Question
We have a chinese (japanese ??) elm in our back yard and squirrels have been biting off the ends of limbs for about two weeks. It makes a mess on the ground that has to be raked up and disposed of. Can you explain why they are doing this? Thank you

Answer
Sounds like an insect called a twig girdler or twig pruner.

Small branches accumulating on the ground and the presence of clean-cut twigs, and in some cases dangling (flagged) branch tips within a tree, indicate the presence of beetle pests referred to as twig girdlers and twig pruners. Both of these long-horned beetle species (Cerambycidae) attack numerous types of shade, nut and fruit trees. Heavily damaged trees appear ragged and unattractive, and young trees can become deformed by repeated attacks.

Common hosts of the twig girdler include persimmon, pecan, elm, hickory, oak, honeylocust, hackberry, poplar, linden, redbud, basswood, dogwood and various fruit trees.

These insect lay there eggs in the bark of a twig and then cut the twig below the egg laying site. The twig falls to the ground where the insect will mature. The eggs hatch and the larvae feed in the twig until mature.

Adult female twig girdler chews a V-shaped groove from the outside inward, leaving a ragged center where the twig breaks and a smooth cut on the outside near the bark.

The twig pruner chew through the wood from the inside outward, leaving a smooth cut on the inside of the twig with ragged edges near the bark where the twig breaks.

It really does not mater which beetle it is since the controls are the same. During the fall or winter, gather fallen branches from the ground and prune suspected infested branches still in the tree and burn them. This will destroy the population and greatly reduce or eliminate any damage the next year. The tree is not really damaged by these insect unless the cutting is severe and over several years.


Here is a web link to more information on twig girdlers.
http://www.ag.auburn.edu/enpl/bulletins/twiggirdler/twiggirdler.htm