THE EASTERN TENT CATERPILLAR¹ occurs throughout the eastern United States west to the Rocky Mountains and north into southern Canada.  It is native to the region, and references to it as a tree pest date back to early colonial times of the mid-1600's.

The caterpillar is active in the spring.  It is a foliage feeder and, as the name implies, a web- or tent-maker.  Cherry, apple, and other trees of the rose family (Rosaceae) are the preferred hosts, but larvae have been reported to feed on a variety of hardwoods, including ash, birch, blackgum, oak, sweetgum, maple, and poplar.  The grayish-white silken tents seen in forks of trunk and limb or at junctures of large branches in the crowns of preferred hosts (Photo 1) are constructed by the larvae.  The insect's basic life cycle and host preferences remain essentially the same throughout the range, but the time that caterpillars are active during the spring season varies considerably.  For example, caterpillar development may be complete in Alabama by the time activity begins in Canada.

The eastern tent caterpillar is common and often abundant in Alabama.  It is among the first insects to break winter dormancy and become active in the spring.  The typical webs (Photo 1) are oftentimes familiar sights throughout the countryside during March and April.  Data on this common tent-maker and its activities have been accumulated at the Alabama Agricultural Experiment Station at Auburn over several years.  The following is a description of the insect, and its general habits and seasonal cycle as commonly occurring in Alabama.

EGGS/EGG MASSES (Photo 3) - Individual eggs are cylindrical, about one millimeter long with a diameter of about one-half the length.  They are placed upright in rows on host twigs, and form band-like masses that nearly encircle the twigs -- occasionally, rows of eggs may overlap so that masses completely encircle twigs.  Egg mass and twig are covered with spumaline, a frothy substance secreted by the female; the covering is shiny and gives the mass a varnished appearance.

Twenty-five egg masses on black cherry in Lee and Macon counties were collected and examined.  The average length was 15 mm, range 12-17 mm; and, the average diameter of twigs at the base of egg masses was 3.1 mm, range 2-4 mm.  The average number of eggs per mass (determined for 40 masses was 293, range 200-424.

Typical eastern tent caterpillar egg masses are easy to recognize and usually unmistakable on most hosts.  However, on black cherry, a fungal disease (black knot) causes irregular black swellings on branches and twigs (Photo 4).  When small and on small twigs (Photo 4, inset), these swellings, or knots, may sometimes by mistaken for egg masses.

LARVAE (Photo 5, Photo 9, and Photo 11) - The full-grown caterpillar is 50- 55 mm long.  The head is black and the body is lightly clothed with fine tan to light brown hairs.  There is a light stripe down the midline of the back bordered on each side by reddish-brown lines.  The upper area of the side of the body is mostly black, and has a row of blue vertical bars or spots bordered by tan lines; the lower area of the side is bluish.

COCOONS and PUPAE (Photo 6) - Silken cocoons are thin, white, 22-25 mm long, and usually contain fine yellow or yellowish-white powder inside.  Pupae are dark brown, and 18-22 mm long.

The caterpillars are aggressive feeders, and frequently completely strip host trees of foliage.  Healthy trees usually refoliate and survive, but loss of foliage retards radial growth and may cause dieback in crowns.  In the natural hardwood forests of Alabama, preferred host trees are usually small and scattered, and are not generally valued for timber.  Consequently, the eastern tent caterpillar does not generally cause economic losses of timber, and control in natural stand is not usually necessary.  However, conspicuous webs and leafless crowns resulting from infestations make unattractive scenery in an otherwise greening spring countryside.

While not a threat to timber production in the natural forest, the caterpillar often becomes a serious pest in wooded urban, suburban, and recreational areas.  Here, infestations drastically reduce the environmental and ornamental values of shade trees and the wooded landscape.  In the spring, when infestations are heavy and caterpillars numerous, larvae themselves become a public nuisance as, by natural habit, they crawl about in search of pupation sites or alternate food sources.  In urban and recreational areas, control of the caterpillar may sometimes be desirable.  For control recommendations, contact your County Extension Office.

Apple is one of the favored host trees, and in earlier years, the caterpillar was sometimes a serious pest in orchards.  In commercial orchards of today, regular pest management programs have reduced the caterpillar to minor- or no-pest status.

The insect spends the winter as dormant, first-stage caterpillars in unhatched eggs laid the previous spring.  Onset of hatch varies by year but generally occurs sometime during the last half of February to mid-March, and corresponds to the swelling of leafbuds and start of development of foliage.  Dates of first hatch recorded for ten years on black cherry in Lee and Macon counties  (earliest to latest) are shown in Table 1.  The earliest hatch observed was February 16, 1989;  the latest March 13, 1978.  However, in each of seven of the ten years, larval emergence occurred during the last week of February of first two days of March.

Newly hatched caterpillars are black with several narrow white lines across the back (Photo 7).  They feed first on the spumaline covering on the egg mass then move, leaving fine strands of silk as they go, to feed on new foliage or leafbuds (Photo 7).  The caterpillars feed and develop in colonies, and shortly after hatching, begin construction of tents in crotches of trunk and limb or junctures of larger branches (Photo 8).  Tents are enlarged as caterpillars grow.  This type of tent is characteristic of the eastern tent caterpillar, and distinguishes it from some other common webmakers, for example, fall webworm and poplar tentmaker, which construct webs in or around tree foliage.  Eastern tent caterpillars feed during the day, and remain in tents at night, during bad weather, and when resting (Photo 9).  Molting takes place in the tents (Photo 9).  Larval development lasts 5-7 weeks (usually about six), depending on weather conditions, and in the Lee/Macon County area, usually occurs somewhere within a 10-week period from mid-February through April (Figure 1).

Full-grown caterpillars leave tents and foliage of host trees and scatter in search of suitable sites to spin cocoons and pupate.  During this period, caterpillars are often found resting, and sometimes feeding, on a variety of plants in the vicinity (Photo 11).

Larvae spin silken cocoons (Photo 12) and pupate inside.  Cocoons and pupae are usually found in protected places such as under logs, rocks, debris on the ground, in crevices of bark of trees, and sometimes under the eaves and in cracks of buildings.  Cocoons commonly contain fine yellow or yellowish-white powder.  This powder is reported to possibly cause itching or a similar reaction among individuals with sensitive skin.

The pupal stage lasts 3-4 weeks, with the pupal period usually occurring within a time from early to mid-April into the last half of May.  Time of moth emergence and activity varies from year to year, bur generally occurs within the period from early May to the first of June (figure 1).  This is the oviposition period, with eggs being laid on twigs of host trees (Photo 13) as previously described.  Embryos develop to fully formed first-stage larvae within about three weeks.  Larvae enter diapause (a state of arrested development) and remain dormant inside egg shells until the following spring.  There is only one generation each year.

The caterpillar is active in spring with the specific time varying by location (early in the South and later northward) and from year to year at the same location, depending largely on weather conditions.  In east-central Alabama, moths are active for a short time, generally sometime during the last three weeks of May.  Females lay eggs in band-like masses on small twigs. Embryos develop to first-stage larvae within about three weeks.  Larvae enter diapause and remain dormant within egg shells through summer, fall, and most of winter.

Hatch usually occurs during late February and early March, corresponding to time of start of leaf development.  Caterpillars construct webs and feed for about six weeks, with larval development being over in most years by the end of April.  Pupation occurs in silken cocoons during the period mid-April to mid-May.  Adults emerge within about three weeks to begin a new cycle.  There is only one brood each year.

Infestations occur throughout the countryside, but the caterpillar is most serious as a pest in urban, suburban, and wooded outdoor recreational areas.  Here, unsightly webs and leafless crowns severely reduce the aesthetic and environmental values of shade, ornamental, and other landscape trees, and caterpillars, simply by their presence, often become a nuisance.

Control of the eastern tent caterpillar is not usually necessary, but may sometimes be desirable in urban, suburban, or recreational areas.  If needed, recommendations for control can be obtained from the County Extension Office.

¹Malacosoma americanum (F.).  Order Lepidoptera, Family Lasiocampidae.

Stehr, F.W. and E.F. Cook.  1968.  A Revision of the Genus Malacosoma Hubner in North America (Lepidoptera:  Lasiocampidae):  Sytematics, Biology, Immatures, and Parasites.  U.S. National Museum Bull. 276, 321 pp.  Smithsonian Institute Press, Washington, D.C.

For additional information lhyche@acesag.auburn.edu

To Lacy L. Hyche

To Web Publications

All photos courtesy of Lacy L. Hyche