Ever wondered what’s inside your favourite bottle of perfume (or after-shave)? How many compounds – fragrance notes – go to make that seductive smell? Turns out that there are lots, maybe 30 or 40 per perfume? It’s all a perfumers (parfumier in French) secret of course; the ‘formula’. But there are thousands of aromatic sources to choose from; natural and synthetic. I came across a website listing some of the formulas!
Well, like many things we humans have made or invented, nature got there first. Orchid bees (euglossine bees) invented perfumes tens of millions of years before humans even evolved!
These little beautiful little Neotropical bees, collect volatile compounds (the building blocks of perfumes) from a diverse range of sources – including flowers, fruits, faeces, resin, sap, decaying wood and even mushrooms – and store them in cuticular pouches on their enlarged hind tibia (below).
Flowers of many different species, including orchids (Orchidaceae), produce scents that specifically attract males of one, or a few, orchid bee species. There are thousands of orchids which are pollinated by both male and female euglossine bees – in countries like Costa Rica Panama and Brazil – whilst they are foraging for nectar, pollen, and resins (Ramírez, 2019). The species specific relationships between the bees and the orchids is another fascinating story, but is also based on unique combinations of floral fragrances. The flowers rely on the bees!
The male orchid bees have special hair-brushes on their front legs with which to mop up the volatile scent compounds. They also secrete large amounts of lipids – from glands in their heads – to act as a carrier for the tiny quantities of perfume (Eltz et al., 2007). The mixture of lipids and fragrances is then transferred to little pouches on their hind-legs: the hind tibial organs. Each orchid bee species – and there are about 250 of them – has their own specific blends, which are then released during courtship displays at mating sites (Pokorny et al., 2017).
Male orchid bees (of the Euglossa species) perform an intricate and repetitive leg crossing movement during hovering flights near the display perch, which has been described as being a bit like them pedalling a bicycle! Males in the genus Eulaema perform wing buzzes when sitting on the perch (Eltz et al., 2005). Anyway, the leg movements transfer the fragrances from the hind tibia to a tuft of hairs on the opposite leg, where they are sprayed into the air via the vibrations of the hind wings (Bembé, 2004). The tibial extracts are described as highly fragrant, and ‘reminiscent of some perfumes’! They are perfumes, but for whom?
It’s tempting to think that the male bees collect and formulate their complex fragrances to attract females, but despite a huge amount of research there is, at present, still no evidence for perfume-based female mate choice in orchid bees (Thomas Eltz, pers. comm.). That does not mean that they are not doing it as a courtship display, just that it has not been definitively proven that females choose whom they want to mate with based on their perfumes.
So why are they doing it?! The fragrances of orchid bees are highly variable and complex, and they go to an enormous amount of trouble – often flying long distances – to collect scents. Some species have over 100 different components in their little leg pouches! (Roubik and Knudsen, 2017). Weber et al. (2016) found an average of 34 +/- 21 compounds per bee. The overall complexity of perfumes, and the number of distinct, or exclusive compounds within a species’ fragrance, was correlated with the number of species in the same genus (congeners) within a given habitat range. So closely related species in the same habitat are accumulating their own unique perfumes. This is how they know who is in their own species, and it stops them mating with a bee of another species. They all must know their own fragrances (and also the smells of other bees in their habitats I guess!). And when different species do evolve, they do so by developing different scents. Flowers like wild arum liliess (Araceae) are highly favoured by orchid bees for their scents (below).
There are thousands of orchids for the bees to choose from (as well as many other sources that smell interesting!).
However, researchers also think that male euglossine bees ‘collect floral and additional fragrances apparently to demonstrate their longevity, skill and species’ (Roubik and Knudsen (2017). The perfumes the male orchid bees make become more complex as they get older. Although different species will have their own innate fragrance preferences, it seems that they also learn from experience. Receptive female orchid bees are probably attracted to males displaying and squirting their perfumes into the air, even though matings are rarely observed (Eltz et al., 2003).
So although a complete understanding of the function of male orchid bee perfumes has yet to be fully elucidated and understood, it is possible that they provide a mechanism for female choice. It is certainly a highly seductive idea. I would love to know how the bee perfumes smell. There are man-made perfumes based on orchids; are there any made to smell like the orchid bee fragrances? Orchid bee essence por homme!
Here is a wonderful video by the late, great photographer Andreas Kay, some of whose wonderful photographs I have used in this blog.
Bembé, B. (2004). Functional morphology in male euglossine bees and their ability to spray fragrances (Hymenoptera, Apidae, Euglossini). Apidologie, 35(3), 283-291.
Eltz, T., Roubik, D. W., & Whitten, M. W. (2003). Fragrances, male display and mating behaviour of Euglossa hemichlora: a flight cage experiment. Physiological Entomology, 28(4), 251-260.
Eltz, T., Sager, A., & Lunau, K. (2005). Juggling with volatiles: exposure of perfumes by displaying male orchid bees. Journal of Comparative Physiology A, 191(7), 575-581.
Eltz, T., Zimmermann, Y., Haftmann, J., Twele, R., Francke, W., Quezada-Euan, J. J. G., & Lunau, K. (2007). Enfleurage, lipid recycling and the origin of perfume collection in orchid bees. Proceedings of the Royal Society B: Biological Sciences, 274(1627), 2843-2848.
Pokorny, T., Vogler, I., Losch, R., Schlütting, P., Juarez, P., Bissantz, N., … & Eltz, T. (2017). Blown by the wind: the ecology of male courtship display behavior in orchid bees. Ecology, 98(4), 1140-1152.
Ramírez, S. (2019). Pollinator specificity and seasonal patterns in the euglossine bee-orchid mutualism at La Gamba Biological Station. Acta ZooBot Austria , 156 , 171-181.
Roubik, D. W., & Knudsen, J. T. (2017). An embellishment that became a mutualism: Inquiries on male bee tibial bouquets and fragrance-producing orchids in Panama and oceanic islands (Apidae: Apinae, Euglossini; Orchidaceae: Epidendroideae). Flora, 232, 117-127.
Weber, M. G., Mitko, L., Eltz, T., & Ramírez, S. R. (2016). Macroevolution of perfume signalling in orchid bees. Ecology Letters, 19(11), 1314-1323.