ugly caterpillar can eat. Oak trees without leaves don't live long, and the Oak Processionary caterpillar did serious damage to British forests in the first three years of its invasion.

What England is doing to prepare

The story of the Oak Processionary Moth in many ways resembles North America's difficulties with the Gypsy Moth. Both are alien species that are completely wrecking forests that they're not native to. And both seem almost unbeatable.

Despite a concerted effort by UK officials to spray the caterpillars shortly after they hatch, the pestilence is spreading. Authorities have tried using pheromone traps to nab the bastards, but the United Kingdom Forestry Commission admits that it has been ineffective:

"Over the past five years it has become clear that the network of pheromone traps has not capturedas many moths as expected, nor has it proved particularly effective at monitoring their spread."

The infestation is so bad that the commission has had to revise its long-standing policy regarding the transportation of flora. As of 2008, no trees can enter the United Kingdom without a special "tree passport," a document that describes the provenance of a plant and certifies that it is free of pests and passengers.

Where do they hang out?

Being named the Oak Processionary moth, you'd expect that these caterpillars like oak trees. They do, but they've also been spotted on birches, hazel trees and chestnut trees. A recent alert by the UK Forestry Commision warns of colonies in west and south London, and Pangbourne in Berkshire. You can spot infected trees between April and August