Tent caterpillars have been observed in North America since 1646. Outbreaks occur approximately every 10 years and sometimes last up to two years. Although they seldom kill the infested tree, tent caterpillars can cause severe damage, often nearly defoliating the entire tree. If the damage is minor, the tree can bud again later in the summer, but if severe enough, it may take up to two years to recover.
Western tent caterpillars tend to be reddish-brown on top and pale underneath. They have a row of blue spots on their backs, with orange spots interspersed in between. The adult moths are orange-brown with yellow lines on the wings.
The adult moth lays its eggs in midsummer and early autumn. The eggs are deposited in dark brown, saddle-like cases which are 2 cm long, contain 150 to 350 eggs, and straddle or encircle twigs of susceptible trees. In the spring, the eggs hatch into young caterpillar larvae that make communal tent webs. The caterpillars mature in four to six weeks, reaching a length of about 2 to 3 cm.
In June to early July, the caterpillars enter the pupal stage of development, encasing themselves in cocoons. The cocoons may be found on tree trunks, fences, debris and beneath sheltered areas such as raised plant boxes. After about 10 days, the adult moth emerges and mates within 24 hours. The female immediately begins to lay eggs for the next spring, producing only one generation of tent caterpillars every year.
The Western tent caterpillar feeds on willow, poplar, apple, plum, cherry and oak. Since tent caterpillars are native to North America, insect parasites and natural predators such as birds and rodents control a certain percentage of the population. However, some means of control may be necessary where infestations are severe.
If an infestation of caterpillars is suspected, a dormant oil spray may be used on susceptible trees in late winter to smother the eggs before they hatch in early spring.
Products which contain methoxychlor, carbaryl, permethrin and resmethrin are registered for control of tent caterpillars. If the tent is within reach, break it open with a stick and direct the insecticide into it. Spraying is most effective in the evening, as the caterpillars return to the nesting area at night. Contact us today.