You can thank last year's mild winter and a bumper crop of acorns and other nuts for this year's squirrel population explosion.

Greg Yarrow, chairman of the Natural Resources Department at Clemson University, says they're now seeing up to 20 squirrels per acre, when it's normally 5 to 8, "When the numbers become so high they start to seek out maybe some food that they normal would not traditionally eat.  So the damage to fruit producers, nut producers and ornamental planting starts to really increase."

Yarrow says it's had an effect on trees, "From Clemson University's campus we've had over a hundred mature trees that have been killed by the activity of squirrels chewing on the bark and the limbs of trees."

Grey squirrels are the most common, and the most destructive. They're having a devastating impact on the apple crop in parts of New England. Clemson is field-testing non lethal solutions, including capturing squirrels and injecting them with contraceptives.