Pheromone baited traps are the primary method for detecting and delimiting new isolated gypsy moth populations in previously uninfested areas. Pheromone traps are a very sensitive tool that can be used to detect very low density populations that could not be detected using any other method. Field monitoring is conducted by the state and territory agricultural agencies. Primary areas at risk are ships and shipping containers, so the trapping program is centered in the first ports of call for the pest. Traps are cleared fortnightly. Lure replenishment takes place every 6 weeks depending on the longevity of lures in particular climates.

Larvae on foliage are easily distinguishable from other defoliators. Late in the year, host pupae and egg masses on tree trunks indicate gypsy moth infestation. Egg mass counting is a common practice for monitoring infested areas to estimate population density and predict future outbreaks. In North America, the detection of gypsy moth outbreaks is also based on aerial defoliation surveys.

The caterpillar is easily recognizable in the latter part of the larval stage: charcoal grey with a double row of five blue and six red dots on its back. The adult female is approximately 30 mm long, white, with zigzag markings on its wings. The female is incapable of flight and dies about one day after laying its eggs. The male is a brownish colour, much smaller, and survives about one week, mating with several different females.