Patterns of subadult gypsy moth,Porthetria dispar(L.), occurrence within a sparse, numerically stable population that was studied in 1965 were modelled as functions of insect stage and certain components of environmental structure. Our results imply the following. (1) Once newly hatched larvae find suitable foliage, they tend to stay on or near it until after they have molted into instar III. (2) These insects begin to wander sometime before reaching instar IV, and continue to do so until suitable daytime resting locations are found. These locations are usually in the litter at the tree base, but the insects will aggregate under bark flaps on dead limbs or on the dead boles of trees in clumps in preference to the litter if these are available. (3) Most of the insects pupate in the locations used earlier for resting sites, but some eventually pupate in objects that may be many feet away from the closest living host tree. (4) Bark flaps may have provided less hazardous resting sites for the growing larvae and pupae than other potential resting locations within the environment.