Lanchester’s models of combat have been invoked to explain the mechanics of group fighting in social animals. Specifically, Lanchester’s square law posits that the fighting ability of the group is proportional to the square of the number of combatants. Although used to explain a variety of ecological phenomena, the models have not been thoroughly tested. We tested the Lanchester models using group battles between colonies of the termite Nasutitermes corniger. Our main goals were to determine if mortality rates fit the Lanchester models, and if so, whether the behavioural mechanisms underlying a group’s success match those used in deriving the model. We initiated battles between pairs of colonies with different ratios of fighters and recorded deaths over time. We found that the numerically larger army has an advantage, but that the advantage is not as pronounced as predicted by Lanchester’s square law. We also video-recorded battles to analyse individual behaviour, which did not support the mechanisms invoked by Lanchester. Instead, the killing power of an individual is increased by the presence of nestmates, giving the larger group a disproportionate advantage. Although the behavioural mechanisms leading to the advantage may differ, our results still support some of the proposed ecological phenomena.

Intraspecific battles were performed using the termite Nasutitermes corniger. N. corniger is abundant at the La Selva field station in Costa Rica, which is situated in a lowland tropical rainforest (10.430623, -84.006971). This species builds arboreal nests that can house thousands to millions of termites that are highly territorial (Adams & Levings, 1987; Thorne, 1980; Thorne & Haverty, 1980). Consequently, intraspecific battles between colonies can be observed naturally in open air (Levings & Adams, 1984). Termites from two castes were collected: workers and soldiers. The soldiers shoot a gummy-like substance from their cone-shaped heads, which is more effective against ant and vertebrate predators than other termites (Thorne, 1982). Thus, we focused on workers, which use their mandibles as both a defensive and offensive weapon.

For trials, workers were picked arbitrarily and their abdomens were painted using Testors paint to identify their colony (N=6) of origin. Initial ratios of 40:10, 25:25, and 10:40 workers were used for each colony pairing and each ratio was replicated three times per colony pair. Each colony was only paired with one other, resulting in 27 battles. Battles were staged in 60 x 15 mm petri dishes. As a control, fifty painted and fifty unpainted workers from each colony were placed in separate petri dishes for 12 hours, with deaths counted every hour (deaths ranged from 0 to 2 total).