American Bumblebee

Growing up in Northwest Missouri, I distinctly remember insects being everywhere. Butterflies, bees, fireflies and many others were all plentiful and easy to find. Today, this is not the case, as more and more species find themselves in very real danger of becoming endangered and ultimately extinct. It seems bees are suffering population declines more than any other species of insects. There are more than 4,000 species of bees across North America, with more than a quarter of the bumblebee species in some state of decline, and nearly half of the other bee species listed as imperiled, threatened or endangered. These are truly frightening statistics! 

The American Bumblebee, once a widespread species often encountered in open fields, grasslands and agricultural areas, is now classified as threatened, critically threatened or endangered in all its range, having experienced population declines as much as 90% since the year 2000. They are currently extirpated from eight Northern states; Maine, Idaho, New Hampshire, Oregon, Rhode Island, Vermont and Wyoming. They are still commonly encountered in part of their range, mostly in southern states from Florida to Texas and north to Colorado to include many of the Midwest states like Missouri. Even though this bee still buzzes freely over a wide swath of Missouri, that does not mean we should become lackadaisical about its presence, in short order it can disappear leaving a void where it once survived. As a species that was described before our nation gained its independence, it would be sad indeed to lose it. 

The name of American Bumblebee is a bit misleading, as they are not the most widespread of the native bumblebees, although its historic range did include much of the United States and Southern Canada. These are a large bumblebee, with the queen measuring more than an inch in length, workers and males easily an inch in length or more. Males and females are dimorphic, with females having black and yellow banded abdomens typical of many bumblebee species, whereas males have all yellow abdomens that may or may not have a small rusty patch located at the end. This time of year, the new queens and males are spotted pollinating a wide range of flowers, such as thistle, goldenrod, clover and vetch, often favoring the purple flowering plants over others. These queens will mate and spend the winter hidden away in leaf litter or in rotten logs. The males and other members of the hive will perish. In early spring, as temperatures begin to rise, queens will seek pollen and nectar from any available plants and begin setting up a new nest. These bees’ nest above ground in thick bunches of grass or hay bales. They will sometimes use old bird’s nests, or even nest underground, utilizing old rodent burrows. Man-made items have been known to be used as well, such as cinder blocks, buckets and abandoned sheds.

The new queen will care for the developing workers until they reach adulthood. At this point she will remain home and continue to lay eggs while the workers keep the nest clean and care for their queen and her offspring. By summer’s end the nest may contain as many as two hundred workers. Occasionally female workers may produce their own eggs, which will develop without fertilization by a male, and will produce offspring destined to be males. The queen is often not tolerant of this behavior and will kill these workers. Maybe to reduce competition. Once the hive reaches sufficient size, the queen will shut off the hormones she utilizes to keep her female workers infertile and will begin laying eggs destined to be males and new queens. Squabbling among the workers and the queen is common, and by the end of summer the workers will attack their queen, stinging her repeatedly until she perishes. When the first cold weather of fall sets in, the infertile workers and males will all die, leaving only the newly bred queens that will overwinter and repeat the cycle all over again the following spring.

Like most wild creatures, they have predators who often prey upon them. Mammals like skunks, raccoons, and bears all prey on bumblebees and their food stores including pollen, nectar and larvae. Crab spiders, robber flies, and ambush bugs all feast on bees, and often hide among flowers to deceptively attack them as they forage for pollen and nectar. Sneakier still are the parasitoids, like many species of flies that attach themselves to the bumblebee in flight and lay an egg within the bee. The egg hatches inside the bee and feeds on the bee’s tissue from within. The bee will live almost two weeks under the onslaught of the feeding fly larvae. The fly then pupates and resides inside the bee throughout the winter as a fully developed adult. When spring returns, the fly emerges from the dead bee and seeks another bee to continue its lifecycle. There is also a nematode worm that parasitizes American Bumblebees. This parasite does not kill or even reduce its lifespan, but it does render the bee sterile.

Even though as much as 30% of bumblebees are parasitized by some sort of parasite, this is not the greatest threat these bees face. Humans and our activities are.  As open spaces are replaced by urban expansion and agricultural growth, the American Bumblebee finds itself struggling to survive.