I was pruning and cleaning up along our driveway the other day when I came upon a couple small cedars that were absolutely covered with bagworms! Some were starting to emerge as I quickly picked them off.
I was going to give them to my chickens but I didn’t think they’d show fast enough interest, so I fed them to the fish. One of my favorite ways of getting rid of them is to pick them off and step on them or drown them in a bucket of soapy water. I have a friend who puts them in a zipper bag and then into the microwave for a few seconds. Some cultures might find this a delicacy! A big problem is that when the tree gets too tall to pick them off safely, they’re pretty much home-free.
Many people confuse the bagworm with the webworm but they are not the same. The webworm makes a silken sac around limbs in a tree and the young can all be seen inside. The bagworm, usually most evident in late summer, is larvae hatched in May/June. Look for a dangling, often twitching, bag, almost like an ornament, on the tip of a branch. It’s made up of a tough silk like fiber, incorporating pieces of whatever the caterpillar that lives inside has been munching on. Bagworms usually are spotted on evergreens but are opportunists and will feed on many plants. Inside the bag lives the larvae of a small moth which will eat voraciously until late summer, at which time the bag will resemble a strange 2-inch long pinecone shaped object.
If the infestation is bad enough they can defoliate and kill a shrub/tree. The larvae will fasten itself to a branch and close the opening of the bag to pupate for about a month. Male bagworms will emerge as small black moths with fuzzy antennae and translucent wings while the female remains in the sac, never developing wings, eyes, mouthparts. She emits a pheromone to attract the male, they will mate through a small hole in the bag, and then the female will lay about 1,000 eggs and die. The male also lacks mouthparts and will die shortly after mating. The eggs will overwinter inside the sac, often in leaf litter, before emerging in the spring to start all over again. There is only one generation of bagworms per year — thank goodness.
The control is a bit tricky. Spraying dormant oil early in the spring will kill some. Any other pesticide sprayed onto the bags must be done while the caterpillar is very small and the sac is still permeable. As it grows older the sac becomes tougher and nearly impervious. There are several predatory insects which feed on the larvae, and a few birds find them tasty.
Remember, anything you spray will affect your “friendlies” as well as the intended target, and often this will cause more harm in the long run.
“Good” creatures/insects don’t recover nearly as fast as those of a pest. If the plants of choice are touching each other, such as in a windbreak, bagworms will be harder to detect or treat. A densely foliaged tree must be checked thoroughly and early.
Bagworms are native to North America and pretty widespread. They can feed on over 50 families of evergreens, deciduous, as well as shrubs. They have one generation a year and they manage to be unseen for most of that time. When the larvae hatch in spring and disperse on the wind via a silken thread. Throughout the cycles it grows, makes bigger bags and can survive a long time without food. After the last cycle the larvae will attach the bag to the host plant, with a strong thick silken strand, then it seal the bag. Initial damage may be seen by an observant eye, but it’s usually most visible after the cocooning. A plant may be denuded severely and may die, especially when it’s hit several years in a row.
My caution is, please hand-pick and destroy when you can rather than using chemical controls. Chemicals often negatively affect lives not targeted — especially ones we REALLY need!