By Brice Bartley, Fort Belvoir Directorate of Public Works Natural Resource SpecialistApril 23, 2014
Fort Belvoir, Va. (April 24, 2014) - As spring arrives, many insects and other arthropods emerge. While some of them do bite, sting, chew up prized plants, or fly and crawl where they are unwelcome, it is important to remember that most are beneficial natives, which play important roles within our complex ecosystem.
Such interactions include pollination of plants, consumption of pest species, removal of dead and decaying plant and animal matter and, most importantly for this article, providing food for birds and other wildlife.
These benefits are good to bear in mind when faced with obnoxious insect behaviors, such as those exhibited by the moths known as cankerworms. This term refers to two different species of green inchworms, which go by the common names of spring cankerworm and fall cankerworm. Of the many similarities between these species, one of the most notable is that the adult female moths are wingless, and it is their different periods of emergence and egg-laying, spring and fall, between which their common names distinguish. The larval, caterpillar stage of both species emerge in spring, and this aspect of their life cycle earns them the shared portion of their common name, cankerworm.
These caterpillars can prove annoying with their sticky silk, occasionally overwhelming numbers, and defoliation of trees. The insects use their silk strands for travelling on the wind between trees, but sometimes they land on pedestrians instead. When hundreds of them do so, helping to call attention to the damage that they can do to trees, it understandably can be cause for frustration and concern among community members.
Those concerned with potential impacts to tree health should note that established trees are able to withstand even total defoliation on an occasional basis, and all healthy trees will produce enough leaves to sacrifice some to inevitable insect damage. Although the caterpillar stage of both species lasts for about a month, flocks of birds often will be attracted to high density cankerworm infestations and, within just a few days, dramatically reduce their numbers. Fort Belvoir wildlife officials have noted that cankerworms appear to be an important food source for native birds, which is important to recall when faced by the nuisance posed by them in the spring. In fact, the timing of the cankerworms in the spring coincides with the return of many migratory birds.
Some Belvoir community members may have noticed bands of tar paper on trees in areas adjacent to the installation, and these were traps placed by Fairfax County pest managers in order to monitor cankerworm numbers. While the county does plan to spray some of those areas in the last week of April out of concern for the high numbers of moths detected by those surveys, Fort Belvoir has no plans to conduct any spraying for cankerworms on the installation.