Orchid Bees (The Euglossines)

By Stephen Buchmann, Pollinator Partnership

Living in the rainforests of the New World are 250 species of the world's most flamboyant bees. The "orchid bees" (the euglossini tribe within the bee family Apidae) are found in forests from Mexico to southeastern Brazil. They are easily distinguished from other bees by their extremely long thin tongues, which can equal twice the length of the body, and their shiny metallic coloration. They also have fewer hairs than most other bees. Orchid bees are living jewels. Most kinds are dark green and shiny with sparse hairs, but they can be brilliant blue, purple, red, gold, brassy, or a mixture of these colors on the head, thorax, and abdomen. The genera within the tribe are Eufriesia, Euglossa, Eulaema, Exaerete, and Aglae, the last two genera are parasitic on other orchid bees. Eulaema are as large as carpenter bees or bumblebee queens, densely black in coloration and densely hairy, but often with wide yellow, orange, or greenish stripes on the abdomen.

Why mention such tropical bees on a website devoted to pollinators within the United States? Orchid bees have recently become a part of our continental American fauna. Along with 22 other species of introduced bees, an orchid bee (Euglossa viridissima) has become naturalized in several areas of Florida where it now routinely visits orchids, other flowers and scent resources. Its population seems stable and expanding into new areas. There is also a record of Eulaema from a single specimen in southern Arizona.

One thing makes euglossine bees unique and different from other pollinating bees. The males interact in highly specialized behaviors with equally complex and bizarre orchid flowers. Certain neotropical orchids (especially the genera Catasetum, Gongora, Stanhopea, and Vanilla) produce strong "medicinal" or flavoring scents that attract orchid bee males to their blossoms from a great distance. Scents including those of eucalyptus, vanilla, and wintergreen are found in the complex scents of euglossine-pollinated orchids. Orchid bee males can be attracted to blotter pads doused with these synthetic orchid scents and this is one way that biologists know about their seasonal abundance patterns and diversity.

Male euglossines visit orchids in addition to tree wounds, fungi and certain flowers to collect scent volatiles. Using specialized scraper hairs on their front legs, they gather up these essential oils and store them within glands in their inflated hind legs. Over a period of weeks or months, males collect a species-specific mixture of scents. One or more males gather in "leks" display sites on tree trunks where they release some of their harvested scents while buzzing, flying out from their tree, and returning. Although rarely observed, females seem to choose among males and mate with them in these territorial sites.

Orchids are unusual flowers. They present their pollen shrink-wrapped in two yellow rounded packets in a precise release and delivery system. In one especially bizarre flower, the bucket orchid (Coryanthes spp.) males are attracted to a scent-producing patch but eventually slip and fall into a water-filled bucket in the lower part of the orchid. To escape, males must crawl through a narrow exit tunnel. They are temporarily held fast by the orchid while the pollinium pollen packets are picked up and then "glued" onto the back of the bee in a species-specific location. Finally, the orchid releases the bee carrying the orchid pollen to travel to a new orchid. There the process is repeated, and if the new orchid is in the female phase, the pollen is pressed into the stigma thus pollinating the orchid. Charles Darwin in his 1862 book "The Various Contrivances by which British and Foreign Orchids are Fertilised by Insects" discussed this and other bizarre pollination relationships, which "trick" bees into visiting and therefore pollinating them.

For Additional Information

• Euglossini, on Wikipedia
• Orchidaceae, on Wikipedia
• Fragrance biology of orchid bees