Winter bumble bees and wildflowers

This video and photos in this blog post show numerous bumble bee species foraging on non-native heather (Erica spp.) plants in our garden on February 24, 2016.

It’s still winter in the Klamath-Siskiyou, but the warm, spring-like days this February have brought out the bumble bees! Bumble bees are some of the first bees seen in the spring because they are specially adapted to be active in colder weather than most other bees.

Early emerging bumble bees are hard pressed to find flowers in February, but there are some native plants flowering already that they can utilize. I have seen snow queen or spring queen (Synthyris reniformis) and Nuttall’s toothwort or spring beauty (Cardamine nuttallii) blooming in the canyon I live in, along with several different species of willow (Salix spp.). The first Indian warrior (Pedicularis densiflora), gold stars (Crocidium multicaule) and native violets (Viola spp.) are all blooming in the Klamath-Siskiyou at low elevations, and the grass widows (Olsynium douglasii) will be blooming soon on sunny slopes and rock outcrops. For the bumble bees, spring will soon begin in earnest.

Bumble bees provide excellent pollination services for the diverse native plant species in our region, and this relationship and interdependence is crucial for the survival of imperiled native plants and pollinators alike. If you want to manage your land or garden for pollinator conservation the best thing you can do is plant flowering native plants that provide pollen and nectar throughout the growing season: early season, mid season, and late season flowers.

Bumble bees are classified in the genus Bombus. The Pacific Northwest is home to many native species of bumble bees, broken down into the following groups: the red-tailed group, the striped group, the black-tailed group, the whites, the yellow-faced bumble bees, and the cuckoo bees.

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Bumble bees of the Pacific Northwest identification chart created by The Xerces Society for Invertebrate Conservation

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Bumble bees of the Pacific Northwest identification chart created by The Xerces Society for Invertebrate Conservation

The Bees In Your Backyard: A Guide to North America’s Bees gives the following information about bumble bees:

  • The name Bombus comes from the Greek word bombos, which means “a buzzing sound,” referring to the low hum these bees make as they fly gracefully around flowers. The common name “bumble bee” can be traced back to the word bombelen in Middle English (AD 1200-1500), which means “to hum.” In fact, prior to the 1920s, bumble bees were more often called “humble bees,” also a reference to the soft droning inherent in their foraging activities. The term “humble bees” was used by both William Shakespeare in A Midsummer Nights Dream and by Charles Darwin in On the Origin of Species. A few popular articles in the 1920s about Bombus referred to them as “bumble bees” and the new name took.Scan 20
  • Bumble bees are among the few bees native to North America that are truly social, with a queen and workers.
  • Like European honey bees, bumble bee workers collect copious amounts of nectar, which they bring back to the hive for storage. Unlike honey bees, however, the bumble bee workers do not dehydrate the stored nectar, turning it into honey. Instead this nectar is used by bumble bees, along with pollen, to feed the developing young. Because bumble bee hives begin anew each year, there is no need to store large amounts of nectar as honey to sustain the workers through the winter the way that honey bee colonies must.
  • Studies have shown that for many crops, pollination by bumble bees produces bigger fruit, faster fruit set and larger yields than other pollination methods, most specifically honey bee pollination. First, bumble bees have a distinct advantage over European honey bees when it comes to retrieving pollen from some plants: they can buzz pollinate. They are therefore much more effective pollinators of some important crops, specifically with flowers requiring buzz pollination. These plants include tomatoes, peppers, eggplants, potatoes, and even some berries like blueberries. Second, bumble bees have been shown to be faster workers than honey bees, often visiting twice as many flowers per minute. Finally, researchers have estimated that bumble bees will do at least eight times more work than a honey bee because bumble bees can remain active in cold temperatures, and they can carry more pollen.P1250344
  • Bumble bees have special adaptations that allow them to be active in colder weather and colder climates than most other bees. In addition to their thick and insulating coat of hair, bumble bees often bask in the sun to warm themselves before they head out to forage. When sun and fuzz aren’t enough, bumble bees can actually generate heat internally by shivering their flight muscles. These bees can uncouple their wings from their flight muscle, allowing them to contract the muscles without flapping their wings. Those muscle contractions can raise the internal temperature of the bee, making them significantly warmer than their surrounding environment. In fact, bumble bees can’t take off and fly until their flight muscles are above 80 degrees; by shivering their flight muscles to warm up, they can actively forage in temperatures much too cold for other bees.
  • Unlike honey bee queens, a bumble bee queen lives for only a single year. This annual cycle generally keeps bumble bee hives much smaller than the hives of honey bees. Most mature bumble bee colonies consist of fewer than 200 bees, although some can have as many as 1000 individuals. For comparison, European honey bees may have around 60,000 bees in a single colony.
  • Most bumble bee species make their nests in the ground, often in preexisting cavities like abandoned rodent burrows, in piles of wood, or in leaf litter.

The following is an excerpt from The Xerces Society’s publication: Conserving Bumble Bees: Guidelines for Creating and Managing Habitat for America’s Declining Pollinators

 

Competition with Honey Bees

The honey bee (Apis mellifera) was introduced to North America by European settlers in the early seventeenth century. The honey bee is extremely important to our agricultural system, yet its populations have declined steadily since the mid twentieth century. Many efforts to support honey bee populations are in line with bumble bee conservation. However, recent research has shown that competition with honey bees reduces bumble bee foraging efficiency, worker size, and reproductive success. As such, bumble bees in close proximity to honey bee hives may be experiencing additional pressures in an already difficult landscape. A single honey bee hive can contain over 50,000 bees, who collectively remove hundreds of pounds of nectar and tens of pounds of pollen from an area in a single year. Whether this is testing the limits of the available flowering resources is unverified. However, there is no doubt that such a significant removal of resources must represent a substantial proportion of the available pollen and nectar, especially during a period of limited flower abundance.

Klemens and Volkmar showed that the presence of honey bees force bumble bees off flowers, and change their foraging times. While reproductive success was not measured in this study, any event that causes decreased efficiency of foraging trips is likely to be detrimental for bumble bees.

In addition, it has been shown that pollen is a vector for disease transmission between honey bees and bumble bees. Thus, where bumble bees are visiting the same flowers as honey bees, they face an increased risk of infection. Diseases from some pathogens can lead to fewer new queens produced by the colony. Since honey bees are present virtually everywhere there are flowers in North America, it is nearly impossible to avoid interactions between honey bees and bumble bees. However, if land managers have the option to limit these interactions by restricting honey bee hives from natural areas managed for biodiversity, it is strongly recommended.

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