In through the back door
While traipsing through the farmer’s market last weekend, I met a beekeeper with an interesting question. Having heard that honey bees are poor pollinators of alfalfa, she wanted to know where alfalfa honey comes from. How does that work?
Honey bees are, indeed, second-rate pollinators when it comes to alfalfa. When the bee sits on the keel of the flower—the bottom petal—the bee’s weight trips the spring-loaded central column. The column is a tight package comprised of the style and the anthers. When it trips, the anthers explode outward from the style, bop the bee over the head, and scatter pollen over the bee’s body.
Honey bees are annoyed by the tripping mechanism and soon learn to avoid it by approaching the base of the flower from the outside. From there a bee will prise the petals apart, reach down with its proboscis, and drain the nectary.
This process is called “nectar robbing.” Nectar robbing will provide the alfalfa honey you see for sale, but it will not pollinate the alfalfa flower because the column remains intact. If the plants are being grown for seed, it is the grower’s turn to be frustrated.
According to various sources, it takes the average honey bee forager between four hours and two days to learn the trick of gaining the prize without doing the work. Some growers address this problem by bringing in extra beehives under the theory that every day new foragers enter the workforce—neophytes that don’t know how to rob the nectar. By the time they learn, a new group of foragers will replace them. This is called pollination saturation.
Apparently, alfalfa seed growers in California have been using this technique for years. But growers in Washington and Idaho use a combination of the native alkali bee, Nomia melanderi, and the imported leafcutter, Megachile rotundata, instead of the honey bee to pollinate the fields.
Normally the leafcutter bees are trucked in from Canada, but lately—since California growers began using leafcutters as well—the price per gallon has skyrocketed. Seeking to control costs, the Northwest growers are becoming ever more dependent of the native alkali bee.
Honey bees are not alone when it comes to robbing nectar. Carpenter bees do it, and bumble bees do it too. In most cases it is not a tripping mechanism that deters the bee but the length of the flower’s trumpet. If a carpenter or bumble bee tongue is not long enough to reach the nectar, the bee will drill a hole in the base of a petal. And once a hole has been completed, other bee species feel free to use it as well.
Earlier this year I saw a honey bee sipping nectar from the outside of a camas flower, and I have also seen them robbing salvia. Bees are overachievers when it comes to creative problem solving, so I suspect nectar robbing is more common than we realize.