As you walk through the Arboretum this month, keep an eye out for silken, webby tents covering tree branches.
Over the winter, hundreds of eastern tent caterpillar (Malacosoma americanum) eggs encircle tree branches in dark, varnished clumps. Upon spring’s arrival, the eggs hatch, and recently emerged caterpillars migrate to the nearest branch fork together. These tiny caterpillars, identifiable by the prominent white stripe lining their blue, black, and orange bodies, work together to create silk tents in the fork. Apple and cherry trees tend to be their trees of choice, but birch, ash, maple, oak, and a number of shrub species are also common hosts.
These tents are where the eastern tent caterpillars reside during nights, early morning, and cold or wet weather for the duration of their larval life in May and June. During periods of warmer weather and the daytime, they venture outside of their tents to feed on their host’s foliage. Sometimes, caterpillars will completely defoliate their host, causing the colony to migrate and rebuild on another tree or shrub. As they feed more, the caterpillars continue to grow, and often expand their tents to over a foot long.
After around six to eight weeks, the fully grown caterpillars, which can grow up to as long as two and a half inches, begin to leave their tents to build their own cocoons. These cocoons, which are typically around one inch long, house the caterpillars during their pupal stage for around three weeks, after which they emerge as adult moths.
While eastern tent caterpillars’ defoliating capabilities may appear to be a threat to native wildlife, these springtime visitors are actually native to Minnesota! While their host plants may temporarily seem debilitated by the hungry caterpillars, most recover swiftly without any lasting effects. They are even beneficial to the Arboretum’s wildlife: over 60 bird species feed on them, as well as 28 insect predators, frogs, reptiles, and squirrels (study by Minnesota Agricultural Experiment Station).
Next time you see one of these tents in the Arb, remember that they’re home to hundreds of native caterpillars providing a crucial food source for many beloved Arboretum residents!
Rachel Cheung ‘17, for the Cole Student Naturalists
Photo credits: Teaser and on-page- Hannah Marty ’17