Photo Gallery
Forest tent caterpillar egg
mass covered by spumaline.
Egg mass which has hatched.
First to third instar FTC
larvae.
Second to third instar FTC
larvae.
Top view of FTC larva
illustrating the keyhole-shaped, white markings.
FTC larva killed by a naturally occurring virus.
There is only one generation annually, which overwinters as fully developed embryos in eggs. Larvae hatch in early spring, usually coinciding with flushing of aspen foliage. The fully mature larvae are 2 inches in length. They are easily identified from other caterpillars by the keyhole shaped spots along their backs, broad bluish lateral bands, and long body hairs. Larvae gather in clusters on their silken mat spun on branches and start their foraging. In five to six weeks, the larvae pass through five larval instars and form silken cocoons to pupate. The stout-bodied moth emerges from the cocoon after about 10 days. the adult moth is light yellow to buff brown in color, with two oblique dark bands on the forewings, and a wingspan of about 1 to 1 1/2 inch. A female deposits 150 to 200 eggs around small twigs and covers them in a frothy substance called spumaline. The embryos develop into larvae in about a month.
Host(s):
Ash, aspen, basswood, birch, cottonwood, elm, maple, oak, poplar, other hardwoods.
Damage/Symptoms:
Defoliation is caused by the larvae. Light defoliation has little effect on tree growth. Two or more years of moderate-to-severe defoliation is necessary to affect radial growth and cause branch and twig dieback. People aslo find the wandering masses of larvae to be extremely objectionable. Unlike other tent caterpillars, extensive webs do not develop.
Comments:
Outbreaks typically last for two to four years in North Dakota. Bacillus thuringiensis, or Bt, is a bacteria toxic to caterpillars. Bt works well to control young caterpillars, while pyrethrins, carbaryl, diazinon, permethrin, and other insecticides are needed to effectively control older caterpillars.
