Invasion of the Tent Caterpillars

By Carol Pope | Image: Elizabeth Rowlands

For years we’ve looked with appreciation at the brigade of alder trees that guards our house from the noise and distraction of passing traffic. Since 2003, though, the gentle budding up of spring has had us recoiling from these stalwart friends, for hanging from their branches are hoards of transparent webbed tents writhing with black-and-orange caterpillars.

As summer approaches, the nests are near to bursting, with each ballooning occupant moulting its skin four times to accommodate an increasingly robust girth.

Our tallest alders, some 20 metres high, have been barraged with hundreds of these tents, each one seething with 100 or more caterpillars. Multiply that by the number of descendants these creatures will have, and…well, the math is downright scary.

It’s a comfort, though, to hear from our local scientists that the rise and fall of tent caterpillars (Malacosoma californicum pluviale) is cyclical, gathering momentum over a few years, then sharply diminishing because of an increase of such predators as the tachinid fly, which lays its white eggs on the caterpillar and parasitizes it.

Meanwhile, environmentalists claim caterpillars actually do some good. The exfoliation doesn’t cause long-term damage to healthy trees and provides a boost of summer’s light to the surrounding undergrowth, while the steady downpour of caterpillar excretion nourishes the soil. And, while caterpillars with their clumps of irritating hairs are unpalatable to most creatures, with their ensuing summer metamorphosis into stout-bodied brown moths they become delicious fodder for both birds and bats.

Nonetheless, enough was enough for us last year when, weary of competing with siblings over the few remaining filaments of leaves left on our alders, swarms of caterpillars marched or catapulted into our berry and vegetable garden. While handpicking the pests into large buckets, we could hear a sound similar to that of a late-summer shower snapping onto dry leaves – only it wasn’t rainfall, but rather the chomping of thousands of caterpillars.

While we prefer to let nature take its course in a good part of our yard, we decided it would be fair enough to take out those alders overhanging food crops. Once done, however, we were left with this question: What to do with the resulting tree limbs?

Build a funky fence

Hating waste, when we stumbled across a charming student-made bench on display at a local school, we were inspired to build one ourselves, using screws to attach branches (first drilling holes slightly smaller than the screws to avoid splitting the wood) and painting it with a coat of oil-based water seal on completion. Other large branches are still being hammered to a frame to make a funky fence, and remaining scrappy bits are becoming trellises, hurdles and tuteurs for climbing plants. Lots of fun family projects, and a great way to turn a garden problem into a rewarding opportunity!