W. L. Brown, Jr.
A Formica Slave-maker Raiding the Nest of a Myrmicine Ant.
Psyche 65(1):39-40, 1958.

This article at Hindawi Publishing: https://doi.org/10.1155/1958/10296
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A FORMICA SLAVE-MAKER RAIDING THE NEST
OF A MYR'MICINE ANT
Museum of Comparative Zoology
Slave-making Formica of the sanguinea group normally raid the nests of Formica of the fusca, pallidefulva or neogagates groups to obtain pupae to be reared into slavery. Occasionally, F. sanguinea group species have been seen to raid other formicine genera, especially Lasius, and Wheeler (1905, Bull. Amer. Mus. Nat. Hist. 21: 11) even recorded a raid on a nest of Myrmica (subfamily Myrmi- cinae) species that he watched in Connecticut. Raids by Formica on myrmicines apparently are rare occurrences, so the circumstances of such a raid are worth reporting. On August 22, 1958, at Brown County State Park, In- diana, I witnessed a raid by Formica subintegra Emery on a nest of the much smaller myrm'icine ant Aphaenogaster rudis Emery. The nest entrances of the raiders and the victims were simple holes situated only about one meter apart in the bare clay soil of a hilltop campground, shaded by hickories and a few oaks. The raid was first noticed at about 3 P. M., about 3 hours after a heavy rain had ceased. The sky was partly cloudy, and the air temperature stood at about 70å¡F
Most of the visible activity occurred in and around the entrance to the A. rudis nest. Six dead or badly maimed rudis workers lay near the entrance, accompanied by one crippled F. subintegra worker. One subintegra worker grappled with a rudis worker and put it out of action while I watched. At irregular intervals, subintegra workers em- erged, most of them carrying a pupa or a dead or struggling worker of A. rudis, with which they returned directly to their own nest and entered there. Two subintegra workers carried folded-up workers of their own species ; when dis- turbed, these workrs dropped their burdens, which proved to be active and apparently unhurt.




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40 Psyche LMarch
Around their nest entrance, at some distance, circled a few Aphaenogaster workers, mostly each carrying one of their own larvae or pupae. Their behavior resembled that of Formica slave species when being raided by F. subintegra. Also running in the general vicinity of both nests, but not seen to participate directly in the raid, were a few workers of Formica fusca (s. lat.), all of them slave mem- bers of the F. subintegra colony.
The raid was under observation for about one hour, and my impression was that it had been in progress for %ome time before I first saw it. It compared with the terminal stages of other raids I have seen F. subintegra make on other Formica species. The raid was terminated by heavy rain in the early evening, and was not continued on the next day.
On partial excavation, pupae and dead or injured workers of A. rudis were found in the subintegra nest, but there were no Aphaenogaster workers present and intact that seemed to be acting as slaves. Therefore, I concluded that the raid would probably not be successful in introducing the Aphaenogaster into adult slavery.
In the present observation, it is not known whether the captured pupae or adult Aphaenogaster workers were eaten by the Formica raiders. But even if they were, such behavior is not necessarily of more than routine significance, since ants will eat their own pupae under various circumstances. My own interpretation of the raid is based on the apparent lack of nests of suitable slave species of Formica in the campground, and the abnormally exposed nature of the Aphaenogaster nest. Since F. subintegra workers had been seen foraging singly over the area for several days previous to the raid described, I suspect that these represented scouts- that were unsuccessful in locating suitable Formica sup. nests to plunder. Under such conditions, the pressure for the release of raiding activity may have been high, so that eventually even such a poor target as the Aphaenogaster nest came to represent a stimulus sufficient to start and maintain a raid.




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