Eastern Tent Caterpillar (moth)
Malacosoma americanum (Fabricius)
Lepidoptera: Lasiocampidae
Introduction
The eastern tent caterpillar is a native moth documented as early as 1646. The caterpillar larvae are known to defoliate trees. They are considered an aesthetic problem due to their large, unsightly silk tents in trees and shrubs, and for their high populations and mobility as they travel on plants, sidewalks, buildings and roads.
Eastern tent caterpillars, as their name suggests, are found throughout the eastern United States as far west as the Rocky Mountains. Their northward range expands to southern Canada.
Green shading indicates approximate range of the eastern tent caterpillar.
Description and Life Cycle
Eastern tent caterpillars overwinter as eggs in a mass containing 150-350 eggs, and measuring approximately 1" (2 cm) long. Masses have the appearance of shiny, dark foam and are found encircling tree twigs about the diameter of a pencil.
Larvae hatch about the same time as cherry leaves unfurl – it is at this time in late spring to early summer that they become a nuisance and cause damage.
As larvae, eastern tent caterpillars are sometimes mistakenly identified as gypsy moth caterpillars or forest tent caterpillars. Eastern tent caterpillars are about 2- 2 ½" (5-6.5 cm) long in the largest larval stage before pupating, with black bodies that are covered in hairs and sport yellow stripes with rows of oval blue dots on their sides. The distinguishing feature to note is the white stripe running across the length of the back. Gypsy moths and forest tent caterpillars lack this white stripe. Additionally, forest tent caterpillars have white "keyhole" markings down the back.
In this species, caterpillars are social and stay together after hatching. Initially they sun themselves on the egg mass, then move to a branch crotch to spin silk in order to make a white tent. One egg mass group may join a neighboring group to make a large colony that can become over 12" long. The tent provides shelter from adverse weather and heat. During such times, caterpillars remain in the tent and do not feed. When they do leave and migrate from tent to tree to feed, they leave a silk trail as a guide to other caterpillars.
Larvae are fully grown in 4-6 weeks and split from the group to individually search for a location to pupate, settling on both natural objects like trees, or constructed ones like fences. The 1" (2 cm) long, yellowish white silk cocoon is spindle-shaped and pupation lasts 2-4 weeks. Adults emerge in late June to early July.
Unlike the larvae which are very noticeable, adult moths often go undetected due to their short life spans and cryptic, reddish brown coloring. Wings have a diagonal, creamy white stripe and wingspans are between 2-2 ½" (5-6.5 cm).
Soon after emerging, adults mate and females lay eggs in July and August that overwinter as the aforementioned egg mass. Adults do not feed.
There is one generation per year.
Eastern tent caterpillar egg mass (Whitney Cranshaw, Colorado State University, Bugwood.org) |
Eastern tent caterpillar larvae (Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Pennsylvania Department of Conservation and Natural Resources, Bugwood.org) |
 |
|
Eastern tent caterpillar adult (Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Pennsylvania Department of Conservation and Natural Resources, Bugwood.org) |
Eastern tent caterpillar larva (Howard H. Lyons, Department of Plant Pathology, Cornell University) |
Damage
Eastern tent caterpillars do cause damage, but as mentioned earlier, they are also considered an aesthetic nuisance in ornamental trees and shrubs.
Caterpillars feed on leaves and can cause defoliation. Although trees usually recover and refoliate, there may be some crown dieback or slowed growth. A small tree may be completely defoliated by just one or two colonies; however, significant defoliation is limited to major outbreaks which fluctuate, generally on a ten year cycle.
Preferred hosts are wild cherry, apple, and crabapple. They also feed on hawthorn, peach, plum, pear and other members of the rose family (though roses themselves are spared).
Aesthetically, this insect is considered a nuisance due to the movement of larvae and occasional high populations. Caterpillars are found crawling over plants, fences, buildings, streets and sidewalks and are messy when squashed. Their large, frass-filled tents are also an eyesore and may become more exposed from defoliation.
|
|
Damage (G. Keith Douce, University of Georgia, Bugwood.org) |
Damage (Howard H. Lyon, Department of Plant Pathology, Cornell University) |
Monitoring
Late July through early spring is the ideal time to inspect trees for egg masses, which should be removed. Take note that egg masses look similar to black knot fungal disease and may lead to confusion in the field. Also watch for tent-building activity in the spring.
Management
Manual destruction of egg masses and tents is an excellent way to control populations. Be advised that the hairs on caterpillars may be irritating to skin.
Twigs encased by egg masses should be pruned out. Tents can also be pruned out or be destroyed by winding around a stick or with a strong jet of water (the best time to destroy tents is before caterpillars leave to feed). Do not attempt to burn tents as this can cause more harm than good.
Tent destruction has another benefit in that it exposes caterpillars to birds and other natural enemies which can help keep populations in check. Eastern tent caterpillars are parasitized by braconid, ichneumonid, and chalcid wasps.
Other control options are available: Bacillus thuringiensis var. kurstaki is useful in the early spring when applied to young larvae, as is insecticidal soap which should be used when caterpillars are out of tents and feeding on leaves. Take care to avoid applying soaps in unsuitable weather conditions (like hot temperatures) as this can lead to phytotoxicity and leaf damage.
Life Cycle Chart
New York State Pesticide Guidelines from Cornell University
Home Gardeners, refer to Pest Management Around the Home, Chapter 10: Tree and Shrub Pest Management
Commercial Applicators, refer to the Pest Management Guide for Commercial Production and Maintenance of Trees and Shrubs
Actions Based on Growing Degree Days and Plant Phenology Index
GROWING DEGREE DAYS/MONTH |
PLANT PHENOLOGY INDEX |
ACTIONS |
1-49GDD March-Early April |
BEGIN BLOOM: Red Maple, Forsythia, Magnolia, Japanese Pieris, Korean Rhododendron, Rhododendron 'PJM' FULL BLOOM: Red Maple, Star Magnolia, Yew END BLOOM: Witchhazel, Star Magnolia |
1-49/Cherry, Crabapple, and other plants in rose family: Look for and prune out black-brown egg masses encircling thin twigs. |
50-99GDD Late March-Late April |
BEGIN BLOOM: Norway Maple, Serviceberry, Saucer Magnolia, Mountain Pieris, Japanese Flowering Cherry, Bradford Callery Pear FULL BLOOM: Sugar Maple, Forsythia, White Ash, Japanese Pieris, Korean Rhododendron, Rhododendron 'PJM' END BLOOM: Red Maple, Korean Rhododendron, Star Magnolia |
50-99/Cherry,crabapple, and other plants in rose family: Look for and remove egg masses and early tents. |
100-149GDD Late April-Early May |
BEGIN BLOOM: Flowering Dogwood, Scotch Broom, Apple, Carolina Rhododendron, Bridalwreath Spiraea FULL BLOOM: Serviceberry, Eastern Redbud, Silverbell, Apple, Japanese Flowering Cherry END BLOOM: Norway Maple, Saucer Magnolia, Mahonia aquifolium, Yew |
100-149/Cherry, crabapple, and other plants in rose family: Remove tents and larvae by hand or treat with registered pesticide if other controls are not adequate. |
150-199GDD May |
BEGIN BLOOM: Common Horsechestnut, Hawthorn, Vanhoutte Spirea, Common Lilac FULL BLOOM: Flowering Dogwood, Scotch Broom, Purpleleaf Sand Cherry, Beach Plum, Bridalwreath Spirea END BLOOM: Forsythia, Higan Cherry, Carolina Rhododendron, Rhododendron 'PJM' |
150-299/Cherry, crabapple, and other plants in rose family: Inspect for larvae webs and plant injury. |
200-249GDD May |
BEGIN BLOOM: Fuzzy Deutzia, Redvein Enkianthus, Leucothoe, Meyer Lilac FULL BLOOM: Common Horsechestnut, Hawthorn, Vanhoutte Spirea, Common Lilac END BLOOM: Apple, Japanese Pieris, japonica, Japanese Flowering Cherry |
|
250-299GDD May-June |
BEGIN BLOOM: Rock Cotoneaster, Beautybush, Catawba , Black Locust FULL BLOOM: Hawthorn, Fuzzy Deutzia, Redvein Enkianthus, Vanhoutte Spiraea, Common Lilac END BLOOM: Apple, Higan Cherry |
|
800-999GDD Late June-Early July |
BEGIN BLOOM: Goldenraintree, Staghorn Sumac FULL BLOOM: Purple Loosestrife, American Elder END BLOOM: Privet, Japanese Tree Lilac, Weigela |
800-2999/Crabapple, Cherry and other plants in rose family: Examine branch tips for shiny black egg masses and remove. |
1000-1199GDD July |
BEGIN BLOOM: Butterfly-bush, Trumpetcreeper, Sourwood FULL BLOOM: Mimosatree, Goldenraintree, Staghorn Sumac END BLOOM: American Elder, Kousa Dogwood |
|
1200-1399GDD July |
BEGIN BLOOM: Summersweet, Rose-of-Sharon, Chastetree FULL BLOOM: Butterfly-bush, Swamp mallow, Sourwood END BLOOM: Gray Dogwood, Goldenraintree, Staghorn Sumac |
|
1400-1699GDD Late July-Early August |
BEGIN BLOOM: Tree of Heaven FULL BLOOM: Summersweet, Swamp Mallow, Chastetree END BLOOM: Goldencup St. Johnswort |
|
1700-1999GDD August |
BEGIN BLOOM: Panicled Hydrangea, Clematis, Winged Euonymus FULL BLOOM: Tree of Heaven END BLOOM: Summersweet, Bigleaf Hydrangea, Chastetree |
|
2000-2399GDD August-September |
BEGIN BLOOM: na FULL BLOOM: Franklin Tree, Seven-son Flower END BLOOM: Clematis |
|
2400-2999GDD September-October |
BEGIN BLOOM: na FULL BLOOM: na END BLOOM: Franklin Tree, Seven-son Flower |
|
QUICK TIPS (return to top) What to look for
When to look
Where to look
How to recognize damage
What to do and when to do it
Prevention
|
References
Bessin, R. 2004. "Eastern Tent Caterpillar."
Department of Agriculture, Forest Service – Forest Health Protection, Southern Region. "Eastern Tent Caterpillar."
Hyche, L.L. 1996. "The Eastern Tent Caterpillar: A Guide to Recognition and Habits in Alabama."
Johnson, W.T. and H.H. Lyon. Insects that Feed on Trees and Shrubs, 2nd ed. (Ithaca, NY: Cornell University Press, 1991), 168.
Rabaglia, R. and D. Twardus. 1990. "The Eastern Tent Caterpillar."
Shetlar, D.J. "Eastern and Forest Tent Caterpillars and Their Control."
University of Massachusetts. "Eastern Tent Caterpillar."