In a perhaps-unprecedented occurrence, Dartmouth's campus has become inundated with bugs, as thousands of caterpillars have emerged to swarm the walls of Dartmouth Hall, block entryways and drop from the trees onto the heads of unsuspecting students.
"I've been here 28 years. I've never seen this happen," said Robert Thebodo, the College's grounds supervisor.
A population eruption of forest tent caterpillars is the cause of the sudden increase in their prevalence in Hanover, biology professor Matthew Ayres said. The natural population dynamics of the forest tent caterpillar include extreme fluctuations, but this is less extreme than it potentially could be.
The cause of population eruptions is unknown. Currently, there is active research -- including research conducted in Ayres' lab -- to try to understand why they happen. One hypothesis Ayres has is that a sequence of favorable climatic conditions exists that affects the caterpillars or induces the trees to have higher quality foliage. What is known is that these population eruptions have happened for the past 10,000 years, Ayres said.
Besides the forest tent caterpillars, eastern tent caterpillars are also present. The eastern tent caterpillars are here every year, though, and are not part of the population eruption. Forest and eastern tent caterpillars can only be distinguished from each other by the white on their backs. Forest tent caterpillars have key shaped white marks down their backs, while eastern tent caterpillars have a white stripe, Thebodo added.
The major threat from forest tent caterpillars is defoliation. In the Northeast, according to the U.S. Department of Agriculture, the favored hosts are sugar maples and aspens, but the caterpillars are not restricted to those two types of trees. With the right numbers, Ayres said, forest tent caterpillars have the ability to defoliate tens of thousands of acres of forest, though the numbers Dartmouth is seeing are not enough for that. Here, numerous trees have been partially defoliated, but none are completely leafless.
Additionally, while defoliation is detrimental and weakens the tree, it happens in early spring and the tree has the entire summer to recover for the next year.
"It is a cool natural history phenomenon that we are seeing, but not a cause for alarm," Ayres said.
These caterpillars are not dangerous and do not sting or bite, unlike other caterpillars.
While the caterpillars may not be a danger, Facilities Operations and Management is still working to remove them because of the detriment to the trees, their inconvenience on the buildings and because they simply look bad, Thebodo said.
FO&M has been monitoring trees since the appearance of the caterpillars to see which trees are most heavily infested. With the bad trees, workers will take backpack sprayers and spray the trees early in the morning with a pesticide specifically for tent caterpillars. Next week, he said, FO&M plans to begin injecting the trees with pesticide.
Even though caterpillars have been spotted inside both Dartmouth Hall and Baker-Berry Library, spraying buildings is not an option, Thebodo said. While FO&M has a license to spray the trees, they do not have one to spray buildings, and due to the risk of pesticides to people, do not even want that license. There are other attempts to remove them from the buildings though.
"We used a hose with just water to wash Dartmouth Row," Thebodo said. "The buildings look cleaner than before, but the caterpillars are returning quickly. I'm hoping not as bad, but that will remain to be seen."
Students have had mixed reactions to the insects. Some squeal in horror at their sight and others see them as an amusement.
"Zach Supalla ['07] and I actually raced them. Mine won despite its detour to scale a blade of grass," Wesley Milks '07 said.
The caterpillars will not be around for much longer though, Ayres said. With the recent warm temperatures, he expects that they will pupate and become moths within the next one to two weeks.
Once the caterpillars become moths, they have a short and relatively uneventful life. They do not feed at all and will live for perhaps a week. In that time, however, they will lay the eggs for next year. Due to the amount of moths laying eggs, Ayres said that there are likely to be 10 times more caterpillars next year.
"Perhaps next year we'll be fortunate enough to witness a spectacular defoliation in the area," Ayres said.
But the eruption should only last two to three years, he added. After that, density dependant effects will cause the population to crash and it will be rare to find one. Causes of a population crash include pathogens, birds or other insects such as wasps. Trees that are defoliated will also typically produce leaves the next year that have more defenses in them and are therefore a lower quality food for the caterpillars.
But until the caterpillar population decreases naturally, College officials will continue to search for an explanation to the surge.
"I've decided that they are looking for the Moth department. They want to become 'mothmaticians,'" Thebodo said.
