A Comparison of Two Ants of the Genus Formica

Abstract

This paper is a population study of twc ants of the genus Formica and the species pallidefulva. Ants are often classified intc many subspecies and varieties because differences between closely related groups are sometimes so slight that the taxonomists hesitate to distinguish them as true species. The Formica pallidefulva complex is such a group. Wheeler ('13) lists seven subspecies and varieties of the genus, which range in color from the pale yellow of the typical F. pallidefulva Latreille to the dark brown of F. pallidefulva nitidiventris var. fuscata Emery. I have encountered four of the pallidefulva group while collecting in the North Central states. Of these, F. pallidefulva schanufussi Mayr is the lightest and can live in the most exposed places, such as the poplar dunes of lower Lake Michigan. F. pallidefulva nitidiventris var. fuscata Emery, the darkest of the group, is more likely to be found in shaded woods. The two intermediate forms, which are treated in this paper, F. pallidefulva schaufussi var incerta Emery and F. pallidefulva nitidiventris Emery, are the comman pallidefulvas, being abundant and widespread in woods on sand or clay, in pastures, or along roadsides. These latter two ants are separated in Wheeler's key ('13) by the fact that F. pallidefulva schaufussi incerta workers have a few hairs on gula and petiolar border while F. pallidefulva nitidiventris do not. In general, incerta workers are a little lighter and less shining than are nitidiventris; but individuals vary so much from colony to colony or even within a colony that it is hard to decide whether a certain ant or colony belongs to one group or the other. F. pallidefulva schaufussi incerta and F. pallidefulva nitidiventris were chosen for study with a two-fold purpose: to increase a series of studies in populations of ants such as those carried out for Prenolepis imparis Say (Talbot, '43) and Myrmica schencki ssp. erneryana Forel (Talbot, '45a), and to try to find differences, other than structural ones, which would help to distinguish the two groups of ants. For such a study it was necessary to discover a habitat where both ants nested near each other, where both were subjected to similar changes of temperature, moisture, and light, and where both foraged for the same type of food. Such a location was found at the Michigan Biological Station near Cheboygan, Michigan. Colonies were abundant on the south slope of a sand ridge where aspens (Populus grandidentata Michx. and P. trenuloides Michx.) mixed with red and jack pines (Pinus resinosus Art. and P. banksiana, Lamb), and the ground cover consisted mainly of bracken fern (Pterus aquiline L.) sumac (Rhus glabra borealis Britton), blueberry (Vacciniurn pennsylvanicum Lam.), and reindeer moss (Cladonia rangiferina Web.). Here, during the summer of 1945, nests were dug to reveal their structure; colonies were collected and counted to determine population size and rate of development of brood; and observations were made on flight activities. During July of 1947, another series of colonies were dug in order to increase the number of records. Nest structure.-Emerson ('38), in his study of termite nests, stresses the fact that nest structures are morphological expressions of behavior patterns. With this in mind, similarities and differences in nests of incerta and nitidiventris were noted carefully to see if behavior differences between the two groups could be detected. In general, the nests were quite similar. Both ants are of the type which excavate the soil to form one or more vertical galleries from which radiate the