Caterpillars under the big top!

In the spring it’s not unusual to see great big tangles of white webs in the trees. Everyone has an idea about what’s behind these constructions. A lot of people think it’s spiders. But the fact is, these webs are the work of what are called “tent caterpillars.”

What are tent caterpillars?

These are caterpillars that build themselves a silk living space, known as a “tent,” within which they develop in a group of numerous individuals. The web is a highly effective means of defense: it protects caterpillars against parasites (flies, wasps), predators (birds) and bad weather, leaving them the leisure they need to graze on the leaves inside their shelter.

Tent caterpillar species

In Québec, five species of tent caterpillars attack several species of native or ornamental tree. Three of them are very common:

• Eastern tent caterpillars (Malacosoma americanum) and forest tent caterpillars (Malacosoma disstria) develop early in springtime. The former build white silky tents in the shape of a purse, while the latter are content to weave a silk carpet on the trunk of the tree. They leave their silken shelter only to feed on the leaves of branches around them. Caterpillars of the two species, brownish and hairy, stand out through the patches of color present on their bodies. The Eastern tent caterpillars have a cream-colored band, very characteristic, running along the back, with the sides of their bodies displaying blue specks and yellow stripes. The forest tent caterpillars also have blue markings along the sides, but present a series of white keyhole-shaped patches on the back.
• Fall webworms (Hyphantria cunea) are more visible in late summer. Very widespread, they’re generally seen on trees bordering roads and along the edges of forests. They often cover a complete branch, even the top of the tree. Caterpillars in this species don’t leave the tent to feed; instead, as they grow, so does the tent.

The damage

It’s above all the deterioration of the esthetic qualities of the tree that raises concern in many homeowners. The most effective method for eliminating these visitors from the trees in our gardens is still collecting and destroying the tents.