Speed-accuracy trade-off in egg recognition underlies seasonal acceptance of parasitic egg-mimicking fungi in termite colonies.

Social insect colonies rely on accurate brood recognition to maintain colony integrity and reproductive success. In termites, however, this recognition system is exploited by egg-mimicking fungal sclerotia known as “termite balls,” which are transported and tended by workers. Yet the mechanisms underlying these recognition errors are not well understood. Here we show that egg recognition in Reticulitermes speratus involves a speed–accuracy trade-off, where faster egg-pile formation leads to more frequent acceptance of mimics, and that this trade-off is seasonally modulated, potentially generating a predictable window for social parasitism during peak reproductive periods. In the season when eggs were present, workers formed egg piles more quickly and transported dummy eggs (glass beads coated with egg-recognition pheromone) more readily than when eggs were absent. Importantly, even in off-season colonies lacking eggs, repeated transport trials, using eggs supplied from laboratory-maintained colonies, sensitized workers to transport both eggs and mimics. Across trials, we observed a speed–accuracy trade-off: faster pile formation was associated with a higher proportion of mimics mistakenly included in the egg pile. This behavioral plasticity, while adaptive for efficient brood care during peak reproductive seasons, inadvertently increases susceptibility to parasitic infiltration. The egg-mimicking fungus Athelia termitophila is consistent with this mechanism, as its termite-ball sclerotia are treated as eggs by workers. Our results show that seasonal changes in colony workload modulate the balance between speed and accuracy in brood recognition, revealing a behavioral mechanism through which predictable vulnerabilities can arise in social insect colonies.