Western tent caterpillars basking in sunlight on the trunk of an apple tree. Vashon Island, Washington, 2003. Photo: Karen Ripley/DNR.
Yes, your deciduous trees might have campers! It’s simply the pesky western tent caterpillar
(Malacosoma californicum) ganging up and consuming the leaves. Their favorite trees are alder, willow, cottonwood, and many other types of broad-leaved ornamental and orchard trees.
The caterpillars are currently seen in Island and Whatcom counties. But don’t worry. These creatures are native to Washington and most likely will not kill your trees if they’re healthy.
Tent caterpillar outbreaks are a natural, cyclical event in northwest forests. About every nine years, they rise to noticeable levels, and the populations remain high for about three years. The actual caterpillars are only present for about six weeks each spring, eating the new leaves.
In July and August, there may be clouds of brown tent caterpillar moths flying about, mating and laying silvery masses of eggs on tree twigs. As the moths die, all is quiet until the following spring, when a new generation of hungry caterpillars hatches.
The 1½-inch-long skinny, smooth, orange and black caterpillars are abundant on trees, roads, houses, mailboxes, and just about everywhere, especially as they complete their feeding and are wandering about trying to find protected sites to construct cocoons. They construct noticeable, dark, silky nests for protection from bad weather.
It’s useful to recognize these features of outbreaks: (more…)