The return of the munching menaces | Sowin' the trowel

Just when you thought it was safe to sit under the fruit trees, tent caterpillars have been spotted on the island and they’re getting ready to chomp, chomp, chomp their way through your orchards and landscaping.

Now that I’ve got your attention, take a deep breath and try to relax. Tent caterpillars can be a certifiable pain in the neck, but they don’t spell the end of the world – or the end of your garden.

Western tent caterpillars are the larvae of the moth Malacosoma californicum. On branches of mostly deciduous trees they’ll lay grey masses of eggs that winter over until around first bud break.

That’s when the tiny larvae begin to weave their webby communal homes in the crotches of tree branches.

If your fruit trees are small enough, you can sometimes find the egg cases and remove them before the eggs have a chance to hatch. From July to early spring look for grey, crusty masses encircling small branches or patches on larger branches and scrape them off.

The tents are small and sometimes hard to spot when they’re new, so examine your trees well. They love the local red alder trees, but look for them on fruit trees or any other deciduous trees. I’ve found them on roses, flowering red currants and catoneaster too, so don’t assume they’ll stick to their usual haunts.

They start out small and black, but as they grow they develop a dotted white stripe down the center of their backs with a lot of yellow-gold on either side.

As they plump out to about two inches in length, their tents will also grow to accommodate their expanding girth. Each morning they’ll venture out to feed on the leaves of their host trees and march like army ants across your deck railings and fences.

Only one generation is born per year, but their total numbers will increase and decrease over successive years in anywhere from a three to seven year cycle.

Some years it seems like a plague of biblical proportions with creepy crawlies dotting the grass like dew drops; other years their tents are few and far between.

The weather and temperature can be limiting factors in caterpillar populations, as well as a parasitic wasp that loves to lay its eggs on the caterpillars’ heads.

Even in “plague” years the damage they inflict is usually more of an aesthetic nuisance than a real threat. However, for many people the ick factor alone can be enough to warrant their control

If you can reach the nest, remove it branch and all and dispose of it, or you can squish it.

This is sometimes enough to collapse the colony. If you attack them in the early morning when they’re all still in bed, even better.

If you spray BT, or Bacillus thuringiensis, as a biological control, know that it will kill all caterpillars, not just the ones you want to get rid of. You must spray as much of the foliage as possible because they need to eat a lot of it to get sick and die.

If you decide instead to use a contact insecticide, be sure you’ve read and understand the directions and warnings on the label and spray it only on the tents, and do it in the early morning when you can get them all.

Finally, don’t set the nests on fire while they’re still in the trees.

Admit it, you want to do it. I know you do.


We encourage an open exchange of ideas on this story's topic, but we ask you to follow our guidelines for respecting community standards. Personal attacks, inappropriate language, and off-topic comments may be removed, and comment privileges revoked, per our Terms of Use. Please see our FAQ if you have questions or concerns about using Facebook to comment.

Read the Oct 20
Green Edition

Browse the print edition page by page, including stories and ads.

Browse the archives.

Friends to Follow

View All Updates