Eastern tent caterpillar (ETC) (Malacosoma americanum) silk nests are now large enough and the accompanying defoliation evident enough to be very noticeable in Ohio. The nests are located in branch forks and they reveal that population densities and caterpillar developmental rates vary widely across the state. I've driven long stretches recently without seeing a single nest on trees flanking the highway only to round a curve or top a hill to arrive in an ETC wonderland.
It is not unusual for ETC populations to be highly variable across Ohio and moth populations can fluctuate dramatically from year-to-year with huge numbers and heavy defoliation from the caterpillars occurring during "outbreak" years followed by an almost complete disappearance of ETC. Overall, I'd say we're experiencing low-to-moderate population densities depending on where you're located.
However, I believe we are seeing an unusually diverse range in caterpillar developmental rates that almost supersede the normal north-south variability common for this and other insects. For example, here in southern Ohio, you can find nests with mid-instar caterpillars located near nests that are being vacated by mature caterpillars that are commencing their annual crawl-about in search of protected pupation sites. This range in developmental rates may be connected to the roller-coaster temperatures experienced when eggs were hatching earlier this spring.
Regardless, active nests may still need to be dealt with to avoid heavy defoliation. The caterpillars prefer to feed on trees in the family Rosaceae, particularly those in the genus Prunus, such as cherries. However, nests may also be found on other rosaceous trees including apple, crabapple, plum, peach, and hawthorn as well as non-rosaceous hosts such as maple.
ETC Two-Step Control Method.
Insecticides can be highly effective against ETC; however, their application may also kill bio-allies such as predators and parasitoids that naturally suppress year-to-year populations of this native pest. Setting fire to the silk nests is also effective and has some entertainment value, but the 1,000-plus F temperatures will seriously damage bark, phloem, and cambium beneath the caterpillar conflagrations leading to canker-like symptoms and even death of entire branches. Firing-up nests is strongly discouraged.
If the nests are few and within reach (even with a broom), we recommend applying the highly effective and environmentally responsible ETC Two-Step Control Method. The technique takes advantage of caterpillar behavior: the caterpillars are found cavorting within their silk nests during the day.
The first step involves using your handy digital pest management tool to remove the silk nest along with the caterpillars from the tree. A broom may be used if nests are out of reach. You may consider enclosing your five-fingered collector in a glove because the caterpillars are covered in hairs that may produce irritation in some individuals.
Transfer the nest to a hard surface and apply compression. An alternate name for this portion of the control technique is the "ETC Two-Step Dance." You can also apply five-fingered digital pressure, but remember the caterpillars may have the last laugh if you don't use a glove.
Thus far, no ETC populations have become resistant to this pesticide-free ETC Two-Step Control Method. Plus, this technique qualifies as a recognized management strategy in Integrated Pest Management (IPM) programs.