For over a century scientists have been observing caterpillars engaging in strange migrations. This condition affects many different species of caterpillar, but the virus specialising in the Gypsy Moth caterpillar has a few extra surprises.
These normally nocturnal creatures would starts venturing out in broad daylight, leaving their normal grazing and reaching up into the open canopy. The change was not a choice, it was forced by an invader. The caterpillars were sick, and a virus was in control.
One single gene has been isolated in the virus which is thought to be the ‘caterpillar control,’ it deactivates the caterpillar’s will to moult, sending the caterpillar on a constant feeding cycle. Making one very hungry caterpillar.
As the virus increases its control the caterpillar spends more time up in the canopy. It has contracted a case of ‘Wipfelkrankheit’ which translates to ‘tree top disease.’ The culprit is a baculovirus, a type of virus which specialises in invertebrates, meaning that vertebrates such as we humans are safe for the moment. This particular virus only affect the Gypsy Moth caterpillar, so other caterpillars need also not worry, the can get tree top disease but the won’t have quite the glorious ending this virus affords it’s victims. Over time the virus converts ever more caterpillar cells to virus, eventually the caterpillar grips onto the leaf and dies. The virus then has it’s fun.
Ever more caterpillar becomes virus, producing a large dose of virus. After the daylight demise, more genes also come to the fore. A specialised set of genes in this particular virus begin to melt the caterpillar corpse, if the body is hanging it will elongate, and in any case the body will split open. The co-author of a study into the virus, Kelli Hoover, said:
“it becomes a pool of millions of virus particles that end up dropping onto the foliage below where it can infect other moths that eat those leaves.”
The macabre finish, a slow explosion as the innards now converted to virus burst out and rain down on the former caterpillar’s associates. A death worthy of cinema. A transformation equally as fantastic, but less appealing than the metamorphosis to a moth.