A bagworm crawls on the sidewalk trying to escape its fate.

A bagworm crawls on the sidewalk trying to escape its fate.

Gardening employs euphemistic language to describe some occasionally ugly business. Recently I’ve been engaged in “mechanical removal.” It’s a little gross, but I’m enjoying it. You might too, so I thought I’d share.

In these pages I’ve already confessed to gardening in my pajamas so, dear readers, you won’t be shocked to learn that one morning I went out to collect the paper, discovered our arborvitae (Thuja occidentalis) covered in bagworm cocoons. Clad in robe, pajamas and slippers, I leapt into full-attack gardener mode. Before you judge, let me introduce you to my foe as it may reside in your landscape too.

Bagworms are a common garden pest. While they feed on many different plants they are most often found on the conifers in our gardens. As caterpillars they build cone-shaped bags made of silk and bits of the host plant. The males eventually emerge as small, brown moths and go in search of females. The females build larger cocoons which they never leave. After mating, they lay their eggs inside their pupal cast over winter and hatch in spring to begin their life cycle again.

Each female can lay between 500 and 1,000 eggs, which begin to hatch in May or June. The larvae crawl out, feeding on foliage as they go along, and excrete silken threads which they use to rappel down from the tree tops. Gardeners call this “ballooning,” a happy description of thousands of tree-eating worms raining down from the sky.

The cycle begins again with their building their cocoons, defoliating their host plant and generally making a mess. With enough bagworms, they can do serious damage to a healthy tree, It may take a few seasons, but trees can succumb to bagworms.

While I’m not quick with the garden chemicals, this is one case where their use is really problematic and best avoided. The cocoons bagworms create protect them from predators and render chemical sprays ineffective, so you can only spray when they are in the “ballooning” stage. It’s impossible for me to be that prepared and able to disrupt a bagworm’s flight plan.

That leaves granular chemicals, which are applied on the soil for the plant to absorb. When the caterpillars eat the plant, they absorb the chemicals and die. The problem is any caterpillar that eats the plant absorbs the chemicals and dies. This includes the beneficial caterpillars, the caterpillars that might turn into butterflies, and the bagworm caterpillars that are eaten by birds or fed to their chicks. By disrupting the food web we all suffer. So, please leave the caterpillar-killing chemicals at the store.

That brings me to “mechanical removal,” which sounds only slightly more genteel than “hand picking.” It materializes as pajama-clad me picking the brown cocoons off my arborvitae, throwing them to the ground and giving them a jolly stomp on the sidewalk. Their dead bodies litter the walk near our front door. My cover story with my husband is I’m leaving their mashed bodies for the birds to clean up. The reality is scraping them off the sidewalk seems a sorry way to celebrate my victory. Let’s call this what it is: squish enough cocoons, end of bagworms. Battle won.

Absent from their gardens, Kit and Lise enjoy roaming our region exploring the intersection of horticulture and suburban living. More on Instagram @AbsenteeGardener or email: info@absentee-gardener.com.

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