Spring (Paleacrita vernata) and fall (Alsophila pometaria) cankerworm, often called inchworms because of the way they crawl, feed on buds and expanding leaves in the spring.  The larvae’s droppings can also be a nuisance.  Low populations of cankerworms do not cause extensive damage, but high populations can defoliate trees by late spring. 

Cankerworm populations build up over several years and then decline due to environmental causes.  The feeding habits and damage are very similar for the spring and fall cankerworm, but the life cycles are different.

Susceptible Hosts

Cankerworms have a wide host range, but prefer elm (Ulmus), apple (Malus), oak (Quercus), linden (Tilia), ash (Fraxinus), hickory (Carya), hackberry (Celtis), maple (Acer), and beech (Fagus).

Pest
Fall cankerworm (Alsophila pometaria)
Spring cankerworm (Paleacrita vernata)

Symptoms
* Small holes on leaves in spring are caused by young larvae.
* Complete defoliation, except for the leaf veins, may occur by late spring by older larvae.

Signs
The spring and fall cankerworm are very similar in appearance.  They are often called inchworms because of the way they crawl.  They arch their back into a loop and extend the front to move forward.

Fall Cankerworm
* Mature larvae are about 1 inch (25 mm) long and vary from light green to black, with three narrow light-colored lines along each side.
* Adult males are 1inch (25 mm) long and dull grey.  The wing span is about 1 to 1 ½ inches (25 to 37mm) with two wavy stripes on each forewing.  Adult females are wingless and dull grey.  
* Fall cankerworms have three pair of prolegs

Spring Cankerworm
* Mature larvae are 1 inch (25 mm) long and vary from yellowish green to reddish brown, or black.  The head is light and a single yellowish white stripe lines each side of the body.
* Adult males are brownish-grey with three dark stripes across the forewings.  Adult females are wingless and grayish brown with a dark stripe down the back.
* Spring cankerworms have two pair of prolegs.

Life Cycle
Fall Cankerworm
* Adult moths emerge from the soil in fall after a hard freeze, usually between October and December.
* Mating occurs as the females search for small twigs to deposit her eggs on.  Both males and females die after the eggs are deposited.
* Eggs hatch in mid-spring at about the same time as the opening of elm buds.
* Larvae feed on leaves for about four weeks before dropping to the ground to pupate in the soil where they will emerge later in the season as adults.

Spring Cankerworm
* Adult moths emerge in early spring
* Eggs hatch in mid-spring at about the same time as the opening of elm buds.
* Larvae feed on leaves for about four weeks before dropping to the ground to pupate in the soil where they will emerge the next spring as adults.

Distinguish from look-alikes
Proper identification of the host plant, timing of symptoms, and particular marking characteristics are key distinctions between caterpillars.

Distribution
The spring and fall cankerworm ranges throughout the eastern U.S south to North Carolina, Arkansas, Texas, and as far west as Montana, Colorado, Utah, and California.

Cankerworm control is not always needed.  Healthy trees can withstand extensive defoliation since cankerworm damage is done early in the spring and trees have the chance to leaf out again.  Control is recommended for new transplants, high valued specimen trees, or fruit and nut bearing trees.  Trees that have a previous history of stress such as defoliation, drought, or disease should also be treated.  Trees should be confirmed with larvae and damage before treatment is necessary.

Chemical treatment is most effective in the second week of feeding after egg hatch.  Damage is minimal and caterpillars are still small at this time, so close inspection is needed.  During the third and fourth weeks after egg hatch, cankerworm damage becomes extensive and very noticeable.  Treatment is not effective at this time because the damage is already done.

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