Silver-Spotted Tiger Moth

Order: Lepidoptera
Family: Arctiidae
Species: Lophocampa argentata

Description and Life History: Well, I was sitting here wondering which pest to write about, and right here, in front of my nose (or at least right outside my window) is a silver-spotted tiger moth. I thought I was too late for this to be a timely ‘pest of the month.’ The silver-spotted tiger moth caterpillar is out right now, munching mostly on Douglas fir but it can occur on true firs and pines too. The larvae of the silver-spotted tiger moth are rather unusual looking. Larvae have dark colored bodies with intermixed tufts of rusty and black hairs. Along the dorsum (the back) there are a series of yellowish tufts. Not many caterpillars out in the early spring look like this, so you shouldn’t confuse this critter with anything else. Larvae are present for a good chunk of the year. They hatch out from eggs in late summer and early fall. Larvae feed in aggregations well into and throughout winter depending on warm temperatures. When springtime comes, larvae spread out and increase feeding activity on the tree’s needles; this is usually when you will see them and their damage. In mid to late June, larvae seek out protected habitats to pupate. The adults of the silver-spotted tiger moth are rather attractive; the wings are brown with white and silver spots. Adults fly and lay eggs from July to August. The eggs are deposited on the foliage of the host trees.

Monitoring: Begin looking for aggregations of silver-spotted tiger moth larvae as early as January. These aggregations usually create a webbed tent to feed in and are isolated to a single branch. It may be difficult to spot that early in the season but continue to look for populations throughout springtime as damage becomes more apparent.

Management: The best IPM approach for managing tiger moths is the ‘do nothing’ method. I don’t want to start building a reputation for being lazy, but the do nothing strategy is very valid in this case. Aggregations of tiger moth larvae usually feed on a single branch. Your tree can tolerate this minimal damage, as unsightly as it may appear. If you can’t tolerate it, go ahead and prune out the infested branch. Make sure you dispose the branch in a way that avoids re-infestation (in other words, don’t lay the pruned branch underneath the tree!). Rarely do silver spotted tiger moths kill trees but we have seen pictures this year showing an unnerving amount of damage to small arborvitae hedges.

Silver-spotted tiger moth larvae have a multitude of natural enemies. Many parasitic flies and wasps attack these larvae and their pupae. Small birds, like chickadees and sparrows, love to feast on the easy prey. Bacillus thuringiensis (commonly known as Bt) is another good natural control for silver-spotted tiger moths. Remember that caterpillar outside my window I was talking to you about? Well, it’s been quite a few days since I first noticed it and it hasn’t moved since. It is sitting at the very tip of the new growth of our fir tree fully exposed to its natural enemies and no one has touched it! Upon close inspection, this caterpillar is a black, mushy-gushy, oozy mess because it is infected by a naturally occurring Bt. Caterpillars, when infected by Bt, commonly head up to the tips of plants when they first become sick. Why? Because the Bt bacteria makes the caterpillar do this. Pretty creepy, huh? I bet you didn’t know that not only is Bt a good natural product for killing bugs but it is also good at caterpillar mind control. Bacillus thuringiensis enters the caterpillar through the mouth during feeding. A toxin produced by Bt reacts with the caterpillar’s gut lining, allowing the bacteria access to the caterpillar’s body cavity. Once inside the blood, the Bt bacteria reproduce rapidly and turn that poor caterpillar into mush. Before the caterpillar turns to mush, somehow the bacteria influences the caterpillar to seek out the higher parts of the plant. When this happens and the caterpillar is liquefied, the juices ooze out of the caterpillar and down to lower leaves and stems. Along with the putrid ooze are the bacteria and they hope that another caterpillar will come along and chew the foliage that they just dripped onto! This is one of the ways Bt naturally disperses. Pretty smart for a single cell.