Gypsy Moths

Homeowners Tactics

Rochester Hills' citizens are the Forestry Division's greatest ally in our efforts to reduce the gypsy moth population in Rochester Hills.  Whether or not an aerial spray to control gypsy moth in a particular year is planned, citizens should be prepared to help do their part to reduce caterpillar numbers in the community.

Gypsy moth egg hatch begins in early to mid May. Citizens should locate and destroy as many egg masses as possible in April. Each egg mass may contain between 50 to 1,500 eggs. Gypsy moth egg masses are fuzzy, tannish brown and irregular in shape, being wider at one end than the other. Generally they are laid against hard objects like tree trunks and limbs, not on the leaves or fine twigs. Often they are found on the underside of tree limbs, under the eaves of houses, under deck railings and play structures. Birdhouses are magnets for female gypsy moths looking to lay eggs.

Once the eggs hatch, the gypsy moth caterpillars can be controlled with applications of the biological insecticide Bacillus thuringiensis (B.t.).  This is a naturally occurring bacteria that is known to affect only young caterpillars that are actively feeding at the time of treatment.  It must be applied to the foliage of the plants they are feeding on.  They must ingest the pesticide for it to work.  B.t. will only control gypsy moth caterpillars while they are still very small.  Once they grow, B.t. will no longer affect them.  As the caterpillars grow larger and more noticeable on the foliage, they begin to make daily migrations down the tree during the day to hide and rest.  This behavior gives the homeowners another opportunity to reduce the gypsy moth population.

Beginning in June, you can place and service burlap hiding squares.  Hiding squares can be made from 18'' X 24'' squares of burlap.  Fold the top half down over the bottom half creating a double flap 18'' X 12''.  Place the burlap at a convenient working height on the trunk of the host tree and staple to the trees bark at the fold.  Lift the flaps one at a time and hold up by using a thumb tack or push pin.  Use a small brush to sweep the caterpillars into a container of soapy water, which kills them quickly (insecticidal soap works best).  The caterpillars should be removed and destroyed daily.  The best time to service the bands is mid-day but late afternoon or early evening may also be effective.

Leaving the burlap in place during caterpillar pupation and the adult egg-laying period (July  August) will often encourage the female to deposit the egg mass behind the squares.  Providing that type of hiding place enables the homeowner to more easily locate and destroy the egg masses.  You can remove the burlap by September.  Don't destroy the egg masses until April to allow egg parasites to complete their life cycles and to allow Forestry staff and volunteers to conduct the annual egg mass survey.

Forestry staff will be available to demonstrate the proper placement and servicing of burlap hiding squares.  The Forestry Division has written information available to citizens detailing how to identify gypsy moth at all stages of their life cycle and effective control strategies that can be implemented throughout the year.