Ask the Expert: What’s That Up in Your Trees?

This year I am seeing many plants and trees being infested with Bagworm. This is the larval stage (caterpillar) of a moth, and part of the family of the Lepidoptera, which comprises both butterflies and moths. This insect is able to feed on over a 100 different woody plants, attacking both deciduous and evergreen trees.

Bagworm favor narrow needle trees such as the arborvitae (Thuja), fir (Abies), hemlock (Tsuga), juniper (Juniperus), pine (Pinus) and spruce (Picea), however they are found on many other plants. This Japanese maple tree is fully infested with a late stage caterpillar.

At this stage the insect is almost done feeding and by the end of August the majority of the population will be entering into their pupae stage. They will stay in the closed bag for about four weeks, at which time the female will release a pheromone, which attracts the males to her. The female then lays up to a 1,000 eggs into the bag, where they will over winter, hatching the next spring to start the cycle over again.