Olfactory eavesdropping is widespread among the social bees, who can use it to avoid predators (Li, J., Wang, Z., Qu, Y., and Nieh J.C. (2014) Giant Asian honey bees use olfactory eavesdropping to detect and avoid ant predators. Animal Behaviour. 97:69-76.) or exploit it to find good food sources.

All social bees have some form of odor marking at the food source, but only the stingless bees use odor trails. There is intriguing variation in the length of these odor trails, with some species producing complete odor trails that extend from the nest to the food source, others producing short odor trails that extend only a few meters away from the food source in the direction of the nest, and finally some that only odor mark the food source alone. Why does this variation exist?

Some stingless bees are highly aggressive (Nieh, Kruizinga et al. 2005; Lichtenberg, Imperatriz-Fonseca et al. 2010) and actively compete with other stingless bees over food sources (Nieh, Contrera et al. 2003). For example, the aggressive species, Trigona spinipes, can evidently eavesdrop and orient towards the odor mark deposited for good food sources by other species such as Melipona rufiventris. In experiments, this eavesdropping occurred when T. spinipes foragers were acting as scouts. Trigona spinipes foragers were also clearly able to distinguish between their own odor marks and those of M. rufiventris. After finding the food source marked by the "victim" species, T. spinipes attacked, drove away, and killed the M. rufiventris foragers, taking over the food (Nieh, Barreto et al. 2004). Recently, we have found that such eavesdropping is strategic and can be applied by aggressive species in a context-dependent manner. Eavesdroppers avoid food sources with higher concentrations of recruitment phermone, perhaps because the cost of fighting over and monopolizing such a resource is too high when it is already being visited by a significant number of competitors (Lichtenberg EM, Hrncir M, Turatti IC, Nieh JC (2011) Olfactory eavesdropping by two competing stingless bee species. Behavioral Ecology and Sociobiology 65:763-774) (Lichtenberg, E., Graff Zivin, J., Hrncir, M. and Nieh, J. C. (2014) Eavesdropping selects for conspicuous signals. Current Biology. 24(1): R598-R599. DOI: http://dx.doi.org/10.1016/j.cub.2014.05.062).

Limiting the conspicuousness of odor marks via strategies such as decreasing odor trail length could be an effective counter strategy to such eavesdropping. However, this would also decrease the amount of guidance information offered to recruits. Providing encoded location information, functionally referential communication, at the nest would replace such lost odor trail information.

Interestingly, all bees for which there is some evidence for functionally referential communication, including honey bees, use only point-source odor marking (Nieh 2004). Whether this is due to eavesdropping and aggressive competition remains to be determined. However, stingless bees and honey bees still aggressively compete in the environments and regions in which they evolved. Thus, we speculate that eavesdropping may have contributed to the evolution of functionally referential communication at the nest.

In the video below, Trigona hyalinata (an aggressive Brazilian species of stingless bee) is shown here attacking, pinning, and ejecting a much larger stingless bee from a rich sucrose feeder. This video was shot by Shawn Kessler at the Fazenda Aretuzina, Brazil.

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