Caterpillars

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2. Most of the serious pests which defoliate trees and shrubs are caterpillars, the worm-like larval stage of butterflies and moths.

3. Caterpillars are voracious feeders. When large numbers occur together, they can completely strip the leaves from a tree. Several colonies of the eastern tent caterpillar helped themselves to this wild cherry. Their silk tents can be seen in the branch forks.

4. Eggs of the eastern tent caterpillar are laid in distinctive shiny masses which encircle small twigs. The caterpillars hatch just as leaves begin unfolding in the spring.

5. Their tents, always located in branch forks, get larger as the caterpillars feed and grow.

6. Full-grown caterpillars are 2-1/2 inches long with a white stripe down the back and blue spots on either side. After completing their development, eastern tent caterpillars leave their host tree and wander in search of suitable places in which to spin their cocoons. Inside the cocoons, they transform into moths which mate and lay eggs once again on cherry, apple, and other suitable host trees.

7. The forest tent caterpillar is a closely related species with a similar life cycle, except that they do not produce tents. Individuals can be identified by the series of keyhole shaped spots that run down their backs.

8. Among the caterpillars commonly known as loopers or inchworms, the fall cankerworm, spring cankerworm, linden looper and a few other species are injurious to ornamental trees. Both fall and spring cankerworms have light and dark color forms, and feed at the same time in late April and May. Fall and spring refers to when adults emerge to lay eggs.

9. Cankerworm outbreaks often involve mixed populations of these pests. Such outbreaks commonly cause localized defoliation of elm, apple, oak, linden, and beech trees, . . .

10. . . . but other trees and large forested areas are sometimes affected. Many insect pests go through cycles of abundance. Outbreaks, which commonly last two to three seasons, are generally followed by several years of low populations.

11. The buck moth caterpillar is a good example. Most of the time, this is a rare insect, but during outbreaks, large numbers can cause serious defoliation of oak trees.

12. Many people know the beautiful morning cloak butterfly, but do not recognize its larval form, commonly known as the spiny elm caterpillar. It is an occasional pest of elm and willow. Unlike other caterpillar pests of ornamental plants, this insect has two generations per year. The first generation of caterpillars appears early in the spring, the second in midsummer.

13. Many other leaf feeding caterpillars appear in midsummer. A coat of long, soft, white hairs identifies this member of the summer defoliator group. It is the walnut caterpillar. Clusters of them feed on the leaves of walnut, butternut, hickory, and pecan.

14. The orange-striped oakworm has similar habits. It also appears in midsummer and feeds gregariously. Groups of them defoliate one branch at a time eating all but the mid-vein of each oak leaf.

15. The green-striped mapleworm has a different color pattern and prefers maple over oak, but its life cycle and behavior are the same.

16. Another member of the summer defoliator group is the red- humped caterpillar. A long list of host plants including hickory, dogwood, apple, and rose are attacked by this pest.

17. The azalea caterpillar, on the other hand, confines its feeding mainly to azaleas . . .

18. . . . and the catalpa worm feeds exclusively on the leaves of catalpa trees. During periodic outbreaks, all of these types of defoliating caterpillars can cause unsightly damage to ornamental trees and shrubs on which they feed. Several registered insecticides offer quick effective control if they are applied when the caterpillars are small and damage is not yet extensive. For large shade trees, it is essential to engage a commercial arborist with powerful spraying equipment.

19. Some caterpillars attract attention more from their large size than from the damage they do. This imperial moth caterpillar will be four inches long when full grown.

20. This monster, known as the hickory horned devil, grows up to six inches long. Despite its ferocious look, it is harmless to man and never occurs in large enough numbers to be considered a pest.

21. There are a few caterpillars that should not be handled because of their stinging spines. Contacting the spines of a saddleback caterpillar is every bit as painful as a bee sting.

22. A number of important caterpillar pests hide themselves in various ways while feeding and are never seen exposed on the foliage. Bagworms hide themselves in silken bags covered with bits of their food plant.

23. The caterpillar inside exposes only his head and front legs as it moves and feeds carrying its bag-like house with it. Most often a pest of conifers, this insect will also feed on sycamore, maple, honeylocust, Asiatic elm, and other broad leaved trees. Controls should be applied when caterpillars and bags are small, like the three on the twig in this picture.

24. Females are legless and wingless. They mate and lay eggs without ever leaving their silken homes.

24.1 Males develop into small, brown, free flying moths.

25. Caterpillars which live and feed within large silken webs are called webworms. The large flimsy nests of the fall webworm are a familiar sight along road sides in later summer. The nests grow larger and larger until entire branches are covered.

26. Inside, the fall webworm caterpillars feed and grow in relative safety.

27. Both mimosa and honeylocust are attacked by the mimosa webworm.

28. Boxwood is attacked by the boxwood webworm,. . .

29. . . . Juniper by the juniper webworm,. . .

30. . . . and pine by the pine webworm. Most webworm problems can be easily solved by pruning out the infested branches. Forceful insecticide sprays will also control webworms if they are applied when the nests are small.

31. A few species of caterpillars, known as leaftiers, pull together several leaves and feed inside their private homes.

32. Leafrollers roll up the edges of the individual leaves; most trees and shrubs are not seriously injured by either leaftiers or leafrollers. However, oak leafroller and azalea leaftier can be serious problems.

33. This caterpillar is perhaps the worst insect pest of trees and shrubs in the United States. This is the gypsy moth. Like many of our other pests, the gypsy moth is a foreign insect that was accidentally introduced to this country. Ever since the 1860's, the infested area has been spreading north, west, and south from Medford, Massachusetts. In 1981, the leading edge reached northern Virginia. During the next decade it is expected to spread widely through the state.

34. Adult gypsy moths do not feed. Their sole function is to mate and lay eggs. These are females depositing their fuzzy, buff-colored egg masses on a tree trunk. Scraping off and destroying egg masses before they hatch help to prevent serious defoliation the following spring.

35. Gypsy moth caterpillars are voracious feeders. They have been reported to feed on over 500 different types of trees and shrubs. Oak, willow, apple, poplar, and larch are among their favorite hosts. In addition, pine, spruce, and hemlock are fed upon during severe outbreaks if they are growing near other infested plants. A few plants which are usually avoided include: arborvitae, azalea, cedar, dogwood, holly, locust, sycamore, tulip poplar, and walnut.

36. Gypsy moth eggs begin to hatch on warm days in April. The caterpillars grow rapidly. By early summer, many of them are full grown and ready to transform into moths. At this point, they leave their host tree and search for hiding places in which to pupate. During outbreaks, large numbers wander through parks and picnic areas, across sidewalks and roads, and onto houses and other buildings. The nuisance of these wandering caterpillars is sometimes as much of a problem as the damage they cause to trees and shrubs.

Return to Insects that Feed on Leaves

	2. Most of the serious pests which defoliate trees and shrubs are caterpillars, the worm-like larval stage of butterflies and moths.
	3. Caterpillars are voracious feeders. When large numbers occur together, they can completely strip the leaves from a tree. Several colonies of the eastern tent caterpillar helped themselves to this wild cherry. Their silk tents can be seen in the branch forks.
	4. Eggs of the eastern tent caterpillar are laid in distinctive shiny masses which encircle small twigs. The caterpillars hatch just as leaves begin unfolding in the spring.
	5. Their tents, always located in branch forks, get larger as the caterpillars feed and grow.
	6. Full-grown caterpillars are 2-1/2 inches long with a white stripe down the back and blue spots on either side. After completing their development, eastern tent caterpillars leave their host tree and wander in search of suitable places in which to spin their cocoons. Inside the cocoons, they transform into moths which mate and lay eggs once again on cherry, apple, and other suitable host trees.
	7. The forest tent caterpillar is a closely related species with a similar life cycle, except that they do not produce tents. Individuals can be identified by the series of keyhole shaped spots that run down their backs.
	8. Among the caterpillars commonly known as loopers or inchworms, the fall cankerworm, spring cankerworm, linden looper and a few other species are injurious to ornamental trees. Both fall and spring cankerworms have light and dark color forms, and feed at the same time in late April and May. Fall and spring refers to when adults emerge to lay eggs.
	9. Cankerworm outbreaks often involve mixed populations of these pests. Such outbreaks commonly cause localized defoliation of elm, apple, oak, linden, and beech trees, . . .
	10. . . . but other trees and large forested areas are sometimes affected. Many insect pests go through cycles of abundance. Outbreaks, which commonly last two to three seasons, are generally followed by several years of low populations.
	11. The buck moth caterpillar is a good example. Most of the time, this is a rare insect, but during outbreaks, large numbers can cause serious defoliation of oak trees.
	12. Many people know the beautiful morning cloak butterfly, but do not recognize its larval form, commonly known as the spiny elm caterpillar. It is an occasional pest of elm and willow. Unlike other caterpillar pests of ornamental plants, this insect has two generations per year. The first generation of caterpillars appears early in the spring, the second in midsummer.
	13. Many other leaf feeding caterpillars appear in midsummer. A coat of long, soft, white hairs identifies this member of the summer defoliator group. It is the walnut caterpillar. Clusters of them feed on the leaves of walnut, butternut, hickory, and pecan.
	14. The orange-striped oakworm has similar habits. It also appears in midsummer and feeds gregariously. Groups of them defoliate one branch at a time eating all but the mid-vein of each oak leaf.
	15. The green-striped mapleworm has a different color pattern and prefers maple over oak, but its life cycle and behavior are the same.
	16. Another member of the summer defoliator group is the red- humped caterpillar. A long list of host plants including hickory, dogwood, apple, and rose are attacked by this pest.
	17. The azalea caterpillar, on the other hand, confines its feeding mainly to azaleas . . .
	18. . . . and the catalpa worm feeds exclusively on the leaves of catalpa trees. During periodic outbreaks, all of these types of defoliating caterpillars can cause unsightly damage to ornamental trees and shrubs on which they feed. Several registered insecticides offer quick effective control if they are applied when the caterpillars are small and damage is not yet extensive. For large shade trees, it is essential to engage a commercial arborist with powerful spraying equipment.
	19. Some caterpillars attract attention more from their large size than from the damage they do. This imperial moth caterpillar will be four inches long when full grown.
	20. This monster, known as the hickory horned devil, grows up to six inches long. Despite its ferocious look, it is harmless to man and never occurs in large enough numbers to be considered a pest.
	21. There are a few caterpillars that should not be handled because of their stinging spines. Contacting the spines of a saddleback caterpillar is every bit as painful as a bee sting.
	22. A number of important caterpillar pests hide themselves in various ways while feeding and are never seen exposed on the foliage. Bagworms hide themselves in silken bags covered with bits of their food plant.
	23. The caterpillar inside exposes only his head and front legs as it moves and feeds carrying its bag-like house with it. Most often a pest of conifers, this insect will also feed on sycamore, maple, honeylocust, Asiatic elm, and other broad leaved trees. Controls should be applied when caterpillars and bags are small, like the three on the twig in this picture.
	24. Females are legless and wingless. They mate and lay eggs without ever leaving their silken homes.
	24.1 Males develop into small, brown, free flying moths.
	25. Caterpillars which live and feed within large silken webs are called webworms. The large flimsy nests of the fall webworm are a familiar sight along road sides in later summer. The nests grow larger and larger until entire branches are covered.
	26. Inside, the fall webworm caterpillars feed and grow in relative safety.
	27. Both mimosa and honeylocust are attacked by the mimosa webworm.
	28. Boxwood is attacked by the boxwood webworm,. . .
	29. . . . Juniper by the juniper webworm,. . .
	30. . . . and pine by the pine webworm. Most webworm problems can be easily solved by pruning out the infested branches. Forceful insecticide sprays will also control webworms if they are applied when the nests are small.
	31. A few species of caterpillars, known as leaftiers, pull together several leaves and feed inside their private homes.
	32. Leafrollers roll up the edges of the individual leaves; most trees and shrubs are not seriously injured by either leaftiers or leafrollers. However, oak leafroller and azalea leaftier can be serious problems.
	33. This caterpillar is perhaps the worst insect pest of trees and shrubs in the United States. This is the gypsy moth. Like many of our other pests, the gypsy moth is a foreign insect that was accidentally introduced to this country. Ever since the 1860's, the infested area has been spreading north, west, and south from Medford, Massachusetts. In 1981, the leading edge reached northern Virginia. During the next decade it is expected to spread widely through the state.
	34. Adult gypsy moths do not feed. Their sole function is to mate and lay eggs. These are females depositing their fuzzy, buff-colored egg masses on a tree trunk. Scraping off and destroying egg masses before they hatch help to prevent serious defoliation the following spring.
	35. Gypsy moth caterpillars are voracious feeders. They have been reported to feed on over 500 different types of trees and shrubs. Oak, willow, apple, poplar, and larch are among their favorite hosts. In addition, pine, spruce, and hemlock are fed upon during severe outbreaks if they are growing near other infested plants. A few plants which are usually avoided include: arborvitae, azalea, cedar, dogwood, holly, locust, sycamore, tulip poplar, and walnut.
	36. Gypsy moth eggs begin to hatch on warm days in April. The caterpillars grow rapidly. By early summer, many of them are full grown and ready to transform into moths. At this point, they leave their host tree and search for hiding places in which to pupate. During outbreaks, large numbers wander through parks and picnic areas, across sidewalks and roads, and onto houses and other buildings. The nuisance of these wandering caterpillars is sometimes as much of a problem as the damage they cause to trees and shrubs.