FOREST HEALTH - HARDWOOD DEFOLIATORS

Many defoliators eat the leaves of trees, their infestation sometimes reaching epidemic proportions.  Presence of these insects can easily be detected by the summer loss, deformtion, or discoloration of leaves on hardwoods.  Resulting loss of the tree’s food manufacturing ability causes a slowing of timber growth, and in the case of sugar maples, can seriously affect sap production. Hardwoods, however, can usually withstand several years of defoliation without death, although stress can predispose trees to other pests.  Fortunately, epidemics are usually cyclic and the insect boom will collapse through starvation or other natural checks and balances before the forest is irreversibly damaged. Many of these species are moths and wasps.  Red text indicates an exotic pest.

Eastern Tent Caterpillar Forest Tent Caterpillar Fall Webworm Gypsy Moth	Large Aspen Tortrix Leaf Galls Leafminers Loopers	Cankerworms Mourning Cloak Orange-striped Oakworm Skeletonizers	Tussock Moths Uglynest Caterpillar Walkingsticks
Eastern tent caterpillar (Malacosoma americanum), moth/butterfly order: spring time dense webs in, other web-makers include fall/spring cankerworms, fall webworm, and uglynest caterpillar
Hosts: cherries, apples, juneberries, et al.
Forest tent caterpillar (Malacosoma disstria), moth/butterfly order: cyclic, mass migrations can be disturbing to humans, does not form tents, 'key-hole' marks on back midline & blue side lines, early summer
Hosts: most broad-leaved trees, especially aspens and the northern hardwoods
Fall webworm (Hyphantria cunea), moth/butterfly order: incorrectly called a tent caterpillar due to similar-looking web tents, common in late summer & fall
Hosts: apples, cherries, ash, oak, other hardwoods
Gypsy moth (Lymantria dispar), moth/butterfly order: look for parallel rows of blue dots and red dots, hairy caterpillars, large outbreaks can be a nuisance to humans, gypsy moth has not resulted in serious mortality in the UP, female moths are white and at least trice the size of the smaller brown male moths, introduced in 1869 with the hope of producing silk fiber
Hosts: oaks, birches, and aspen are most susceptible, but white pines and eastern hemlocks also attacked
Large aspen tortrix (Choristoneura conflictana), moth/butterfly order: early summer defoliator, somewhat cyclic, eggs are laid in flat disks, larvae are dark green to yellow, black head and tail
Hosts: usually quaking aspen, sometimes bigtooth aspen, balsam poplar, paper birch, willows, and alder
Leaf Galls, true bug order and mites (not an insect): small insects and mites feed on leaves within protective leaf tissue that they cause the leaf to grow, shapes and colors vary
Hosts: most hardwoods, often noticed on maples, willows, and oaks
Leafminers, several taxa: many species and hosts, generally harmless, larvae eat the soft leaf layers between the upper & lower leaf layers, tunneled excavations are common, some are exotics, birch leafminer (Fenusa pusilla) has sporadic outbreaks
Hosts: most hardwood species
Loopers (Geometridae, moth & butterfly order): a kind of inchworm, several species, not typically harmful to forest trees, can have irregular outbreaks with some tree mortality, usually spring feeders, e.g. cankerworms (below), elm spanworm (Ennomos subsignarious), linden looper (below), spanworms, geometers
Hosts: most hardwood species
[elm spanworm, half-wing geometer, linden looper]
Cankerworms, spring & fall (Paleacrita vernata & Alsophila pometaria), moth/butterfly order: inchworms, spring defoliation, fall cankerworms overwinter at adults & eggs, spring cankerworms overwinter as pupae
Hosts: prefers apples & elms, but also defoliates maples, ashes, yellow birch, beech, basswood, cherries, and oaks
[upper images are spring cankerworm, lower images are fall cankerworm]
Mourning Cloak (Nymphalis antiopa), moth/butterfly order: a personal favorite, one of the first butterflies to appear each spring and has a fearsome-looking caterpillar
Hosts: elms, willows, poplars
Orange-striped Oakworm (Anisota senatoria, moth & butterfly order): late summer defoliator, caterpillars about 2 inches long, prominent black antennae, descend to ground in fall to pupate in the soil, adults are in the royal moth group, can be spooky to some people
Hosts: oaks
Skeletonizers (Bucculatrix spp.), most in the moth/butterfly order: generally harmless late season activity, larvae eat all but the veins rendering a 'skeleton' look to the leaf
Hosts: birches, oaks, apples, hawthornes
Tussock moths (many genera & species), moth/butterfly order: larvae have distinctive tufts of hairs with some tufts of different lengths and colors, generally considered 'hairy', woolly bear (Pyrrharctia isabella) adults are tiger moths, white-marked tussock (Orgyia leucostigma) is common and pretty (third image)
Hosts: many species
Ugly Nest Caterpillar (Archips spp.), moth/butterfly order: another common 'web' maker in the spring and early summer, nests are often less dense than those of the eastern tent caterpillar but can be heavily loaded with larval waste
Hosts: cherries and oaks
Walkingsticks (Diapheromera femorata), grasshopper order: not a serious pest of trees but large outbreaks can cause noticeable defoliation, more of a human pest as they drop out of canopies, individuals with thicker abdomens are females
Hosts: scrub oaks, cherries

Image Citations
Spring Cankerworm (1) - James B. Hanson, USDA Forest Service, Bugwood.org
Spring Cankerworm (2) - Jerald E. Dewey, USDA Forest Service, Bugwood.org
Fall Cankerworm (1) - John H. Ghent, USDA Forest Service, Bugwood.org
Fall Cankerworm (2) - Jerald E. Dewey, USDA Forest Service, Bugwood.org
Eastern Tent Caterpillar (1) - Jerry A. Payne, USDA Agricultural Research Service, Bugwood.org
Eastern Tent Caterpillar (2) - Tim Tigner, Virginia Department of Forestry, Bugwood.org
Eastern Tent Caterpillar (3) - Lacy L. Hyche, Auburn University, Bugwood.org
Gypsy Moth (1) - USDA Forest Service Archive, USDA Forest Service, Bugwood.org
Large Aspen Tortrix (1) - William M. Ciesla, Forest Health Management International, Bugwood.org
Large Aspen Tortrix (1) - K.B. Jamieson, Canadian Forest Service, Bugwood.org
Looper (1), Elm Spanworm - Arnold T. Drooz, USDA Forest Service, Bugwood.org
Looper (2), Half-wing Geometer - E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Bugwood.org
Looper (3) Linden - Steven Katovich, USDA Forest Service, Bugwood.org
Orangestriped Oakworm (1), larvae - Herbert A. "Joe" Pase III, Texas Forest Service, Bugwood.org
Tussock Moth (1) - Johnny N. Dell, Bugwood.org
Tussock Moth (2) - Herbert A. "Joe" Pase III, Texas Forest Service, Bugwood.org
Tussock Moth (3) - Gerald J. Lenhard, Louiana State Univ, Bugwood.org
Uglynest Caterpillar (3) - Steven Katovich, USDA Forest Service, Bugwood.org
Walkingstick (1) - David Cappaert, Michigan State University, Bugwood.org
All others - Bill Cook, Michigan State University Extension

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This site created and maintained by Bill Cook, MSU Extension Forester for the Upper Peninsula of Michigan.   Editing and modification is ongoing.  Submit suggestions, questions, and corrections to cookwi@msu.edu or call 906-786-1575.