[Aggregation behavior of Blattela germanica]

1. The adult males of the German cockroach Blattella germanica are less strongly aggregated in their resting period than the adult females; they seldom stay below the common hiding place. This tendency decreases in the course of a day.--2. The nymphs aggregate in the first days of their lives below the hiding places of the adults where they had left the oöthecae. Later the nymphs seek hiding places that are better adapted to their body size. An olfactory stimulus (aggregation pheromone) which is going out from the adult induces the nymphs to go back again to the adults in the course of a day. This tendency decreases more when the nymphs become older. At the same time the number of nymphs which are absent from hiding places increases.--3. A positive chemotactic and a positive thigmotactic reaction are responsible for this behaviour of the cockroaches. A phototactic negative reaction is less important.