Western Tent Caterpillars

Kalie Larkin Plant Care Leave a Comment

We actually have several types of tent caterpillar here in Southeastern Idaho. They are considered a simple pest due to the fact that they all have similar life cycles, habits and even appearances. Malacosoma californicum, otherwise known as the western tent caterpillar is the one that is the most common and consequently the most damaging. Their presence is normally more of an eyesore than anything else but can be damaging to previously weakened trees or when there is a large population for several years in a row.

The “host” refers to the plant or plants that the pest in question utilizes throughout its lifecycle. Whether or not it singles out one or many types of plant material is entirely dependent on the pest itself. In the case of our tent caterpillar I like to think of it as the type that does not discriminate. It can be found in quaking aspens, chokecherry, crabapple, willows, cottonwoods, poplars etc. Tent caterpillars have also been seen in multiple types of shrubs: nine-bark, serviceberry, wild rose, sumac etc.

Life cycle
Eggs: are laid during the relatively brief life-span of the adult caterpillar’s final form. They are laid in small masses that have a grey brown coloring and will be found wrapped around twigs about ¾ of an inch thick or less. There can be anywhere from 150-300 eggs in each mass. Luckily each female will only lay a single mass during her lifetime.
Larva: hatch out of their eggs and move towards the branch attachments in early spring right around bud-break. This is when you will see those silken white “tents” go up. These tents will enlarge as the larvae grow, rest and molt inside. They will become fully matured larvae in about a month to month and a half depending on weather conditions. These fully matured larvae are also known as caterpillars. They will grow to be about 2 inches long. Its sides are a pale light blue/ grey with a set of parallel yellow stripes going from end to end. There are dark markings that can either resemble triangles pointing towards the opposing sides or can blend together to seem like an additional dark stripe.
Pupa: After reaching full growth the larvae wander away from the “tent” and weave their own cocoon of white silk which is normally covered with a fine yellowish powder. These cocoons can be found on the host plant, leaf debris, mulch or even neighboring plant material. They will stay inside for about two weeks (give or take a few days) before emerging.
Adult: Adults will emerge as a moth around the warmest part of the summer, say late July or early August. These moths will have a wingspan of 1-2 inches wide and will vary in color from a light tan to a really pretty maroon. These moths have an average lifespan of approximately five days. There is only one generation of adults per season.

Western tent caterpillar are foliage eaters and can defoliate an entire tree when there is a high enough population. Defoliation only becomes a major concern in already weakened trees as a healthy deciduous tree is capable of putting out a second set of leaves in one summer. This second set of leaves starts to use up the extra resources a tree stores up and will stunt that seasons growth. A healthy tree can do this for several years in a row before starting to decline whereas this defoliation/ use of resources could be the straw that broke the camel’s back for an already weakened tree.

Control/ Management
Luckily this is one pest that the time they are the most obvious is also the best time to take steps to manage the infestation. Nests can be removed by hand with a stick/ broom, pruned, treated with pesticide or even sprayed out with a hose. When I was a kid my mom used to send us outside with sticks wrapped in cloth to burn them out but I have since learned that this is not considered a good management practice as you can damage the tree more than the caterpillars would have. Unless it is in a high value location (along a street, by a front door/ window) or a multiple nest infestation it is best to try one of the more natural removal techniques (except burning) first.

Damage is generally more of a nuisance than an actual problem for most plant material, as long as it is healthy. The “tents” are obvious but honestly, I am grateful to these caterpillars for giving me a clear signal (at the right time) that they are present. If you would like one of our arborists to come and look at your trees feel free to give us a call at: 208-523-5296.

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