The Sexual Ruse of the Bee Orchids

There are flowers out there that offer rewards far more enticing than any amount of pollen or nectar - they offer sex. Sexual deception is a rather tricky way of achieving pollination. By duping sex-crazed male insects into thinking they have found a female rather than a flower, such plants have tapped into an irresistible force of nature. Nowhere is this more beautifully illustrated than the orchids belonging to the genus Ophrys

Collectively referred to as the bee orchids, Ophrys grow native throughout much of Europe, North Africa, the Canary Islands, and parts of the Middle East. Phylogenetically speaking, they are a bit of a mess. Estimates of the number of species range from as few as 20 to as many as 130. The range of variation in floral color is staggering and has everything to do with the evolution of this genus. 

The reason they are called bee orchids is because that is exactly what they have entered into an evolutionary syndrome with. And what an evolutionary relationship it is! The bee orchids have evolved to trick male bees into thinking their flowers are receptive females. 

The most obvious aspect of this ruse is their appearance. Though there is quite a lot of variation, the overall theme is that the labellum acts as a female dummy complete with hairy abdomens and, in some species, iridescent wing marks. The ruse does not end there. Far more convincing than their appearance is the odor released by each flower. 

Ophrys produce chemical compounds called "allomones." These allomones closely mimic the pheromones released by female bees. What's more, each species of bee orchid produces allomones specific to the species of bee they are trying to attract. For some this can be very specific, attracting males of only a single species. For others it would seem that a small handful of different species have fallen for the orchid's trick. 

Regardless, male bees find these flowers irresistible at first, often preferring flowers to actual females. However, the males soon learn to avoid flowers, which results in consistently low pollination rates. This doesn't seem to be much of an issue for these orchids as a single plant can produce tens of thousands of seeds. 

This pollination syndrome has obviously worked for this genus. Slight mutations on the allomones produced have led to the massive radiation of Ophrys species we see today. Even more amazing is that research suggests that most of this radiation has occurred since the Pleistocene. 

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Further Reading: [1] [2] [3] [4]