Achenbach and Foitzik collected 88 colonies of the slave-making P.americanus ant that had abducted workers from three species of Temnothorax. They found that the workers clearly care for the larvae, and nearly all of them were raised until their pupated. But at that point, the slaves' behaviour changed dramatically, taking on a more homicidal bent.If the enslaved Temnothorax are close relatives to nearby Temnothorax colonies that could be targeted by P.americanus, the uprising increases the chances of those colonies surviving. Downloading the full article, we find a few potential strategies for Temnothorax. Escaping and returning home wouldn't work because they're enslaved as larvae, have P.americanus's colony odor and won't be recognized as friendly by Temnothorax on their return. An alternative strategy of going on strike - stopping working - may have negative consequences in forcing P.americanus to conduct new slave raids; the strategy then takes a long time to work. Rebellion is the only useful strategy.
Two-thirds of pupae died before they hatched. The mortality rate was even higher (83%) for pupae containing queens, but very low (3%) for those containing males. The duo saw that the captives were deliberately killing the healthy pupae. In about 30% of cases, as in the photo, the workers would gang up to literally pull the developing ants apart. Another 53% of the pupae were killed by neglect, by workers who moved them out of the nest chamber.
These murders were solely the acts of the slaves. No P.americanus worker ever lifted a mandible against its own pupae. Nor are the deaths a reflection of a generally poor standard of care on the part of Temnothorax. In their own colonies, the majority of pupae hatched, with just 3-10% dying before that happened.
Unresolved questions for me:
- It seems odd to me that other P.americanus wouldn't attack the slaves killing their pupae, but that could be explained by ant defenses being triggered by chemical smells identifying ants as outsiders, and the slaves don't trigger those defenses.
- Why don't Temnothorax destroy all of the P.americanus larvae? They kill the females and workers but leave the males alone. I can buy that there are higher benefits from killing the females and workers, but what's the constraint against which they're optimizing? Are there not enough of them to kill all the larvae in the time available?
Reference: Achenbach, A., & Foitzik, S. (2009). FIRST EVIDENCE FOR SLAVE REBELLION: ENSLAVED ANT WORKERS SYSTEMATICALLY KILL THE BROOD OF THEIR SOCIAL PARASITE Evolution, 63 (4), 1068-1075 DOI: 10.1111/j.1558-5646.2009.00591.x