The female's body is stout and densely covered with hairs, and her antennae appear thread-like. Gypsy moths produce only one generation each year. Vertical objects such as tree trunks where females are most likely to be found attract the males. Females do not fly. Defoliation occurs most frequently in forests on dry ridges and steep slopes that have shallow soils, and on sandy plains that have deep, excessively-drained soils.
Outbreaks also occur frequently along interfaces between forests and urban areas.
Although the natural spread of the gypsy moth has not reached all of the susceptible parts of the United States, the insect has been able to move long distances into new areas as a hitchhiker. Gypsy moth egg masses and other life stages are often moved by cars, recreational vehicles, logs, nursery stock, and outdoor household articles being transported in conjunction with household moves. There are several methods available for monitoring gypsy moth populations. One method involves various techniques for counting egg masses. The third method utilized by NCDA involves the use of special traps baited with a synthetic form of the sex pheromone produced by receptive female gypsy moths to detect the adult male moths.