This paper provides a simple mathematical model of the aggregation behavior of the gregarious intracortical-feeding larvae of the bark beetle, Dendroctonus micans. The model's assumptions are that each individual produces pheromones at a constant rate and reacts positively to a pheromone gradient. These hypotheses have been tested by comparing experiments and simulations, both of which showed that (1) homogeneously distributed individuals aggregate rapidly at the center of the experimental or theoretical arena and (2)