Bagworms AHOY!

 

Bagworm (Thyridopteryx ephemeraeformis)

(By Sean Mullahy, U of I Plant Clinic Student Worker)

The U of I Plant Clinic received a very fun sample in today. What we thought was a bag full of fir samples to be diagnosed, also contained a freshly hatched bunch of bagworms! Bagworms are an extremely common pest of a large number of ornamental woodies, including spruce, fir, locust, pine, sycamore, and so on. Bagworms are one of the easiest pests to identify and remove, but are also one of the least controlled.

A mature, egg filled, bagworm cocoon

Baby bagworms emerge from eggs in their mother’s bag in late spring, after spending the entire winter inside. After the babies emerge they will almost immediately begin to create their own casings from whatever debris they can find. After making their casings they begin their upward climb to begin the ballooning process. Baby bagworms will feed as they climb, and upon reaching the top of their host will spin webbing of two to three feet in length, and swing off the branches of their hosts. This process is called ballooning, and eventually the wind will grab the bagworm to carry it to a new host. The bagworm hopes that this new host will be suitable, but if not they can always balloon again. After landing on a suitable host the caterpillars will begin to feed. They will start on the upper side of leaves, but quickly make their way to the underside. They prefer to feed from the tops of trees down, destroying it in their wake. As they feed throughout the season they will continually add debris to their casings to keep up with growth. Sometime in late August – early September they will reach full maturity, and find a branch to pupate on. 

Tiny, recently hatched larvae fulfilling their destiny to climb ever upwards

Pupation is around the time the bagworm lifecycle gets very interesting. Bagworms construct a large cone shaped cocoons, making identification easy. The bagworm males will emerge as moths after they finish pupating, the females however will finish the rest of their days in the homes they spent the season constructing. The males emerge as black moths with clear wings, and are about 1” in length. These will fly around hunting for female bags to mate with. Once mating has occurred, usually in late September, the female will lay her eggs in the bag. These eggs will remain dormant until the spring when the caterpillars will emerge, eat their mother’s corpse, and then begin the cycle anew. 

Recently hatched baby bagworms taking their first bites off of foliage, and beginning to build their lifelong husk companions

Bagworms are generally easy to control, if proper care is taken. The easiest time for this would be in the fall when bags have formed. Once bags have formed on host trees, they can be plucked off and collected, with burning being highly recommended. This can be before or after males have emerged from their bags, although after will ensure the destruction of eggs. The only problem with this method, however, is that getting to the uppermost branches of hosts can be difficult. It can also be quite easy to miss a large number of them hidden among the branches. So this technique can thin numbers considerably, but is not a method of complete control. Another check can also be done in spring to remove bags before hatching. If spraying is necessary, late spring or early summer, after the larvae have recently hatched is the best time to do so. If insecticide applications are delayed too far, the worms will have become too big for easy control and will most likely survive the application. It is best to get them before they balloon onto other hosts.  

A mature bagworm, in bag.