Gypsy Moth

Gypsy Moth Trapping and Egg Mass Survey

The Wisconsin Gypsy Moth Slow the Spread Program coordinates a statewide trapping survey that provides a picture of where the gypsy moth is located. Trapping is not used as a method of population control. Trapping is a measuring tool.

Seasonal workers place traps at regular intervals in selected counties starting in late May. The trappers then check the traps for catches until the moths stop flying in late summer. Where gypsy moth is present, trapping data can show us the extent of the population. The data also helps the program determine the effectiveness of spray treatments.

In October and November, egg mass surveys are conducted in areas of non-quarantine counties where we find high numbers of trap catches. Egg mass surveys help to identify areas where gypsy moths are reproducing. People in quarantine counties should contact their local suppression program coordinators to report egg masses or any gypsy moth life stage.

Finally, the trapping and egg mass survey data are analyzed to determine which areas in the western half of the state require aerial spray treatments.

How Gypsy Moth Traps Work

Traps do not catch the female gypsy moths because the females do not fly. They release a pheromone (sex attractant) to lure the male gypsy moths to them. This is the key to how the gypsy moth traps work. The cardboard traps contain a strip that mimics the females' pheromone to lure in the males. The insides of the traps are sticky, so once the males are inside the trap, they stay there.

There are two types of traps: the delta trap and the milk carton trap—so named because it is shaped like a milk carton. A delta trap can hold up to 20 moths while the milk carton can hold up to 1,500 moths.

Delta Trap Milk Carton Trap

Trapping Density

The number of traps set within an area depends on where it is located in the state. For instance, in the quarantine counties, where we know we will find gypsy moth, traps are set at one trap per 4 square miles or one trap per 9 square miles. In non-quarantine counties, trap densities are one trap per 1 square mile or one trap per 2 square miles.

Once a trap is placed according to a prescribed grid, the trap location is recorded using a handheld GPS (global positioning system) unit. GPS uses satellites to pinpoint the location of the trap. Throughout the trapping season, trappers then enter the number of moths captured into the GPS units. All the data is then downloaded and sent to program staff for analysis.

Gypsy Moth Trappers

Each year, the Wisconsin Department of Agriculture, Trade and Consumer Protection hires a group of seasonal workers to set traps. A gypsy moth trapper must be able to read maps, enjoy working in the woods, be able to use a GPS unit and be able to keep detailed records. Trappers work for about 12 weeks from late May through September. Every March, a job description and application are posted on the website for downloading.

Egg Mass Surveyors

Once gypsy moth traps come down, a small group of trappers will become egg mass surveyors. They look for egg masses in targeted areas from mid-October to mid-November.

Gypsy Moth Egg Mass

Trapping on Private Property

Trappers and egg mass surveyors are instructed to contact each resident before setting a trap on private property and to ask permission to set the trap. If the resident is unavailable, trappers are to leave an information sheet and a phone number for the homeowner to call for further information. Wisconsin law allows department staff or those authorized by the department to have access to any property to inspect, investigate or control plant pests and diseases. Chapter 94, Wisconsin Statutes.