Scientists Discover Gene Behind Melting Zombie Caterpillars

Photos: Michael Grove

Watch out for zonked-out, virus-infected caterpillars melting from above: scientists have discovered a single gene in a caterpillar virus that dramatically alters the molting behaviour of the gypsy moth caterpillar, literally turning them into zombies. Once infected, the caterpillars climb up trees to molt, but instead die and melt in a gruesome fashion, spreading millions of viruses to other caterpillars below. According to Livescience, this strange caterpillar disease was discovered more than 100 years ago. Though it was believed to be caused by a virus, it was not clear which specific genes were the culprit, rendering the host to become a crawling caterpillar virus bomb. But this recent study, conducted by researchers at Penn State University and published in Science, pinpoints the exact gene, called egt. As Livescience describes, the presence of egt interferes with the normal molting behaviour of the gypsy moth caterpillar:

The gene, named egt, interferes with the caterpillar's molting hormone and seems to play a role in the caterpillar's urge to climb.

They discovered this amazing property by infecting caterpillars with a normal baculovirus and the same virus lacking the egt gene. The caterpillars infected with the virus that didn't have egt died at the bottom of specially made enclosures (tall soda bottles) meant to mimic their natural environments. Those caterpillars infected with the virus containing egt died clinging to the top of the bottles [..].


Post-mortem, the caterpillar is still clinging to the leaf and undergoes a natural liquefaction process which melts its exoskeleton. Its body is transformed into goo that contains millions of viruses that eventually drips down, infecting new victims and starting the cycle anew.

Though the virus only infects gypsy moth caterpillars, it doesn't mean that humans aren't affected, as lead researcher Kelli Hoover recounts when her hickory tree became home to a horde of virus-possessed caterpillars:

I needed a hat because there was so much frass, insect feces, raining down out of the tree. I would sit there and watch them march up and down the trunk.

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