Spring and Fall Cankerworms

• Occurs late April/early May until June
• Chews smalls holes between veins at first, later chewing leaf tissue except for major veins, and eventually chewing all of the leaves except midvein
• Defoliation typically light to moderate, although it can potentially be severe
• Smooth-bodied, light green to brown, 2 inches long when fully grown; moves in the characteristic looping motion

Cankerworms (inchworms) cause defoliation in shade trees. They are found on elm, apple, hackberry, basswood, oak, boxelder, maple and ash trees as well as shrubs growing beneath heavily infested trees.

Young, newly transplanted, or weak trees have more chances of injury from defoliation. If a tree is defoliated for three consecutive years, the branches of the tree can die, making the tree very weak. Pesticides can be used when the caterpillars are small (around the second week of feeding), for two reasons: to protect trees and to eliminate the presence of cankerworm moths around homes.

Spring and fall cankerworms look very similar. There are slight differences in markings and size between the two species that are difficult to detect.

Adult females of both species are wingless, giving them a spider-like appearance. They are both grayish brown and about 5/16 of an inch long. Males have grayish brown wings and an average wingspan of 1 1/8 inches long.

The larvae also look very similar. Full-grown cankerworms are about 1 inch in length and can vary in color.

Spring cankerworms can be yellow-green to brownish to blackish. A white stripe may run along the side of the body, all the way from the head to the back end of the body. Fall cankerworms range from light green to dark green to black. The two species differ in the number of prolegs (false legs) on the back half of the abdomen. Fall cankerworms have three, but, spring cankerworms have only two prolegs.

Spring and fall cankerworms feed at the same time of year on the same trees causing the same kind of damage.  They feed on buds and expanding leaves right after egg hatch in the spring, and they create small BB-sized holes (about 4.4 mm) in the leaves
as the larvae grow, holes get bigger until all the tissue between the veins is eaten up.

Large numbers of caterpillars spinning to the ground on silken threads, crawling or falling on picnic tables, doors, walks and/or house siding can create an unpleasant environment. This stage lasts for only about a week and cankerworms cannot be controlled at this time. They may also create a nuisance during the spring and fall as moths crawl up the exterior walls of homes. Nothing can be done at this stage to get rid of cankerworms.

Cankerworms chew small holes on leaves. They chew between veins first, then leaf tissue (except for major veins), and eventually chew up all of the leaves (except the midvein). Feeding can cause complete defoliation of a tree. A mature, strong tree can survive one to two seasons of complete defoliation, but more than three years of cankerworm feeding can cause the branches to die.

Information source: https://extension.umn.edu

Cecropia Caterpillars

• Occurs August and September
• Chews entire sections of leaves; defoliation typically is minor
• Light green body with a double row of reddish-orange knobs on thorax behind head; also series of smaller yellow and blue knobs on abdomen; grows up to 4 inches long
• Becomes a large, attractive moth

The cecropia moth caterpillar is the largest larva found in Iowa and is commonly seen in late summer throughout the state. Larvae may be seen feeding on the trees and shrubs where they have spent the summer, or they may be found “wandering” across lawns, sidewalks, and driveways.

The caterpillar is about four inches long and nearly 3/4 inch in diameter. The body color is light green with a fluorescent blue tinge. On the top of the body just behind the head are several pairs of large tubercles that look like red, orange or yellow balls covered with black spikes. Along the rest of the length of the body are two rows of yellow spikes and two rows of light blue spikes.

The cecropia caterpillars feed on a wide variety of trees and shrubs, including wild cherry, plum, maple, willow, boxelder, apple, crabapple, lilac, walnut, elm, birch, and poplar. During their life span of approximately 60 days, the caterpillars can devour a lot of foliage. However, caterpillars usually occur in widely-scattered, low numbers and significant defoliation damage is very unlikely except on very small, newly transplanted plants.

In late summer the caterpillar spins a dirty gray or brown cocoon resembling a pod attached to plant twigs or hung between branches. The cocoon is about four to five inches long and an inch or two wide. The insect remains inside this cocoon all winter and the adult moth emerges the following May. The moth is very large and attractive, though they are seldom noticed because they are active at night. The overall wing color is dark reddish-brown. There are black spots near the outer tips of the forewings and a crescent-shaped spot in the center of each wing. The moth’s body is very plump and is covered with long, rust-red hair.

Information source: Iowa State University

Emerald ash borers

• Chewing damage caused by adults occurs late May to early August
• Chews along the edges of leaves; defoliation is typically minor
• Slender bodied, 1/3 – 1/2 inch long; iridescent green with coppery colored head

Forest Tent Caterpillars or Malacosoma disstria

• Occurs May and June
• Chews entire sections of leaves, sometimes leaving some major veins; defoliation often severe
• Hairs along sides of the body, blue and black with characteristic footprint shaped white markings on top of the body

Forest tent caterpillars in Minnesota attack a number of broadleaf trees and plants like quaking aspens, balsam poplar, basswood, oaks, ashes, birches, alder and fruit trees. Feeding damage by these caterpillars slows down the growth rate of deciduous trees. When target trees are defoliated, forest tent caterpillars may also damage other nearby plants. Damage can be seen on vegetables, fruit trees and other small fruits, and nursery crops.  They are a nuisance when they are found around buildings or on roads.

Feeding by forest tent caterpillars generally does not kill deciduous trees, as they can produce another set of leaves during the same season. Healthy trees can tolerate two to three consecutive years of heavy defoliation. Trees may be killed if the same tree has been heavily defoliated for four or more years, and when trees become stressed, such as during a drought.

Mature larvae may be seen on buildings and in yards when they are looking for sheltered sites. They do not bite people or harm animals or property. Their cocoons on the sides of buildings are very difficult to remove and are a nuisance. If forest tent caterpillars on streets get accidentally crushed, they can make surfaces greasy and slippery.

A large gray fly, Sarcophaga aldrichi, feeds on forest tent caterpillars and its population increases when large numbers of forest tent caterpillars are found. This fly does not bite and is harmless, but is a nuisance since it lands on any object, including people. This insect is very important for ending a forest tent caterpillar outbreak naturally.

Information source: https://extension.umn.edu

Linden Loopers

• Occurs May and June
• Chews portions of leaves; defoliation typically is minor
• Smooth-bodied with reddish brown head, it is patterned black, gray, yellow, with a light colored underside; moves in characteristic looping motion

The linden looper overwinters in the egg stage on host trees. In May, or as soon as the buds begin to open, the larvae emerge and begin feeding on the new foliage. Larvae are light brown to yellow, with a broad, bright yellow stripe along each side, and ten, wavy, narrow black lines along their back. The head may vary from yellow to rusty-brown. By late June or early July, the larvae are approximately 37 mm long and are full grown. They crawl or drop to the ground and tunnel into the soil to pupate. Adult moths emerge in October or November. Male moths have a wingspan of 37- 42 mm. The forewings are a light buff color, marked with two, brown, wavy, transverse bands. The forewings also have a sprinkling of brown dots, and at times, a disk-shaped spot. The hind wings are lighter in color and are marked with a faint, disk-shaped spot. Females are wingless and are approximately 13 mm long. They vary in color from light grey to brownish and have two rows of large, black spots on their back. After mating, the females crawl up the tree and deposit eggs singly or in clusters under loose bark or in crevices on the trunks and limbs. Overwintering eggs are oval and yellowish-brown. In Canada, there is only one generation a year of the linden looper.

The linden looper causes damage by defoliation during the larval stage. Large scale control measures have never been required because of natural control by parasites and diseases.

Information source: http://www.agr.gc.ca

Polyphemus Caterpillars or Antheraea polyphemus (Cramer)

• Occurs August and September
• Chews entire sections of leaves; defoliation typically is minor
• It is pale green with sparse long hairs along top and sides of abdomen; grows up to 3 1/2 inches long
• Becomes a large, attractive moth

Polyphemus Moth Larvae reach nearly four inches in length and appear “pushed together” from the ends, making it accordion-shaped. Larvae are fat, pale green, and sparsely covered with hair which is not harmful if touched. They feed on many trees and shrubs including oak, hickory, elm, maple, birch, apple, boxelder, cherry, chestnut, willow, ash, grape, pine, and members of the rose family. The larval period is 48 to 50 days long. In late summer or early fall, the larva spins a rounded, tough, parchment-like cocoon in the tree or shrub in which it has been feeding. It overwinters in this cocoon and emerges the following spring or summer as a very beautiful adult moth.

A common giant silk moth, the male has a wingspan of nearly five inches and the antennae are large and feathery. The wing color is light brown with a gray dusting on the forewing edges and vertical pink lines near the body. Each hindwing has a larger yellow eyespot in a field of dark blue to black. Small yellow eyespots occur in the center of the forewing.

Information source: Ohio State University

Tiger Swallowtail Caterpillars

• Occurs June to September
• Chews entire sections of leaves; defoliation typically is minor
• It is light green with a pair of blue, black, and yellow eyespots behind its head; smooth-bodied growing over two inches long
• Becomes an attractive butterfly

Information source: http://extension.umn.edu