Evolutionary biologists retrace the history of life in all its wondrous forms. Some search for the origin of our species. Others hunt for the origin of birds.

On Thursday, a team of researchers reported an important new insight into the origin of zombies — in this case, ants zombified by a fungus.

Here’s how it works: Sometimes an ant, marching about its business outdoors, will step on a fungal spore. It sticks to the ant’s body and slips a fungal cell inside.

The fungus, called Ophiocordyceps, feeds on the ant from within and multiplies into new cells. But you wouldn’t know it, because the ant goes on with its life, foraging for food to bring back to the nest. All the while, the fungus keeps growing until it makes up nearly half of the ant’s body mass.