Lacy L. Hyche
Leaf-feeding insects are among the most common, destructive,
and often downright annoying pests encountered on shade, ornamental,
and urban landscape trees.Many species are ravenous feeders capable
of completely defoliating trees, thus destroying their ornamental
and environmental values in the landscape. Loss of foliage also
retards tree growth, and may cause dieback in crowns and, in
some cases, tree mortality.
AAES research on tree insects
has identified many leaf feeders associated with Alabama trees.
Among the most destructive and annoying of these are caterpillars,
the larvae of moths and butterflies. Typically, populations of
these leaf feeders vary over time, both in species and in number
of insects present. Commonly, a species will be abundant for
one, two, or three seasons, then scarce for several seasons.
Several species, however, are more common than others, and infestations
tend to occur more frequently. The following presents some of
the more common species found on trees in the urban forest landscape.
Yellownecked caterpillar, colony of young larvae (red color
The yellownecked caterpillar occurs commonly on oaks but will
feed on several trees and shrubs, including apple, basswood,
birch, honeylocust, and maple. The larvae typically feed in colonies,
defoliating one branch, then moving as a group to another. Young
larvae are basically red with yellow or white stripes; the full-grown
larva is about two inches long, black with similar longitudinal
stripes, and has a yellow collar or "neck" behind the
head. Caterpillars are normally present from late July or early
August until mid-October. There is only one generation per year.
Walnut caterpillar, group of young larvae (red-purple
The walnut caterpillar is
closely related to the yellownecked caterpillar. Its favorite
food trees are pecan, hickory, walnut, and butternut. Walnut
caterpillars, like the yellownecked, feed in colonies, moving
from branch to branch. Young larvae are red to purplish with
white longitudinal stripes; fully grown larva is black, 2-2 1/4
inches long, and covered with long white hairs. Two caterpillar
broods occur each year, one in late May and June, and one in
late summer (mid-July through September).
Greenstriped mapleworm; early stage larvae
The greenstriped mapleworm
feeds primarily on maple and boxelder. Early and mid-stage caterpillars
feed gregariously; older larvae tend to separate. Young larvae
are yellowish cream with black heads and faint greenish stripes
along the body. The full-grown caterpillar is about 1 3/4 inches
long. The head is cherry red, and the body is yellow-green with
dark green longitudinal stripes. There are two distinctive long,
black spines behind the head and rows of shorter black spines
along the body. Two broods usually occur each year, one during
May-June and another during August-September.
Spiny oakworm; early stage larvae
spiny oakworm is a close relative of the greenstriped mapleworm,
and bears the pair of long black spines typical of this group
of caterpillars. Oaks, as the name implies, are the primary food
trees. Larvae feed in a group until about half grown, then tend
to separate to feed. Like the preceding caterpillars, their color
changes as larvae develop. Young caterpillars are creamy white
to green with black heads; the fully grown larva is brownish
orange, sometimes tinged with pink, and about two inches long.
There is one brood each year. Caterpillars usually begin to appear
in the last half of July or early August, and may be present
until early October.
The fall webworm is one of
the most common leaf feeders. Larvae feed gregariously and are
responsible for the conspicuous silken webs common on host trees
in summer and fall. Larvae and webs are often found on pecan,
persimmon, sweetgum, willow, and mulberry. In most years, populations
are relatively low, but periodically, the fall webworm occurs
in outbreak numbers, as it did in some areas of Alabama
in 1997. During outbreaks, webs become numerous, and are found
on a wide variety of hosts, including the above trees and cherry
(both native and introduced), sourwood, redbud, sycamore, blackgum,
and cypress. Larval activity actually begins in late April or
early May; however, webs are most common in late summer and fall,
thus the common name.
Hyche is an Associate
Professor of Entomology.
Full-grown black race fall webworm larvae
There are two races, or forms,
of fall webworm larvae orange and black. Orange race larvae have
orange heads and orange tubercles on the body; black race larvae
have black heads and tubercles. Full-grown larvae of both races
are about one inch long and thickly clothed with whitish hairs.