High densities and brood rearing in the antMyrmica rubra L.

Abstract

1. Interaction of increasing forager numbers with nurses in a limited living space gave numbers and weight increases comparable to low density cultures in plane nests. The foraging population included a small but constant number of nurses. 2. Eight living volumes, length 1–8 cm (6 mm diam.) gave no increase of mean foraging population in the 2nd of 2 three-week periods of counting. No noticeable difference, between treatments, or from day to day was shown. An indication of density effect was shown by the two smallest cultures, otherwise the mean brood weight regressing with inside worker number supported a lack of density effect. 3. Eight living volumes, length 0.5–4 cm (4 mm diam.) gave no rapid brood but residual larval numbers regressed with relative available living space. 4. A repeat trial, 0.5–4 cm (4 mm diam.) suggested a change of worker packing with a constant number of residual larvae except in the two smallest cultures. 5. Change of packing was not successfully observed as workers maintained a tight packing pattern throughout, corresponding however to the tightly packed stage of the previous experiment. A constant fall of insiders, 10 workers/cm length was observed. 6. Brood loss in high density cultures seems likely to be caused by worker aggression. Two chewed-up larvae were observed. 7. Interaction of queen effect and high density, caused least weight gain for large, hibernated larvae although high density alone had considerable inhibitory effects. 8. Queen presence and high density had a lesser but definite effect on small hibernated larvae. Losses were greater and weight gains smaller when a queen was present at high density. She has a physical volume equivalent to 3 workers and a «behavioural» presence of the same number and these latter were excluded when space was limited.