Dead pigs do, as a matter of fact, tell tales

DNA analyst, others learn lessons on decay from insects, animals

Wednesday, Oct. 27, 2010

Click here to enlarge this photo
Staff photo by DARWIN WEIGEL
J. Thomas McClintock of Owings is a forensic DNA analyst with DNA Diagnostics Inc.

In September, two corpses lay side by side in the woods in Owings: an adult and an infant. Fortunately, this was not a real crime scene, only a science experiment, and the victims were pigs, not people. The scene was gruesome nonetheless, with the bodies decaying into skeletons over the course of about 12 days.

But the exercise served the dual purpose of giving forensics graduate students a realistic experience and providing data about the deterioration of corpses in Southern Maryland, said J. Thomas McClintock, an adjunct professor at George Mason University who teaches DNA analysis and forensic entomology courses in its new forensic science program. McClintock, an Owings resident, also owns DNA Diagnostics, a company that does forensic and paternity genetic testing.

While DNA is the professor's specialty, the purpose of this exercise was to catalogue the insects that infested the exposed corpses. The information would let entomologists, those who study insects, deduce the approximate time a crime victim had died based on the species and developmental stages of the bugs infesting the body, McClintock explained.

The dead animals were surrounded by wire mesh to keep scavengers away. Containers full of antifreeze were set into the ground around the corpses to capture and preserve examples of insects that showed up to feast.

Pigs are the next best thing to a human corpse, McClintock said, because our tissues are similar to theirs. The problem was getting fresh specimens.

"That was quite a feat, trying to find a live pig. I started with the Bowen's [Grocery]. I didn't want it cleaned. It needed to have all the entrails," he explained. Eventually he found an Amish farmer in Mechanicsville willing to oblige him. The man dispatched the animals, which McClintock dubbed Stewart and Scrappy, with a .22-caliber rifle while the scientist waited. The farmer, used to producing food, felt guilty about charging him money for meat that no one would eat, McClintock said.

Or ever want to eat. Blowflies arrived immediately to lay eggs in the fresh corpses, already infesting Stewart before McClintock could unload Scrappy from the car. It wasn't long before maggots were squirming in the flesh, and in about a week and a half the corpses were all but gone.

Aspects of the experiment gave laymen pause.

Scrappy was just a piglet, so McClintock dressed him in baby clothes to see if clothing would have any effect on the rate of decomposition. (It didn't.)

"My wife was like, ‘That's a little different. Don't you feel a little strange about that?' I was like, ‘I'm trying to answer a scientific question,'" he said.

Puna Miller of Dunkirk, a friend and freelance photographer McClintock enlisted to document the decomposition, also was taken aback by the baby pig, although she'd been warned.

"He's a scientist, passionate about that type of thing, but I'm an artist, a mom, and it was something that — once I got started, actually, the first session was not so bad. The pigs there were freshly killed. One had clothes on, the little one had on a little ‘onesie' thing, a little disturbing, ugh," Miller said.

The assignment was "a good experience," but she wouldn't take a similar one again, Miller said.

A similar conclusion was reached by the three students who accompanied McClintock to the site in the woods behind his home to collect the insects, all of whom said they were grateful for the experience but probably would not pursue forensic entomology as a career.

As a new forensics student, graduate student Andrew Roller of Falls Church, Va., said he was probably less prepared than the other two, who study biology, for what they would encounter during the visit.

"I'm very new to it, so I don't know if I can say I'm used to it yet, but I'm prepared for it. … The smell was pretty intense," Roller said, especially when emptying the traps containing preserved insects. When collecting samples from the "larval mass" in each pig, a clump of maggots that roves through the corpse in search of food, he was afraid he would fall into the rotting flesh, he said.

But even without specializing in insects, Roller said what he learned will be valuable.

"It's the type of thing I think a Ph.D. in biology would be more likely to go into, but the information is definitely very useful. As a crime scene investigator, knowing generally what the insects are, if there's clearly third-instars [late-stage larvae] on the corpse and what that means … it can make a big difference in what you're looking for and make the process go a lot faster," he said.

Once the specimens were collected and preserved, it was the job of the entire class to figure out the species of the beetles, flies and larvae, and what their presence meant about the circumstances of the deaths.

"We've only identified two or three species so far. Hopefully by [the] end of the class we'll be experienced and able to pinpoint exact[ly] what we have and from that determine how long [ago] he had put the pigs there," said graduate student Zachary Combs of Richmond. "… Absolutely, the minute variations are really difficult, especially with the immature larvae." Larvae have to be identified by the shape of their mouth hooks and by the number and pattern of tiny slits on their rear, McClintock said.

McClintock started paying attention to insects in an agricultural context. He was looking for viruses that would infect the larvae of pests that prey on crops. Despite his persistent interest in insects, he said he's glad it's not his only focus. "I don't think it's something I'd want to spend 40 hours a week doing," he admitted. In addition to marking time, maggots who have fed on a human cadaver can be used to obtain samples of the victim's DNA and learn whether the victim had drugs in his system when he or she died, McClintock said.

"I think it is really kind of amazing that you can do that through the use of insects, identify human, identify the time of death and identify the illegal substances used by [the] host the insects have been feeding on. These silent witnesses can tell you, if you just ask them," he said.