The Stable Winter Population Structure in Species of Myrmica

Abstract

Colonies of Myrmica laevinodis and M. rubra have a characteristic composition in winter. In an observation colony of laevinodis in normal climatic but ample trophic conditions the ratio of workers to larvae was very constant for 3 successive winters (by number and weight). Analysis of rubra colonies collected from the field in winter gave a good linear regression of larval wt. on worker wt., passing through the origin (proportionality). The relation between the numbers of larvae and workers was either subject to more variation (assuming linearity of regression) or failed to achieve linear expectation in large colonies (curvilinear regression). The consequences of this under-production in large colonies, since the avg. wt. was approx. proportional to the worker/ larva ratio (numbers), was a higher avg. wt. of larvae. The dominating weight relationship implies competition between larvae in their "trophic field," and the results are similar to those usually associated with such in other insects although these do their own foraging and mastication.