Are you happy with the large crop of pine cones that have appeared on your arbor vitae and junipers? Better take another look. The evergreen bagworm (Thyridopteryx ephemeraeformis) builds cases that look just like pine cones but actually are their homes, so take a closer look before you congratulate yourself on the prolific crop on your evergreens.
The bagworms in those cute little houses are the larva of a moth.
When young, the bagworms are black and shiny on the top and dull amber on the underside. When fully grown, they are a dirty gray. The adult male then develops into a clear-winged, furry, black moth with a 1-inch wingspan, somewhat resembling large bees, while the female has no wings or legs and remains in the bag.
This bag is made of silk and material such as lichen, sand and soil, and in early fall when the bags are around an inch long, the larvae suspend them from branches, mostly on evergreen trees. The males then leave and seek females by following their scent, or pheromone, to a bag where they mate and then die because they do not have properly developed mouths. The females remain in the bag just long enough to lay hundreds of eggs, and then die and drop to the ground.
In May, the orphaned larvae emerge from the eggs and spin strands of silk that carry them to nearby plants to feed through the summer. If disturbed while on their journey, the larva will retreat back into the bag and hold it closed until the threat has passed. Their feeding on needles and leaves damages the trees and often is not noticed until the infestation becomes serious.
When the larva finds a favored spot, it will begin to build its own case. The silk used to attach it to a branch is so strong it can strangle and kill the branch it hangs from if left in place for several years.
Bagworms are found primarily in the eastern part of the country, although infestations are spreading as they all seem to do and have been found as far west as the Gulf of Mexico.
Arbor vitae and red cedars are favored by the bagworm, but they also settle on juniper, pine, spruce, hemlock, honey locust, apple, maple and sycamore trees. Recently, they have damaged orange trees in Florida.
So what can we do about them?
Some wasps and hornets feed on the larvae, as do woodpeckers and sapsuckers, but additional measures will be needed. Picking off the cases and dropping them into a bucket of soapy water is the simplest remedy, but obviously this will only work for accessible branches.
Spraying with insecticides such as carbaryl (Sevin) or acephate will work, but also will kill other insects including butterflies, moths and bees. Bt, an organic control, is somewhat effective and safe to use around children and pets, and pheromone traps will lure the traveling males in, but like Japanese beetle traps, they will also lure them to your yard.
If you have bagworms in trees, be sure to rake and burn any debris under the trees in the fall.
It seems new species of destructive insects are being discovered at an alarming rate these days. Add bagworm attacks to the emerald ash borer, gypsy moth, Asian long-horned beetle as well as the wilts, mildews and rusts that are always with us.
Health insurance for trees, anyone?
Janet Del Turco is a local
gardener and a graduate of the Ohio State University Master Gardener program.
Contact her at: