Fall Webworm, Bagworm and Tent Caterpillars

by Karen Weiland, Advanced Master Gardener

People have nothing on bugs when it comes to using bags and tents for protection while sleeping.  Some caterpillars have similar methods to protect them from the elements and from the voracious appetites of birds.

The Eastern Tent Caterpillar appear early in the season, usually in late April.   You will find their egg masses, which overwinter in this stage, attached Tent Caterpillarto small twigs, and appear as shiny, dark gray foam wrapped around the twig.  The larvae gather at a fork in a tree and build a web-like tent.  Tent Caterpillars like to feed on wild cherry, crabapple, plum and peach to name a few.  One or two colonies can completely defoliate a small tree.  Since this defoliation occurs early in the season, the plant must expend much energy in setting out new leaves thus enhancing the possibility of weakness.  The egg masses are easy to spot in the fall after the leaves have dropped.  Clip them off the twig and crush or dispose of them.  Nests may be hand removed in the spring by scraping it off the tree and onto the ground where they may be crushed or drop the nest into a bucket of soapy water.  Because most caterpillars will be in the nest, late afternoon or early morning is best to remove them from the tree.

The fall webworm appears on trees in late summer and early fall.  Fall webworms enclose leaves and small twigs in their light gray, silky nests which Fall Webwormare usually located at the tips of branches.  These larvae have been known to feed on over 85 different species of trees in the United States.  This pest overwinters in the pupal stage  in the ground but can also be found in the debris of old nests and under loose bark.  The adults emerge from late May into July.  Nests can be pruned out of small to medium trees.  Biological control may take place as over 80 species of parasites and predators have been identified such as wasps, birds, predatory stink bugs and parasitic flies. Keep in mind that insecticidal sprays will be detrimental to the natural predators of the webworms.

bagwormsBagworms pass the winter as eggs and hatch in early June.  Bagworms prefer juniper, spruce, arborvitae, pine and cedar but have been known to attack deciduous trees.  Bagworms mature in late August or early September. The caterpillars feed for about six weeks, enlarging the bag as they grow.  Older larvae strip evergreens of their needles and devour whole leaves of deciduous species leaving only the larger veins.  When abundant they can defoliate a plant and heavy infestations over several years, especially when coupled with other stresses such as drought, can kill that plant.  Bagworm caterpillars make 1 ½ to 2 inch spindly bags which are sometimes mistaken for a pine cone or other plant structure.  If only a few plants are affected, handpicking and destroying the attached bags by placing them in a bucket of soapy water may provide sufficient control.  If an insecticide is needed, the best time to apply it would be in the early stages while the larvae are small, usually in early July.  Young bagworms are hard to see at first.  Look for small upright bags that look like tiny ice cream cones made of bits of plant matter.

As always, Happy Gardening!

More information about gardening and related subjects is available online at http://www.hort.purdue.edu/ext/garden_pubs.html  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.