I have 2 large black locust trees which this year for the first time ever, had furry black caterpillars about one inch in length. Now there seems to be a large number of brown moths fluttering everywhere. Any suggestions to get rid of the moths and hence reduce eggs laid and more caterpillars.


Thank you for contacting the Toronto Master Gardeners with your inquiry regarding your black locust tree.

Without a picture of the catepillar it is difficult for us to give you a control for the caterpillars/moths on your black locust tree. I have asked a number of Master Gardeners and the following is a list of potential pests:

  1. Locust Twig Borer (Ecdytolopha insiticiana) In Ontario, the locust twig borer, which attacks black locust and honeylocust, is found only in the southern parts of the province. The adult is a small, ashy-brown moth, and the larva is a reddish to straw-yellow caterpillar about 20 mm long. The moths are present in May and June, and the females deposit their eggs on twigs of locust. The eggs hatch in a week, and the larvae bore for a month in the twigs. When mature, the larvae leave the twigs and drop to the ground where they spin cocoons among the leaf litter and overwinter. There is one generation per year. Locust twig borer larvae produce irregular, oval galls about 50 mm long on small branches. These split open with age and mar the appearance of the trees. In heavily infested areas seedling mortality may be high. CONTROL • Chemical control is difficult. Cut and destroy infested twigs in August before the larvae escape. Rake and destroy leaves in the autumn to kill the pupae.-Common Pests of  Trees in Ontario
  2. Eastern Tent Catepillar –The eastern tent caterpillar, Malacosoma americanum (Fabricius), is primarily a pest of black cherry, apple and crabapple, but will occasionally feed on other deciduous trees, including ash, birch, blackgum, maple, oak, poplar, cherry, peach, plum and pear. Caterpillars hatch in late March or early April from a black, spindle-shaped egg mass that encircles the twig. The egg masses, which are coated with a dark varnish-like substance called spumaline, were laid during June of the previous year. In early spring, the foliage begins to emerge, the small, white, silken nests can first be seen in the crotches of limbs. Caterpillars periodically leave the nest to forage on new foliage during the day, leaving trails of white silk wherever they forage. As the caterpillars grow, so does the size of the nest. The caterpillars are black, somewhat hairy and have a white stripe down the back. A series of blue spots are located on each side between longitudinal yellow lines. When mature, the nearly 2-inch caterpillars move down the tree trunks to spin their white, silken cocoons on the bark of trees, on buildings, in grass and in other sheltered locations. The caterpillars can be quite noticeable as they cross sidewalks, driveways and highways prior to spinning their cocoon and pupating. The moths, which emerge in about three weeks, are cinnamon brown with two whitish stripes running obliquely across the forewings.
  3. Fall Web Worm (Hyphantria cunea) webbed masses of yellow-brown, fuzzy larvae with dark heads feeding on leaves of deciduous trees and shrubs.are starting to become more numerous already this year.  Look for larval nests on deciduous trees such as Juglans, Betula, Fraxinus and Prunus.  This year we are seeing them on several other atypical hosts and in much more plentiful numbers than we usually see in July.  Just like other insects, Fall Webworm larvae have boom and bust periods in their life cycles.  Larvae can be found feeding on foliage inside the strong webbing.  Larvae are light yellow with dark spots and will flick their abdomens conspicuously when a predator approaches.  Where possible, manually remove webbed larval masses and destroy them.
  4. Gypsy Moth when young are susceptible to the biocontrol Bacillus thuringiensi . Homeowners can manually destroy Gypsy moth larvae hiding in bark crevices of tree trunks during the heat of the day. Sticky tape is recommended to prevent the moths from laying eggs in the bark.  It is too late to deal with larvae as most have now become moths.  There are pheromone baited sticky traps to reduce the population of adult males (they are attracted to the sticky surface). Gypsy Moth , Gypsy Moth control

You may also wish to consult an arborist. To find a certified professional arborist visit the Ontario branch of the International Society of Arboriculture here.