mourning cloak caterpillars
how do i get rid of them they are killing my hackberry tree.
Hennepin County Minnesota
Mourning cloak caterpillars are known to feed on hackberry, among many other trees, however, they are generally not considered to be serious pests, and seldom reach numbers that would cause significant damage to a host. Even if they eat off many of the leaves, they are likely NOT going to kill the tree. Once the caterpillars are gone, if the tree is otherwise healthy, it should put out new leaves and continue on fine. Mourning cloak butterflies overwinter as adults and lay their eggs in the spring. The caterpillars usually reach full size in May or June and then form their chrysalids and transform into new adults. These adult butterflies will not lay more eggs, rather they "estivate" or rest during the summer, feed on flowers briefly in the fall and then go into winter hibernation. So once your caterpillars have pupated, then there will be no more coming to your tree this year. If your caterpillars are over 2" long, then are nearing maturity and will soon transform and do no more damage. If under 2" they may still need a few more weeks of feeding. You probably don't need to control these caterpillars, as your tree should recover. However, if you really insistant on getting rid of them now and if it is a small tree, you could simply pick off or knock off with a stick all the caterpillars you see, or maybe try spraying the leaves with strong water spray from a hose to knock them off. Insecticides containing Bt (Bacillus thuringiensis), a bacterial insecticide specific to caterpillars should kill these larvae without harming some of the natural enemies that might also be helping to control them. Larger trees are difficult to treat by a homeowner, and you might need to hire a pest control company to apply any sprays. However, larger trees will more likely recover faster and put out new leaves, so probably wouldn't need treating anyway.