Several different types of worms and caterpillars can infect your aspen trees, but regardless of the type of worm problem you have, the solutions are the same. It is virtually impossible for you to prevent worms and caterpillars from infesting your aspens, but once they have arrived it is possible to get rid of them. It takes persistence and patience, but with the proper tools and rigorous surveillance, you can keep your aspen trees virtually worm-free.
Wrap duct tape around the trunk of your aspen at approximately chest height. Coat the tape with a caterpillar "glue" such as the commercial product Tanglefoot.
Remove any caterpillars that become stuck to your caterpillar trap and drop them into a bucket filled with water and a little dish soap. When the caterpillars have drowned, discard them.
Collect a specimen of the worms infesting your aspens and take the worm to your local nursery for identification. Purchase an insecticide that is specific to that particular worm or caterpillar. Spray your trees with the insecticide on a non-windy day when no rain is forecast for at least 24 hours. (Spray according to the directions on the package.)
Cut a strip of burlap 10 inches wide and long enough to encircle the trunk of your aspen just above the sticky strip caterpillar trap. Tie a string around the burlap band about 6 inches from the top of the band and then let the top 6 inches hang down around the trunk. This will form a place for adult worms and caterpillars to hide.
Check under the burlap strip every day between 4 and 6 p.m. Remove any caterpillars you find using gloves or tweezers, as the hairs on many species of caterpillars can cause rashes. Drop the caterpillars into a bucket of soapy water and allow them to drown.
Use a lawn rake to knock down any visible worms or caterpillars, and any leaves with eggs or any pupa they have spun in order to turn into moths. Pick up all worms and caterpillars, eggs and pupa while wearing gloves (or use tweezers) and dump everything into a bucket of soapy water. Drain the water after the caterpillars have drowned, and discard all caterpillars, worms, eggs and pupa.