected larvae in complete darkness, however, did not climb as high and died at lower heights. The virus thus makes the caterpillars move toward light, which in turn triggers them to climb up their host plant and die on top.