In late spring and early summer, a plain brown moth lays her eggs on the stem of a tree. She’s a Western Tent Caterpillar Moth (Malacosoma californicum) and this act is the last of her short life.
The cluster of 100-300 eggs is protected from dessication and freezing by a frothy secretion (spumaline) that the mother moth produces from special glands.
Malacosoma californicum female with eggs (photo: Jerald E. Dewey)
The eggs soon begin to develop but do not hatch until early the following spring. After hatching (the entomological term is eclose), the little caterpillars all stay close together and function as a social unit as they feed and grow through the spring.
The group of caterpillars secretes silk to create a web-like structure that we call a tent. The tent is suspended from the branches and twigs of the plant that the caterpillars were born on– the host plant. The caterpillars use the tent as a refuge from cold temperatures and predators. The temperature inside the tent is more stable than that of the surrounding air and can be several degrees warmer.
The caterpillars make forays out of the tent, each one wandering the host plant in search of soft, new leaves to munch on. When a caterpillar finds a good supply of leaves, it eats like crazy, then returns to the tent. It leaves a chemical trail along its path that its siblings can follow to find the new food supply.
All this eating leads to the production of lots of little poo pellets. In the video above, these can be seen as black specks in the silky tent.
Tent caterpillars usually don’t cause any lasting damage to their host plants. On occasion, however, there are population explosions of tent caterpillars and whole forests can be stripped of leaves by the insects. Parasitic wasps and diseases generally keep tent caterpillar populations in check so that these outbreaks are infrequent.
After growing larger and larger for 8 weeks, the caterpillars form cocoons and complete their metamorphosis into adults in about 2 weeks. The adult moths reproduce and the whole life cycle is repeated.
{ 11 comments… read them below or add one }
Hi Ivan,
I’m glad to come across your nice webpage on tent caterpillars, and wanted to check with you about any suggestions on how to control these little guys. I’m Sam Allen, and I work as a technician for our small Ag Science Center farm outside of Farmington, New Mexico. We are growing about 10 acres of hybrid poplar trees (many of which are from clones from the Northwest), ranging in age from 6 to 9 years. We were recently swamped with a big outbreak of (Western?) tent caterpillars on the poplars. Any thoughts on how to control them? I realize that, in many cases, they do not significantly harm the tree, but in our case, many of our trees were nearly completely defoliated. I recently started working here, and I am told that we have had problems with the caterpillars before, but not to this degree. As far as control, I know there are some powerful insecticides that could be used. Plus, I’ve heard that I could put out pheremone traps or even buckets of water (to trick the worms into the bucket). Ideally, I’d like to “nip them in the bud” at a certain stage in their life cycle, to reduce the infestation next year. Thankfully, the worms seems to be disappearing in the past week due to colder temps. Thanks for any ideas, if you can think of any.
Sincerely,
Sam Allen
Hi Sam. My experience with these caterpillars is limited to appreciating them in natural habitats. I’ve only seen them in low density. I don’t have any experience trying to get rid of them.
Hi Ivan,
That’s OK — thanks for your response nonetheless. I think I may try to contact a poplar plantation in the Northwest, to see if they have had any problems with tent caterpillars.
Anyway, the caterpillars seem to be going down in number as it is getting closer to Fall.
Thanks, and nice website.
Sam
PS – By the way, I was thinking this was an email link rather than a posting, so please feel free to shorten/delete my original Post with all its details.
Hello I just picked up a Western Tent Caterpillar
I’d like to keep him a little confused.
I don’t want him to die so Whats the best home habitat?
& how long till he turns to a butterfly?
Yesterday Patrick and I went to the Johnston Ridge Observatory at Mt. St. Helens. On the trail that leads from the visitor’s center, there were scores of these caterpillars, all over the sides of the trail. Fun to watch them dance, and it’s good to know that small black specks were poop! Patrick kept a few of his caterpillars on his hat as we walked the trail.
Dear Mr. Barton,
I enjoy your cute story about tent caterpillars on hiking trail.
I remember in 1958, I kept couple caterpillars in jar and watched them transformed into moths through cocoon stage. It was interesting to learn something about their stages of life.
I used to live in Snohomish long ago where I saw lot of caterpillars since 1951. But when we family moved to Stanwood in the fall of 1959, I did not see them anymore as I miss them very much.
Hi Ivan,
During years of 1950′s, there was lot of outbreads and I saw lot of Western Tent caterpillars of two different kinds ( Western and Forest). When I was a kid, I watched Western caterpillars wiggling and noticed their end hopping.
After I moved to Mesa, Arizona, I started to remember the caterpillar’s end hopping. I planned to fly back to Wash. State for my “vacation” and wanted to see them when I heard a news about outbreak in Western Wash. Unfortunately, they were in cocoon stage by first of July that disappointed me. I want to see caterpillars’ end hopping again and want to thank you for video of them as I am glad to see their ends hopping. I am silly! Because, I think they are so cute with hair wiggling.
Janet
It is late September and I have a rather large caterpiller tent in my English walnut tree. I live in Northwest Washington. I have never seen tent caterpillers late in the fall here before. What is going on?
Hi Erren. The only explanation I can think of is that we have had unusually warm and dry weather in the northwest. This is pretty much the driest period that our region has had in the last 100 years.
http://www.king5.com/news/local/Seattle-to-set-to-hit-record-76-day-dry-stretch-172902461.html?c=n
Hi Erren,
I am curious to ask you….how big the tent caterpillar you saw? Was it more than 2 inches long?
I remembered back to 1050′s, there was lot of caterpillars for years while I used to live in Snohomish, the size of caterpillars were a about 1 1/4 inch long and 1/8 inch thick. I wonder if they are getting bigger and bigger??? I am confused.
Wow!!!! That never hear of that in the fall.
I know of some other caterpillars finding in the dirt and even Wooley caterpillars in the fall.
Unfortunately, I currently live in Mesa, Az. I wish I could see the big tent caterpillar in Wash. State. I love them very much because they are cute with soft hair.