A Native Nuisance
by Josh Palumbo, Forest Management Coordinator
I welcome you to The Nature Foundation at Wintergreen’s attempt to bring some nature and knowledge into your home. The Nine Minute Naturalist borrows from NPR’s lovely 90-Second Naturalist podcast. Since we all have a bit more time on our hands, the goal is to take something that is happening out in our environment and stimulate your brain for roughly nine minutes. Don’t let something as “minor” as a quarantine to keep you from learning. I hope you enjoy!
Wintergreen is laden with non-native species producing havoc to our ecosystem. With so many intrusions from distant lands, it is surprising when we find our landscape nuisances to be native to our eastern forests. The native eastern tent caterpillar is currently intruding upon our landscape and forest trees in an unsightly manner. This Nine Minute Naturalist will delve into the biology and methods of dealing with this native nuisance, the eastern tent caterpillar.
The eastern tent caterpillar is best identified by the creamy white stripe running down the center of the back bordered by yellowish-brown stripes on either side of the stripe. The back is also covered with yellow-brown hairs and has an alternating pattern of blue and black spots along each side. The adult moth has a reddish-brown stout body with two pale stripes on each front wing. They can be identified from a distance by their distinct nest. Their white silken nest is built into the crotch of branches and can be seen from quite the distance. It will gradually increase in size until it measures a foot in length. The caterpillars use this as home base, venturing forth as the day warms to feed on foliage. They will return to home base by nightfall. They are relatively picky about which trees they will nest in and feed on. The primary candidates that host the eastern tent caterpillars are black cherry, apple, hawthorn, chokecherry, pear, plum and most other fruit trees in our region.
The life history of the eastern tent caterpillar dictates how we approach control. Adults lay eggs in ring-like circles that encircle small twigs. The egg masses look varnished and are under an inch long. Eggs will hatch about the time the host leaves begin to open in the spring. The feeding and nest making begin at once starting small and enlarging as the caterpillar grows. In 4-6 weeks, they reach maturity, measuring about 2-2.5 inches. At this time, we will find the caterpillars wandering in search of a place to build their whitish-colored cocoon. They will place them on tree trunks, buildings and fences. The adult moths emerge in late June/early July. Each adult will lay one egg mass containing several hundred eggs around the stem of a twig concluding their life cycle for the year.
Although defoliation and webbing are unsightly, eastern tent caterpillars rarely kill a tree, although heavy infestations will cause a lack of growth and increased stress for that year. Being native to an ecosystem usually indicates a coexistence with a host. Native caterpillars such as eastern tent caterpillars and fall webworm may cause stress but rarely cause death in the host species they depend on for next year’s lifecycle. The other bonus when dealing with native species is they have native predators accustomed to feeding on the caterpillars, thus acting as a population control mechanism. Birds are the primary predator for these caterpillars. Species such as robin, blue jays and cardinals, as well as 50 other bird species, serve as primary control agents.
The best human intervention is mechanical control. Scrapping egg masses on low branches before spring will quickly rid the tree of hundreds of potential defoliators. Once hatched, destroying the nests will open them up to death by predators or cold weather. Nests should be destroyed in early morning hours when all the caterpillars are present. Branches can also be pruned off but that also can decrease growth and cause stress. The last option should be chemical application. There are numerous chemical insecticides that are effective against the caterpillars. Chemical control is most effective when the caterpillars and nests are little. Application of residual insecticides is most effective during the day when they are actively feeding. If using chemicals on a fruit bearing tree, make sure the chemical is specifically marked for fruit trees. Once the caterpillar is wandering from the nest looking to pupate, chemical application is ineffective.
While our instinct is to eliminate anything bothering our landscape trees, native species are participating in an ecosystem dependent on their existence. The Wintergreen environment is accustomed to the presence of tent caterpillars and rarely needs the assistance of man to deal with that particular pest. Use prudence and a measured response when dealing with this native species.