Caterpillar Campers

"Spring is my favourite time of the year. My brothers and sisters and I camp out in the woods, surrounded by raspberry shrubs and other fruity plants. We pitch our tent in a vast, open area so that we can bask in the morning sun. Most of the day is spent hunting for delicious food and once we've eaten our fill, we return to our tent to lazily while away the rest of the day. 

Ah, I am truly alive this time of year!"

- A tent caterpillar who would like to remain anonymous

  

The sunny ledge on the mountain

The Poo Poo Point Chirico trail in Issaquah, WA is a short little 3.6 mile trail that nonetheless leaves you quite out of breath by the time you reach the summit. Just before the final steep push to the very top is a little detour to a clearing on the sunny open face of the mountain. The first time we did this hike, sometime in May, we gladly rushed into the clearing and spent several moments being exhausted and trying to catch our breath. It was a while before we noticed the strange clumps of white strands on several of the trees near us. Each clump was about 3-4 inches long and covered with some kind of brown mass.

Distant view of the caterpillar tent

A closer look at the clumps through our trusty binoculars revealed a strange sight. Each white clump was actually an aggregate of scores of tiny little caterpillars, who seemed to be resting on the silky white bed. The caterpillars' heads were swiftly darting in different directions and as my friend remarked, it rather looked as though they were partying in a club. Research I've done since that hike suggests that these social insects are of the western tent caterpillar species, so named because of the characteristic "tent" that large caterpillar families construct in early spring to spend the larval stage of their life cycle. After a busy day of foraging for leaves, the caterpillars return to their silky abode to rest and digest the day's meals. The tent is always positioned in a place where it receives abundant sunlight as a warm body temperature is critical to a caterpillar's ability to digest food. After 6-8 weeks of intense feeding (which gets them nice and fat, no doubt), the caterpillars are ready to leave their childhood home and prepare for the next phase of life - solitude in the cocoons.

When we hiked up the Poo Poo Point Chirico trail again nearly two months later, there were two important differences:

1. The time I took to catch my breath was nearly half of what it was the first time!

2. The caterpillar campers seemed to have finished their spring vacation - the tents were nowhere to be seen!

A close inspection of the hillside uncovered a bunch of little cocoons, hidden in all sorts of unobtrusive locations.

Cocoons containing the metamorphosing caterpillars

Where's the moth?

And even though we couldn't spot the moths themselves, we did find a cocoon with a large hole on one side, suggesting that its winged inhabitant must have escaped not so long ago. I hoped that the elusive moth was flying far and wide, enjoying its incredibly short adult life while searching for its soul-mate. After mating occurs, the female moth deposits a large bellyful of eggs on the branch of a tree and dies soon after, having lived a full life. The males live a couple of days longer but most of the moths die by the time summer wanes. The egg mass, which soon matures into tiny larvae, survives another full year until the next spring, when a new generation of tent caterpillars are ready to take to the campgrounds!