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Let the communes commence!

Got tent caterpillars? Good, now just let them be

Why you should ignore, if not admire, the Eastern Tent Caterpillar

Newly hatched Eastern Tent Caterpilars warming in the sun.
Getting ready to build a tent.
The first few layers of the tent.
A large tent from late May 2014.
Even this denuded black cherry survives and refoliates.
Getting ready to pupate, this ETC feeds on Virginia rose.

Mid-May can mean many things on Nantucket; the first days warm enough for the beach, wine festival, baseball season, and flowering fruit trees. Some of us fair-weather bikers are finally bringing our bikes up from the basement to enjoy a ride along one of our gorgeous bike paths. While appreciating the pink and white petals that festoon the path, you may also be cringing at the site of the annual commune commencement. That’s right, it’s Eastern Tent Caterpillar time!

The Eastern Tent Caterpillar (Malacosoma americanum) is a much maligned creature. I know that most people don’t share my enthusiasm for these insects. There are so many products and websites dedicated to ridding your yard of any evidence of the Eastern Tent Caterpillar (ETC) it's no wonder people consider them a nuisance. This article is not only an appreciation on ETC, it is a list of excuses why you don’t have to waste time and money in removing them. Here are some wondrous facts about the Eastern Tent Caterpillar that may have you thinking twice before torching, spraying, or otherwise eliminating them from your life:

  1. You love birds. Do you feed the birds? Have a bird bath? Well, you are getting a bountiful supply of protein free from Mother Nature. Cuckoos, blue jays, and chickadees are known to eat ETC. Despite some old wives tales about being toxic, ecological impacts of ETC are mainly positive!
  2. You like bees, butterflies, buy organic, and eat local. Please don’t spray the trees! Black cherries, crab apples, and beach plums are the primary hosts for Eastern Tent Caterpillars. Spraying them in the spring, when the trees are in bloom, can have detrimental effects on pollinators and nectar-feeding butterflies. Plus, you don’t even need to spray (see #3 below). Remember, tent caterpillars are native and a natural part of our ecosystem. 
  3. Your trees are fine, honest. Healthy deciduous trees usually survive defoliation and grow back a second set of leaves by July. Most trees can even survive two or three defoliating years before they are harmed. It is generally trees that are diseased or otherwise compromised which are susceptible to detrimental effects from an ETC defoliation. Just think, you’ll have fresh, green leaves in July. Everyone else’s leaves will be so passé.
  4. Eastern Tent Caterpillars are cyclic. Like many species of this group, ETC go through regular boom and bust cycles. Therefore, if you think it’s a really bad infestation year, have heart knowing that the population will be diminished next time around. Populations of tent caterpillars reaching highly noticeable levels run approximately on 10-year cycles and usually last 2-3 years. 2015 is the second “big year”, so we may have one more before numbers drop.
  5. Eastern Tent Caterpillars are social insects and amazing at what they do. When ETC hatch, they are half the size of a dime. Regardless of which egg cluster they hatch from, they team up with other ETC on the same tree and begin tent building. They build the tent for protection from predators and the elements. As they get bigger, they add layers daily to the tent. It’s like having multiple floors with the tent as a mini-greenhouse. They thermo-regulate by going up or down “floors”. Look inside a tent sometime and see that they are on different layers depending on the air temperature, direct sun, etc. Let’s all just marvel at the architectural abilities of the ETC!
  6. They work together! When an ETC goes out in search of food, it leaves a silk trail behind it. That way, others know that there is food in that direction. Should that branch become defoliated, the caterpillar simply chews off that thread saying, “Don’t go that way, there’s no more food”. Who needs bread crumbs when you can make your own silk trail?!
  7. ETC can give us insights into climate change. Being particularly sensitive to temperature, we can study the behaviors and timing of ETC over time. The Linda Loring Nature Foundation is monitoring ETC hatch timing in conjunction with the phenology project investigating leaf-out and flowering of some common, native shrubs. Species-specific responses to climate changes could result in alterations to habitats such as our grasslands and heathlands. Instead of a canary in a coal mine, we, on Nantucket, have an Eastern Tent Caterpillar in a heathland.

Alas, all good things must come to an end. Even the best communes succumb at some point. Similarly, the ETC tenting phase comes to an end when everyone is too big for the tent (about six to eight weeks after hatching) and it’s filled with poop. Isn’t that always the way? Sometime in mid to late June the ETC will abandon their tents as they continue to forage and then build cocoons. At that time, feel free to wipe away the old tents from your trees. As you do, you can keep in mind how the ETC amazing architectural achievment is also biodegradable.