Bumblebees Part 2: Bumblebee Watching

Previous installments: The Funny Fuzzy Bumblebee and Bumblebee Lives

FROM SPRING THROUGH SUMMER, sometimes as late as October, worker bumblebees never stop looking for food for their growing nest. Those “fur coats” they wear allow them to do their “work” in much lower temperatures than do many other pollinating insects, such as the non-native honeybees. They often can be seen out even early in the day and late into the afternoon.

Watching these little ladies at work offers no end of opportunities for amateur naturalists. You can use color photos in the back of Brian Griffin’s book, Humblebee Bumblebee: The Life Story of the Friendly Bumblebees and Their Use by the Backyard Gardener, to identify many of the more common species.

It’s sometimes also possible to lure bumblebees into nesting in a nest box you provide for them. Griffin’s company, Knox Cellars, sells a wooden “Humble Bumble Home,” with instructions. The nest box even comes with an acrylic panel that allows you to peek into the nest itself.

Get to know your garden’s bumblebees and you will soon marvel at the intelligence of even the smallest creatures. According to my other favorite bumblebee book, Bernd Heinrich’s Bumblebee Economics, individual bumblebees learn how best to get pollen and nectar from specific flower types. Thus, for example, one bee will learn that she can get pollen from wildflowers in the carrot family, such as Queen Anne’s lace, by walking quickly across the flat surface of the bloom, pushing her body down against the tiny flowers. Another will learn to collect pollen from wild roses, by grasping a group of anthers with her front legs and shaking them.

As a result, individual bees “specialize” in gathering nectar and pollen from specific species of plants. Young bumblebees tended to specialize in “easy access” flowers, such as goldenrod, Heinrich found, even though these often don’t produce large amounts of nectar. Older bumblebees, however, tend to specialize in flowers that are rich in nectar but hard to get into.

For instance, the nectar in monkshood blossoms (Aconitum spp.) is abundant but stored in modified petals that are very difficult for insects to figure out. By and large, older bumblebees are the only pollinators clever and persistent enough to figure out how to get to this nectar. By excluding all pollinators but bumblebees, but offering a handsome nectar “reward” to those who do solve the puzzle, monkshood blooms ensure that certain bumblebees will become “monkshood specialists,” Heinrich notes. This in turn makes it likely that each bee will go directly from one monkshood plant to another, ensuring cross-pollination.

Another example of the way pollinators interact with plants is the relationship between bumblebees and foxglove (Digitalis purpurea). According to Heinrich, the flowers of foxglove begin as male and then turn into female because the stigma mature more slowly than the anthers do. Hence male flowers tend to be at the top of the plant (more recent blooms), with females (older blooms) at the bottom. Older blooms also tend to have more nectar, so bumblebees characteristically visit the lower, nectar-rich flowers of foxglove first, working their way up the plant. This characteristic foraging pattern helps the bees to avoid visiting the same blooms twice, and it also tends to ensure that the bees will invest their foraging time in the most nectar-rich flowers. But it also helps the plant, because the bees go directly from the male (upper) flowers of one plant to the female (lower) flowers of the next plant.

Both Griffin’s and Heinrich’s books are full of fascinating information such as this, and I urge you to read at least one of them. Griffin’s is probably the better book for beginners, with Heinrich’s being great fun for those who want to understand bumblebee behavior in greater depth.

This series of posts on bumblebees is taken from an article I originally wrote for Northwest Garden News.