Dragons that Snap, Oil-drilling Bees

An Academy botanist plays detective to piece together an evolutionary puzzle.

Some flowers secrete oil, rather than sugary nectar, into twin, spur-like extensions of their petals. As hummingbirds have developed different sized nectar-harvesting bills to sip from flower reservoirs of different depths, some bees have evolved long forelegs to gather oils hidden in deep spurs.

Academy botanist Kim Steiner is tracing the origin of this evolutionary oddity by studying two groups of oil-producing flowers and a type of solitary bee in South Africa. Flowers of the genus Diascia in the snapdragon family and a group of oil-secreting orchids (subtribe Coryciinae) are often found in the same habitat and are both pollinated by Rediviva bees. By documenting which bee species visits what flowers, and later comparing this information to the evolutionary history of both types of organisms, Steiner is hoping to solve mysteries such as how oil-secretion developed in these flowers and how easily bees can adapt to reap the benefits of the energy rich oil.

Upper left: Front and rear view of Diascia capensis, an oil-secreting flower with short sacs. It is pollinated by bees with short front legs.
Upper right: Front and rear view of the flower of Diascia tanyceras showing the highly elongated oil secreting spurs. This species is pollinated by Rediviva emdeorum whose forelegs match the length of the
spurs. The yellow spots serve to orient the bee on the flower.
Across bottom: Oil-collecting bees of southern Africa showing the range in body size and foreleg length. Scale line on left is 1 cm.
All photos: Kim Steiner

Studying these ecological relationships requires a lot of time in the field documenting different bees visiting different oil-producing snapdragons and orchids in different locations. Along the way, Steiner has described 13 new species of Diascia and, along with Vincent Whitehead of the South African Museum in Cape Town, has described 13 new species of Rediviva.


Kim Steiner searching for oil-collecting bees near the small town of Clanwilliam in the southwestern Cape of South Africa.
Photo: V. B.Whitehead

Scanning electron micrograph of an oil-collecting bee foreleg. The spathulate hairs are used for scraping the oil while the highly branched hairs hold the oil until it
can be transfered to the hind legs. The round balls in the lower picture are pollen grains.