By Nancy Brooks, Extension Master Gardener
I learned about a resource, Conserving Bumble Bees by the Xerces Society, by participating in the Plant NOVA Natives series called Grow Natives sponsored by the Lewis Ginter Botanical Garden in Richmond. Each session has provided excellent information and many resources like Conserving Bumble Bees, highlighted by speaker Celia Vuocolo.
Conserving Bumble Bees is a very useful document, identifying nearly 50 North American bumble bee species that are an essential part of our pollinator communities because they visit a wide variety of blooming plants, have a long flight season, and fly in low light levels and in cool temperatures (their big, furry bodies can keep warm by generating heat, which is called thermoregulation and which is uncommon among bees).
The Xerces Society emphasizes that we can help bumble bees thrive by providing three key types of habitat: plants offering pollen and nectar on which to forage, nesting sites, and places to overwinter. Extension Master Gardeners encourage the public to create, protect, restore, and enhance high quality bumble bee habitat. By implementing these practices and creating corridors between habitat, we can help slow, stop, and reverse the recent decline of bumble bee populations.
Plants, Pollen, and Nectar
First, bumble bees need rich sources of pollen and nectar, which are provided best by perennials – not annuals — because of their higher quality nectar. Bumble bees can see purple, blue, and yellow flowers more clearly than red. Their tongues are of different lengths, and so different bee species need flowers with corolla tubes of different lengths. Some nectar-robbing bees even pierce a long corolla and steal the nectar.
Bumble bees are important generalist pollinators of some of our favorite fruits and vegetables like blueberries, eggplant, peppers, tomatoes, and zucchini. But bumble bees’ important role is threatened by homeowners who have access to toxic pesticides and insecticides with little regulation of their use.
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Second, we and our neighbors can make a direct contribution to bumble bee habitat by building a refuge that includes nesting sites. The top five nest locations are bird box, cavity in rock wall, compost pile, under a manmade building like a shed, and hole in the ground. Our gardens, parks, and managed natural areas can be significant refuges.
Finally, we and our neighbors can make a direct contribution to bumble bee habitat by leaving valuable overwintering habitat in place in the fall, rather than cleaning up our gardens too neatly. Leave the leaves, leaf litter, brush, fallen logs, and grass tussocks that are all dry and dark and attractive to bumble bees as winter havens.
Conserving Bumble Bees includes these additional resources:
Regional guides that list the many species found in North America, including our local common eastern bumble bee.
Plants for bumble bees by each region of the country. For example, Virginia is grouped with the Southeast and the 10 plants listed for the Commonwealth are: Wild azalea, Rhododendron canescens; Spotted beebalm, Monarda punctata; Sundial lupine, Lupinis perennis; Swamp rose, Rosa palustris; Butterflyweed, Asclepias tuberosa; Common buttonbush, Cephalanthus occidentalis; Field thistle, Cirsium discolor; Narrowleaf mountain mint, Pycnanthemum tenuifolium; Tall blazing star, Liatris aspera; and Great blue lobelia, Lobelia siphilitica. Together, these 10 plants provide a bloom period from March to October and provide a variety of colors that bumble bees prefer. This list is augmented by a list of small trees and shrubs that flourish nationwide, as well as a list of garden plants that flourish nationwide and support bumble bee habitat.
And More Bees for Pollinators Week…
Scientists continue to share new data about bees. Most recently, Delaware’s Mt. Cuba Center sponsored research about bees by Matthew J. Sarver, Principal, Sarver Ecological, LLC. His executive summary of the Mt. Cuba Native Bee Survey 2018-2019 Final Report states that this study of Mt. Cuba’s gardens and outlying natural lands documented 3,493 individual bees of 135 species during 2018-2019. He recommends these practices as most useful to the greatest variety of bees:
- Maintain high floral area for important host species of rare and uncommon bees, including Polemonium reptans, Uvularia grandiflora, Penstemon spp., and others.
- Increase floral area of the straight species Heuchera americana to support the regionally significant Colletes aestivalis population and promote americana as a straight species in the nursery trade.
- Focus heavily on increasing the floral area and diversity of late summer and fall composites (Solidago, Symphyotrichum, Vernonia, Helianthus, Cirsium, etc.) as appropriate. Helianthus is likely a particularly important gap to fill as it is underplanted and does not seem to “turn up” on its own very often.
- Plant woody species such as Salix, Cornus, and Rubus that support bee diversity as well as specialist bees in shrub and edge plantings.
Hatfield, Rich, Sarina Jepsen, Eric Mader, Scott Hoffman Black, and Matthew Shepherd. Conserving Bumble Bees: guidelines for creating and managing habitat for America’s declining pollinators. Xerces Society for Invertebrate Conservation: Oregon, 2012.
Sarver, Matthew J. 2020. Mt. Cuba Native Bee Survey 2018-2019 Final Report. Report to Mt. Cuba Center. Sarver Ecological, LLC: Wilmington, DE.