BIOTIC ASSOCIATIONS OF COCKROACPIES— ROTII & WILLIS 323 



reported that cannibalism was common in a laboratory colony of Peri- 

 planeta hrimnea and that egg capsules deposited by a female were 

 often eaten by the other cockroaches. 



Periplaneta americana occasionally ate other cockroaches and their 

 oothecae and also attacked members of their own species (Lederer, 

 1952). Griffiths and Tauber (1942) recorded the killing of male 

 American cockroaches by females of the species : "One female was 

 especially vicious and attacked each new male as he was introduced 

 into the container. Jvlost of such males had molted less than 2 days 

 previously. Older males were more capable of defending themselves 

 against attacks of these cannibalistic females." Even though adequate 

 food may be present, females of Periplaneta americana may eat their 

 own eggs (Klein, 1933). Some females may regularly eat their oo- 

 thecae as soon as they are dropped (Griffiths and Tauber, 1942). To 

 be completely eaten an ootheca generally must be attacked before it 

 has hardened. If a hole is eaten in one side of the capsule, the cock- 

 roach may devour the eggs and leave a portion of the ootheca. Fre- 

 quently only the keel or a part of the keel is eaten and when this occurs 

 the eggs fail to hatch and usually do not complete development because 

 of the rapid loss of water (Roth and WilHs, 1955). When adults of 

 P. americana and P. aiistralasiae were deprived of food, both males 

 and females ate newly deposited eggs and, finally, the females ate the 

 males (Sonan, 1924). 



Parcohlatta virginica in laboratory cultures also may eat part of its 

 oothecae ; in this species only the soft end of the recently deposited 

 ootheca was eaten (Roth, unpublished data, 1957)- 



Cros (1942) observed oothecae-bearing females of Blatta orientalis 

 attack and kill males of the same species which were attempting to 

 mate ; these males were then eaten by the females. Cros also observed 

 injured and recently molted nymphs of B. orientalis to be eaten by 

 others of the same species. 



Pettit (1940) noted that cannibalism in his culture of Blattclla 

 germanica occurred only when the insects were molting. Adult insects 

 attacked the molting cockroaches more often than did the nymphs. 

 However, nymphs after the fourth instar occasionally set upon other 

 molting nymphs. First- to third-instar nymphs rarely victimized their 

 mates. The victims were all older than third instar ; the later stadia 

 were progressively more subject to attack, and molting adults suffered 

 the greatest mortality. No direct correlation was noted between popu- 

 lation density and cannibalism. 



