Crime scene investigators already have plenty to worry about. But now they've got one more foe: squirrels. We're not joking. The rodents with razor-sharp incisors chew up crime scenes to maintain their dentition, says new research led by James Pokines at the Boston University School of Medicine.

The new research, published in the Journal of Forensic Identification, provides clear evidence that squirrels (as well as other rodents) can have a dramatic impact on forensic findings, scattering remains and altering bone fragments to the point where signs of trauma to the bone, such as bullet or knife marks, can be obscured or gnawed away altogether. At times rodent damage can even be mistaken for weapon marks themselves.

The simple study involved wiring whitetail deer bones to hundreds of trees and other locations likely to be favored by squirrels, then returning at regular intervals to record any changes at each sample site. They also used a number of motion-sensitive cameras to catch the crafty critters in the act.

It turns out that bone-gnawing squirrels are pretty pervasive. Of the 305 samples placed, 58 had obvious damage caused by the large rodents; just under 20 percent of the total. Researchers also found that by examining the details of the tooth-marks and other damage, they could determine if it was a squirrel or some other rodent species that had been doing the chewing.

To be fair, squirrels aren't teaming up with criminals on purpose. If you've ever had a pet rodent you know the deal; rodent incisors grow throughout the life of the animal. Unless they are continuously worn down, these teeth can become become so long they can't be used. Unfortunately for forensic technicians, bone on bone is a very efficient method for wild rodents to keep their teeth in chipping condition.

Bone gnawing squirrels also sound creepy. "I was entering our backyard when I saw a very large squirrel holding a vertebra in both hands and gnawing furiously on it," recalls Sierra Santana, co-author and student of Pokines. "We startled each other and I just backed out of the yard to let him do his thing."

In addition to helping people understand the prevalence of this kind of evidence disruption, and helping them distinguish between rodent marks and forensically important marks, Pokines and his team are hoping their work will inspire researchers in other countries to document similar damage by other types of rodents. Meanwhile there's a group of well-read criminals looking for spots with an abundance of squirrels, just in case they need a good location to get rid of the evidence.

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