Creature Feature: Orchid Bee

“A powerful and captivating scent, Oud is combined with Patchouli and notes of Saffron for an intense, woody fragrance that captures the mysterious and hypnotizing nature of the snake.” Thus waxes Gucci about its Nature of the Snake cologne for men. If Gucci were to create a Nature of the Orchid Bee cologne, it might read more like “a delicate swirl of vanilla and cinnamon combines with powerful overtones of eucalyptus and a dollop of rotting meat to form this potent odor that is sure to entice all potential suitors.” Fortunately, Gucci doesn’t have to make this perfume because male orchid bees do it themselves!

The metallic green coloration of this orchid bee pair is the most common coloration seen among over 250 species. [Source]

If you don’t know of the orchid bees, they are a tribe (Euglossini) of over 250 species and counting! In addition to the intricate perfume-mixing behavior of the males, which I will get back to shortly, orchid bees are known for their colorful, iridescent bodies. Most are a metallic green, but others are purple, red, orange, blue or some combination of these colors. As vivid as they are, orchid bees can be difficult to spot in the wild; they are only found in the Americas, where they are typically zooming around in dense tropical forests. The best way to find orchid bees is to follow your nose; the fragrance of a wounded tree will draw males by the dozens.

Orchid bees vary in color, like this shiny blue specimen (Exaerete frontalis) collected in Mexico. [Photo taken by: Alejandro Santillana, Source]

It is not just tree wounds from which orchid bees collect scents; pretty much any powerful smell will draw them in. In fact, their common name is inspired by the more than 700 species of orchid flowers that rely exclusively on orchid bees for pollination. These flowers don’t produce nectar, but instead emit perfumes which attract one or more species of orchid bee. When the bees come to the flowers to collect these scents, they often get trapped in a tube inside the flower which has a spring-loaded pollen sac ready to be glued onto the backs of the scent-hungry pollinators! The process of scent collection itself is pretty involved; I’ll leave it to the experts to explain:

“First, the bee lands on the fragrant surface and applies to it droplets of lipids secreted by its labial glands in which the nonpolar volatiles [(scent chemicals)] are dissolved and retained, analogous to the greasy extraction (‘enfleurage’) used in the perfume industry. Then the bee uses setal brushes on its fore-tarsi to absorb the mixture, hovers up, and quickly transfers the liquid to the hind tibiae by squeezing the fore-tarsal brushes through specialized combs on the mid basitarsi. Once deposited on a hair-filled groove on the hind tibiae, the liquid is drawn inside the cuticular pouches by what seem to be capillary forces.”

(Eltz, Sager, & Lunau, 2005)
Footage from the Smithsonian Tropical Research Institute (STRI) captures orchid bee scent collection in action. [Source: Smithsonian Channel]

Each species of orchid bee blends its own specific mixture of volatile compounds [2]. And even though each species has its signature perfume, individuals within a species also vary in their mixing methods. Older bees tend to have the strongest, most complex perfumes and compositions vary by region and season. Interestingly, however, perfume composition does not vary as much as one would expect based on differences in scent availability. Orchid bees use negative reinforcement learning to adjust their collection habits, meaning that as they encounter more of a certain scent they learn to avoid it and seek out rarer scents instead [3].

The enlarged hind leg of orchid bees contains a sweat gland for storing scents. The orchid bee picture above (Exaerete frontalis) was collected in Mexico [Photo taken by: Alejandro Santillana, Source]

So why go to all the trouble of painstakingly collecting and blending smells? Most experts agree it is probably to attract mates, but observing that directly has proved very challenging. What we do know is that the specific smell combinations of species that either live in the same area or are closely related to each other tend to be the most different [2]. This is evidence that perfumes are used for species-specific identification. Males also spray their fragrances in display territories that they aggressively defend [4]. It appears that by creating the correct mixture, the males advertise to females that they are a species-appropriate mate. I, for one, will henceforth refer to anybody with too strong a perfume or cologne as an orchid bee and let them wonder what that means.


Alexander Vining is a fourth year Ph.D. Candidate in the Animal Behavior Graduate Group. In affiliation with the Smithsonian Tropical Research Institute, he studies the spatial memory and movement of frugivorous mammals (including the kinkajou) on Barro Colorado Island, Panama. Alexander has a particular love for the elusive animals of the canopy, and enjoys any research that brings him into the tree-tops.


References:

  1. Eltz, T., Sager, A., & Lunau, K. (2005). Juggling with volatiles: Exposure of perfumes by displaying male orchid bees. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, 191(7), 575–581. https://doi.org/10.1007/s00359-005-0603-2
  2. Zimmermann, Y., Ramirez, S. R., & Eltz, T. (2009). Chemical niche differentiation among sympatric species of orchid bees. Ecology, 90(11), 2994–3008. https://doi.org/10.1890/08-1858.1
  3. Pokorny, T., Hannibal, M., Quezada-Euan, J. J. G., Hedenström, E., Sjöberg, N., Bång, J., & Eltz, T. (2013). Acquisition of species-specific perfume blends: Influence of habitat-dependent compound availability on odour choices of male orchid bees (Euglossa spp.). Oecologia, 172(2), 417–425. https://doi.org/10.1007/s00442-013-2620-0
  4. 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. https://doi.org/10.1111/j.1365-3032.2003.00340.x

Main featured image: “An orchid bee euglossa viridissima hovering near a Fire Bush flower.”[Source]

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