Let’s suppose you’re shopping for hot sauce. You probably have a favorite brand. You may be very firm about it. Let’s say you’d definitely buy Tabasco, but you’d rarely buy any other brand. To the manufacturer of Tabasco, you’re a more valuable customer because you stick to that brand. Now let’s say you’re a bee. You could sip nectar and eat pollen from any flower you find, or you could have “brand loyalty.” Let’s say you always do your dining at prairie clover, as long as it’s available. From a plant’s point of view, you’re a valued customer if you most often dine at the same species, because you’re more likely to spread that species’ pollen to other flowers of the same species, where it can pollinate those flowers’ seeds.
Certain bee species do have brand loyalty, particularly when it comes to pollen. It’s more than just a bee figuring out the most efficient way to get food from a particular size and shape of flower, and then sticking with that flower species because it’s familiar and easy. Some bee species intentionally seek pollen from certain plant species right from the start. For example, Colletes aberrans, with the unimaginative common name “aberrant cellophane bee,” seeks out pollen from the genus Dalea. Just as you’ll find monarch caterpillars munching on milkweed and nowhere else, you’ll find Colletes aberrans foraging for food on prairie clover flowers. It’s not just a preference, it’s effectively a dietary requirement.
The Polylecty–Oligolecty Spectrum: Degrees of Pollen Specialization
Among native bee species, some forage on any flower species they can get at effectively. Our many species of bumblebees are one example. They fall near the polylecty (meaning: gather from many) end of the spectrum. Any pollen and nectar will do. Aberrant cellophane bees fall near the oligolecty (gather from few) end. Bee species at the extreme oligolectic end of the spectrum, collecting pollen from just one species, are described as monolectic, although that term is sometimes also applied to bees who take pollen from only a single genus, like aberrant cellophane bees on Dalea species.1
Prairie clover gets a benefit from aberrant cellophane bees because they focus just on prairie clover flowers. No side-trips to other flowers, no pollen wasted by being delivered to the wrong address.
Bee Lawns and Pollen Specialists
As an effort to make lawns less harsh on the environment and more useful to pollinators, bee lawns are an improvement on pure turf grass. But how many North American bee species are specialists on European white clover, creeping thyme, or dandelions? These plant species can benefit generalist bees, but offer virtually nothing for specialists. Thirty to 50 percent of native bees specialize to some degree. For the greatest support to bee diversity and nutrition, your efforts will pay off much more if you plant gardens that include a wide diversity of native plant species.
What’s in it for the Bees?
The benefits to a bee who’s a pollen specialist are still being researched. It may be that the pollen of certain flowers is easier to digest for certain bee species, or that it provides critical micronutrients not found in other pollen.2 Or it may be that specialist bees simply don’t recognize other flowers as food sources at all. Bees respond to olfactory cues in the scent emitted by flowers, and some scents may be interpreted as “yum,” while others are more like “yuck,” or perhaps just “meh.”
Dave Crawford is a retired Minnesota State Park naturalist who has replaced most of his lawn with nativeplants. He documents visiting pollinators for fun and as a way of learning more about them. All photos are courtesy of the author.
1 In North America, one example of a thoroughly monolectic species is the pickerelweed shortface bee (Dufourea novaeangliae), which forages only on the species Pontederia cordata, pickerelweed.
2 Some bee species have specialized shapes to their legs that are perfectly matched to the most efficient way to loosen pollen from just one or a few flower species.