Sub-social behavior in a burrowing cricket Anurogryllus muticus (De Geer)

Abstract

Sub-social behavior, or specialized parent-offspring interaction that terminates before the offspring mature, has been noticed in a wide variety of arthropods: millipedes, centipedes, scorpions, pseudo-scorpions, crustaceans, spiders, mites, web-spinners, cockroaches, earwigs, treehoppers, shield-backed bugs, giant water bugs, beetles, wasps, and bees. Except for wasps and bees, it has been described in detail in only a very few cases, perhaps most notably the earwig, Forficula auricularia L. (Fulton, 1924; Weyrauch, 1929). This is surprising in view of the extent of investigations on the truly social insects (ants, wasps, bees, and termites) and of efforts to reconstruct the sequences of change by which they have evolved their distinctive characteristics: division of labor, sterile castes, and complex communication (Wheeler, 1923; Michener, 1953, 1958; Evans, 1958). Various authors have mentioned that some female mole crickets (Gryllotalpinae) isolate themselves in their burrows with the eggs, live beyond the hatching of the eggs, and display hyper-aggressiveness in this situation (Hayslip, 1943; Hahn, 1958). Females of Brachytrupes achatinus Stoll (Brachytrupinae), the big brown of India, deposit their eggs shallowly in the end of one of their galleries and the young nymphs leave the parental burrow a few days after hatching (Ghosh, 1912). Liebermann (1955) noted that the female short-tailed cricket, Anurogryllus muticus (De Geer) (Brachytrupinae), lives in the brood chamber until the second or third molt of her offspring. This paper reports some details of parent-offspring interactions in the short-tailed cricket, discusses their adaptive significance, and hypothesizes that certain morphological and behavioral characteristics of non-social and sub-social crickets pre-adapt for the evolution of greater complexity in parent-offspring interactions. We have raised five families of Anurogryllus to partial maturity in the laboratory, and in one case were able to watch and photograph during a period of several weeks the behavior of a female in a burrow which she had excavated in sand along the glass wall of a jar (fig. 1-6). This female was collected as a juvenile in Kannopolis, North Carolina, on May 25, 1961; she mated in early June when a male was first placed in her cage. Single matings per female are not otherwise known in crickets, but after mating once, this female showed only aggressive behavior toward males that were placed in her cage and then watched continually while they courted her for long periods, both inside and outside burrows. During the weeks following her mating, the female excavated an underground chamber into which she carried particles of apple, peach, and grass supplied in the cage, and from which she ousted intruding males and females alike. In expelling one male which we had purposely introduced into her burrow she actually tore off one of his hind legs (fig. 2); after repairing the damage to the burrow entrance, she ate the severed leg (fig. 3). Although we have watched several thousand cricket fights involving approximately 30 species in four subfamilies and ten genera, this is our only record of definite physical damage; and it is apparently the only clear record of cannibalism as a result of cricket aggression. Both facts are surprising, for the males of this species are the most successfully territorial and the least violent of burrowing crickets in their aggression (Alexander, 1961); additionally, in this case the male did not at all reciprocate the female's aggression. Aside from this species, intense aggression among crickets is known to occur only in males, and only when both individuals are hyper-aggressive.