Caterpillar Camp-out! An observation of tent caterpillars.

     

Image 1. Image of a tent caterpillar taken with
a dissecting microscope in a lab at WWU.

Image 2. A tent caterpillar crawling along a branch in a blackberry thicket.

While walking along the path through Western Washington University’s constructed wetland across the street from Buchanon Towers, I stumbled upon one of Bellingham’s frequently observed larvae, the tent caterpillar. While observing the Lepidoptera larva I was able to really notice the way it moves. Its thoracic legs moved smoothly back and forth in a similar fashion to humans or animals, while its prolegs on its abdomen moved in a fashion that reminded me of an inchworm. 
     This inching motion occurs because the hind legs do not use muscles to move, but liquid hemolymph (Fitzgerald 1995).  I also noticed how the very hind prolegs seemed to stick to one leaf while it was deciding whether or not to stay on a new leaf. This occurs because tent caterpillars have small hairs on their feet, called crochets (Image 3, Fitzgerald 1995). These allow the caterpillar to remain firmly secure while moving.

Image 3. Foot of a tent caterpillar taken with
a dissecting microscope in a lab at WWU.

   

 Towards the end of my observations, I decided to time how fast the caterpillar moves. I timed an average of about 0.4 cm per second, and it was about 63^oF. The speed at which a tent caterpillar can move depends on body length and temperature as these factors affect the number of wave cycles per second (Fitzgerald 1995).

Image 4. Remains of a caterpillar tent.

    






 Tent caterpillars are well identified by their tents. These are commonly constructed up in the trees around the leaves. (Image 4). These tents provide a protected place to spend the evening for many caterpillars. Though the tents are made with large amounts of silk, it is the product of many different individuals, and each only contributes a small amount of silk over a period of time (Fitzgerald 1995).

     After looking into the literature, I also found some interesting information about their vision (Image 5). They have six stemmata on each side of the head that may create a mosaic of light to form an image in the brain (Source 1).The outer layer of the eyes shed with the rest of the body while molting, but the sensory apparatus is retained and enlarged (Fitzgerald 1995). Some studies show that caterpillars scan for dark, vertical lines on light backgrounds, like a tree branch against the sky can see horizontal and vertical stems up to 2-3 meters away (Fitzgerald 1995). Other studies have shown that caterpillars are sensitive to different colors (especially green) and can use the polarization of the Sun’s rays to orient themselves (Fitzgerald 1995).

Image 5. Close up of the eyes of a tent caterpillar.
Taken with a dissecting microscope in a lab at WWU.

     Though I have seen these creatures every year en masse, I never really took the time to get a good look at them. I learned many things through my observations and research and gained a new respect for the complexity of what appears to be such a simple creature.