INTRASPECIES FIGHTING
Fighting occurs among cockroaches of the same species over food or shelter or between males. Saupe (1928) observed late-instar nymphs of Blaberus craniifer attack each other and even adults. Additional records cited in the section on intraspecies predation (p. [322]) imply fighting within a species. Rau (1924) saw a male of Blatta orientalis attack another male in copula and bite away a large portion of its wing. Two other males in the container had their wings badly torn overnight, presumably as a result of fighting.
Ehrlich (1943) stated that individuals of Periplaneta americana that are feeding will ward off intruders by spreading their wings and pushing with their hind legs. However, the intruder will approach again and again biting the feeder in the legs and wings. Frequently the odor of approaching food was sufficient to cause the cockroaches to fight and bite each other. Biting and fighting also occurred when individuals of this species defended their daytime hiding places. A position of attack is assumed when two antagonistic individuals of P. americana meet (Ehrlich, 1943, fig. 14). The insects raise their bodies slightly above the ground, by extending their legs, and they stretch their heads forward horizontally so that their mouth parts protrude; when the insects jump at each other, they may wound each other severely in the soft parts of the body. Fighting between sexually excited males resulted in injury to their legs, wings, cerci, and other parts of the body. Frequently an insect that could no longer defend itself was killed. Lederer (1952) also made similar but less extensive observations on fighting in this species.
Pettit (1940) quoted Woodruff as stating that nymphs of Blattella germanica, apparently healthy and perfectly normal, would do battle for no apparent cause other than a chance meeting, and that occasionally the fight was to the finish, the loser being eaten. Pettit could not substantiate such voracious attacks, although he saw nymphs engage in fights lasting about two seconds during which one would be driven off by vigorous bites on legs or cerci. Small nymphs of B. germanica tended to ignore each other, but third-and later-instar nymphs would engage in "quarrels" of short duration when two met. Pettit noted that males of B. germanica that were crowded together quickly set upon, but did not always kill, other cockroaches introduced into their cage. When he isolated a dozen males in a small cage, they became quarrelsome and three of the group were killed and partly eaten. After several days the surviving males had taken positions so that each was equidistant from his neighbors. Some of these males attacked other males and a female that were introduced, by biting their legs and cerci. Females under similar conditions were much less aggressive, although Pettit saw some females that roved about biting all large members of the group that were within easy reach.
We have frequently observed aggressive behavior between males of Nauphoeta cinerea, which resulted in torn wings. The males would wrestle with each other rolling over and over.