Bumble Bees

One of the approximately 21 species of bumble bees native to the eastern U.S. Photo credit: Brian Martin, CC-0

There are approximately 250 species of bumble bees worldwide with approximately 50 of those being native to North America. According to Bumble Bees of the Eastern United States, 21 species occur from the east coast to the western boundaries of Minnesota, Iowa, Missouri, Arkansas, and Louisiana. Based on their maps, approximately a dozen of those species have the potential to be found somewhere in Kentucky.

Depending on the species, bumble bees range in size from approximately half an inch to one inch in length. They tend to be very furry which helps them be active earlier and later in the season than many other native species of bees. The ability to be active in the early spring and late fall is an important adaptation for the bumble bee life cycle.

Early in the spring, the new queen bumble bees emerge from hibernation. Each queen will find a nesting site such as an abandoned rodent burrow. She will gather pollen and nectar from nearby flowers then lay her first round of eggs in the nesting site. The young queen will incubate the eggs until they hatch a few days later. She will then feed and incubate the young larva for a couple of weeks until they pupate. Much like a mother bird, the queen bumble bee will only leave her nest to gather more pollen and nectar to feed to her young. After approximately another two weeks as pupae, the young will emerge as adult female worker bees. The new worker bees then take over the duties of foraging for food and caring for the new eggs and larva produced by the queen. The colony will continue to grow and may reach up to a couple hundred bees in size by the end of the summer.

Highbush blueberries can provide yummy and nutritious berries for the birds and for us. Photo credit: Ken-ichi Ueda, cc-by

Towards the end of summer, the queen will begin producing male offspring and new potential queens. The males and potential new queens will leave the hive to find mates. After mating, the males will die and the newly mated queens will find places to hibernate through the winter. All of the bees in the original hive, including the original queen, will die by the end of fall. Bumble bees only live a year or less. The next spring, the new queens will emerge from hibernation and the process will begin again.

Bumble bees are important native pollinators that forage for nectar and pollen from a wide variety of plants. They are also important pollinators for agricultural purposes. In fact, bumble bees are actually more efficient pollinators for many of our favorite crops (e.g. tomatoes, peppers, blueberries) than honey bees. One reason why they are such efficient pollinators of those crops is because bumble bees, unlike honey bees, are capable of buzz pollination.

With buzz pollination, the bumble bee grasps the anthers of the flower and vibrates them at a certain frequency. The vibrations stimulate the anthers to release clouds of pollen that tumble down onto the bumble bee and gets stuck in its hairs. The bumble bee grooms much of the pollen off and packs it into its pollen baskets to take back to the colony for feeding to the larva, but some of the pollen is missed and is transferred to the next flower that the bee visits. Because bumble bees are such efficient pollinators of some crops, there is a growing trend to commercially raise bumble bees and ship them across the country for pollination purposes. In some cases, they are used in addition to honey bees and in some cases they are used instead of honey bees.

The endangered rusty-patched bumble bee is one of 21 species of bumble bees found in the eastern U.S. Photo credit: USFWS Midwest Region, cc-by 2.0

Despite how important bumble bees are to the natural ecosystem and to agriculture, we know relatively little about many bumble bee species. Many species appear to be declining, but scientific studies to quantify population numbers and ranges of individual bumble bee species have been few and far between. Population declines are suspected to be due to a combination of factors including habitat loss, pesticides, and introduced pests and diseases. Many researchers believe that some of these introduced pests and diseases are the result of bumble bees being shipped to Europe for commercial production in the 1990s and then being brought back to the U.S. to be used for pollination. While in Europe, the bees were accidentally exposed to and infected with the new pathogens which they inadvertently brought back to the U.S. and spread to the wild populations. New research is also showing that some of the viruses that are affecting honey bee populations can infect bumble bees as well. There is still much to be learned about bumble bees and the factors that threaten them.

To help address the lack of scientific data regarding bumble bee population numbers and ranges, a new citizen science project, Bumble Bee Watch,  has been established. The project asks individuals to create a free account, then take pictures of the bumble bees they see. After uploading the pictures to their account, the individuals can try to identify the bees based on information provided through the website. An expert will then verify the identification and the information will be added to the database to help document the ranges and populations of our many different bumble bee species. If you are interested in helping the bees, this is an easy way you can help scientists learn some of the basic information we lack about one important group of our native bees.

This article was part of Shannon’s original Kentucky Pollinators and Backyard Wildlife blog which evolved into the blog for Backyard Ecology.

Backyard Ecology: Exploring Nature in Your Backyard
Nature isn’t just “out there.” It’s all around us, including right outside our doors. Hi, my name is Shannon Trimboli, and I am the host of Backyard Ecology. I live in southcentral Kentucky and am a wildlife biologist, educator, author, beekeeper, and owner of a nursery specializing in plants for pollinators and wildlife conservation. I invite you to join me as we ignite our curiosity and natural wonder, explore our yards and communities, and improve our local pollinator and wildlife habitat. Learn more or subscribe to my email list at www.backyardecology.net.

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