The AgCenter has gotten several calls the past few weeks about strange-looking bugs eating ornamentals. The culprit turned out to be bagworms, the caterpillar stage of moths in the Psychidae family.
The eggs of the bagworm overwinter in the mother moth's bag and hatch in late spring — right about now. The small caterpillars begin feeding immediately and construct their own silken bag, interwoven with bits of leaves and twigs.
The caterpillars eat plant foliage and will feed on a wide variety of plants, though they usually feed on needle-bearing evergreens such as junipers and cedars. The mild winter has led to increased survival and the population is high in some places.
We’ve seen reports of them feeding on many other plants this spring — even birds of paradise. The small caterpillars may give a window-paning effect to the leaf surface. As the caterpillars grow and molt, they enlarge their bag to accommodate their growth.
Larvae remain in the bags to feed and move about with only their head and legged segments protruding from the front opening. You may see them hanging from your plants, house or mailbox. They will move from plant to plant, eating as they go.
They enter their next cycle, or pupate, in late summer, and usually mate and lay eggs around September.
The female spends her entire life in her case. The winged male emerges and finds an encased female with which to mate.
The male moth is black with clear wings that span about 1 inch. The mated wingless female lays eggs (about 300) in her case and then dies. The adult female bagworm looks like a large caterpillar. The eggs overwinter inside their mother’s case and in spring, it all begins again.
Large bagworm outbreaks can seriously damage or defoliate plants. Control is most effective if employed when eggs are just hatching. Bagworm egg hatching coincides with crape myrtle spring leaf development. Insecticides containing spinosad or Bt (Bacillus thuringiensis) are one of the best choices. Bagworms can also be killed by insecticides containing pyrethroids, malathion or carbaryl (Sevin); however, use of these can sometimes lead to a spider mite outbreak, which would be worse than the bagworms.
Bagworms are caterpillars, so anything labeled for control of caterpillars will control them. You can also pick them off plants by hand and dispose of them.
For a free subscription to the GNOGardening newsletter email GNOGardening@agcenter.lsu.edu. It is packed full of timely articles of local interest and information on planting times, monthly chore list and local aggie happenings. You can also visit the LSU AgCenter website for loads of other free information. Send your gardening questions to GNOGardening@AgCenter.LSU.edu.
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