A student reached down with a pair of forceps and carefully removed an insect from the nostril of the pig snout sticking out of the dirt.
Working with blue-gloved hands, she deposited the bug into a small, clear collection vial, capped it and took a closer look.
"What is that?" she said.
"I don't know," said Holyoke Community College professor Elizabeth Butin, "but we'll find out."
The prior week, Butin and her students had buried the head of a pig in the forest behind HCC and covered it in a wire cage to deter large predators. This was the first time they'd been back to check to see what kind of crawling, creeping and flying things had come to feast on the cadaver they affectionately call "Miss Piggy."
As Butin tells students in her "Insects and Forensics" class, different species of insects arrive at a decomposing body at different times. "That's how you can tell how long it's been there," she said.
Entomology, or the study of insects, is critical in forensic science and a principal investigating tool in law enforcement. Since an undergraduate college class can't use a human corpse to study decomposition, a pig head supplied by a local butcher was the next best thing.
"A lot of times pigs are used as opposed to humans because our skin is very similar," says Butin. "The way we decompose is more like a pig than other organism. Most research studies use pigs."
Butin, chair of HCC's Forensic Science program, has conducted this experiment before during past semesters in her "Introduction to Forensics" class. Spring 2013 was the first time she offered a course that focuses entirely on the use of insects in forensics, and she'll teach it again in the fall.
The class meets once a week, in the morning for lecture and in the afternoon for lab. The course covers subjects such as insect morphology, aquatic environments, the ecology of flies and beetles, expert witnesses and DNA.
In the lab, students dissected dead grasshoppers and live cockroaches (to watch their beating hearts).
"When you want to identify an insect," says Butin, "you have to know the parts."
Using dichotomous keys and microscopes, students examined the insects they found on, in and around the pig head and a pork shoulder they also put in the woods.
As the weeks progressed, they collected all sorts of things, such as centipedes and carrion beetles. They brought maggots back to the lab, fed them beef liver and reared flies, because, as students learned, all maggots look alike.
Thus, students were able to distinguish Calliphora Vomitoria, a type of blow fly that regurgitates meat and sucks it up again, from Calliphora Vicina, a blue bottle blow fly, which doesn't.
They looked at cheese skippers, a fly that enjoys organisms in advanced stages of decay -- past the bloat stage, when a dead body expands and fills with gas -- and rove beetles, which eat the maggots and eggs of other insects on a corpse.
In the end, after several weeks of visits, something dragged the pig head off out from under its wire cage. Fortunately, after a search, an intrepid student found it nearby. It was all dried skin and bones.
But that, Butin said, sometimes happens in real life, and in fact, a corpse in that condition attracts a certain kind of skin beetle.
"It's one of the last insects to show up," says Butin. "They will eat hair and bones and really dry skin."
Photos: (Left) Forensics professor Elizabeth Butin holds Miss Piggy before her class buried the pig head in the woods. (Right) Criminal justice major Adam Truong, 29, of Easthampton, looks at a bug collected from the pig head.