Native bees in TexasBy Michael Warriner on June 10th, 2012
Although non-native honeybees tend to garner the most public attention, there are actually several hundred bee species that are native to Texas — species that were here long before the honeybee and that are essential to the state’s diverse native plant communities.
Bumblebees are among the most familiar of these. Their black and yellow bodies are easy to recognize as they buzz from flower to flower. Like honeybees, bumblebees are social insects that live in colonies comprised of a queen and her daughter workers that will protect their nest site if disturbed. Bumblebee colonies are much smaller in size though, containing only 100-200 workers compared to the 15,000 or more workers in a honeybee colony.
Social bees are very much the exception when it comes to Texas bee diversity. Most native bees in the state are solitary with individual females establishing and provisioning nest sites all on their own. Unlike honeybees and bumblebees, solitary bees do not defend their nest sites. Solitary bees tend to be small and less frequently observed than their larger, social cousins. Although less well-known, solitary bees such as leaf-cutter bees (Megachile sp), mason bees (Osmia sp), mining bees (Andrena sp), squash bees (Peponapis sp), and sunflower bees (Diadasia sp) are responsible for a significant amount of pollination in agricultural and ecological systems.
Pollination is one of the most fundamental processes sustaining agriculture and natural ecosystems. In Texas, most plant pollination is carried out by bees. The European honeybee (Apis mellifera) is our most well-known species, first brought to North America around 380 years ago by European colonists. Its more notorious relative, the Africanized honeybee, has spread across Texas and now constitutes a significant public health threat.
The European honeybee has been in a well-documented decline in the U.S. since the 1950s as a result of agricultural intensification, diseases, parasites, and pesticides. Unabated loss of this bee will have significant repercussions for large-scale, intensive agriculture to be sure. However, it will not be an ecological calamity. The conservation challenges facing native bees are where the real concerns for natural ecosystems lay.
Many native bees are now thought to be experiencing population declines. Research has documented range reductions for several bumblebee species across North America. Franklin’s bumblebee (Bombus franklini) has been petitioned for protection under the U.S. Endangered Species Act. Eighteen native bees are considered species of greatest conservation need by Texas Parks and Wildlife Department.
A principal factor driving native bee decline is widespread habitat destruction, specifically the loss of flower-rich grasslands, savannas, and woodlands. Open natural communities represent optimal habitat for native bees as they support diverse assemblages of flowering plants and relatively abundant nest sites.
Even if native bees are declining, why should we be concerned? The answer to that question is simple once one realizes most native plants in North America require pollination by insects to produce fruit and viable seed; fruit and seed that, in turn, support entire terrestrial ecosystems. That’s not even taking into account the dozens of agricultural crops we humans use that require insect pollination.
Of all the insects that visit flowers, from beetles, butterflies, and wasps, bees are the most important pollinators.
Two traits make bees preeminent pollinators. First, they purposefully collect pollen to feed their offspring. The act of foraging for this food source results in the transfer of pollen from flower to flower. During a single day, a female bee may visit several hundred flowers, depositing pollen all along the way. Second, bees tend to be specific about the flowers they visit. During a foraging trip, a female bee may only visit the flowers of a particular plant species. The benefit of such foraging preferences is that the plants’ pollen is not deposited on the flowers of a different plant species and wasted.
Native bee pollination is critical to the maintenance of Texas diverse ecosystems. Many of the berries, nuts, and seeds consumed by birds, mammals, and other insects are the result of bee pollination of native woody and herbaceous plants. Along with their substantial ecological contributions, native bees have proven to be more efficient and effective pollinators than honeybees for such agricultural crops as apples, blueberries, pumpkins, squash, tomatoes, and watermelons.
The pollination service provided to U.S. agriculture by native bees has been estimated in excess of $3 billion annually. The added benefit to farmers from native bees is that their services are essentially free if adequate natural habitat is maintained around farm fields to support healthy populations of these pollinators.
Native Bee Needs
Native bees have two basic needs: food in the form of nectar and pollen from flowers and a suitable place to nest and lay eggs. By meeting one or both of these needs, private landowners, including home gardeners, can make contributions to native bee conservation.
While some native bees are only active for short, discrete periods, most species benefit from a diverse array of native herbaceous and woody plants that provide a succession of flowers from spring into early fall. Bumblebees, for instance, require a near continuous supply of nectar and pollen for up to nine months to complete colony development.
The nesting habits of native bees can be classified into two categories: deadwood-nesters and ground-nesters. The majority of native bees in Texas are members of the latter group and either nest in burrows dug of their own labor in bare ground, in preexisting underground cavities (rodent burrows), or within clumps of vegetation. Species that nest in dead wood generally live in tunnels left by wood-boring beetle larvae in standing dead trees, under the loose bark of downed wood, or in hollow stems.
Identify and Protect
Now that you know the basics of what native bees need, the next step is recognizing those resources on your property. Survey your property to see if it already contains patches of flowering herbaceous plants or groups of flowering shrubs and trees. Once you have identified likely sites, you can protect them and adjust management practices to preserve them over time.
Observe these patches at different times of day to see which plants are heavily used by bees and other flower-foragers. These are areas to protect within the framework of your property’s management plan.
Existing nest resources will be a little harder to recognize than patches of flowers, but general nesting habitats across a property can be identified and preserved. The safe and prudent retention of standing dead trees and downed wood will not only provide natural nesting sites for cavity-nesting bees but a range of other wildlife.
Well-drained, sparsely vegetated patches of bare ground are preferred nesting habitat for many solitary bees. While sparsely vegetated ground may seem unsightly, there are reasons some areas don’t support much vegetation (thin soils, deep sands). Avoid ground disturbance (disking, tilling) in these sites to maintain and promote nesting aggregations of solitary bees.
Bumblebees, on the other hand, do not dig their own nests but rather take up residence in abandoned rodent burrows or tussocks of grass in areas of thick herbaceous vegetation. If possible, let open, grassy portions of your property grow unchecked and undisturbed for a few years.
Management practices, such as burning, grazing, and mowing, should be implemented with native bee needs in mind as these techniques have the potential to reduce or eliminate food and nest sites. Grazing should be low intensity, short duration, and limited to the end of the growing season to protect nectar and pollen sources. Mowing should also be restricted to the very end of the flowering season to maximize availability of these resources to native bees. Prescribed burns should be conducted in the fall and winter. It is best to avoid applying any management practice to an entire site. Rather, only treat a portion of the property, say one-third to one-half. Untreated sections will serve as critical refugia for species to recolonize the burned, grazed, or mowed portion of the property.
A survey of your property may reveal deficiencies in available foraging and nesting resources. There are steps you can take to augment these. Increasing the diversity of flowering plants is one of the more enjoyable and rewarding steps. Texas native plants are your best choices as these are the species native bees have used for hundreds of thousands of years and are the best adapted to the state’s climate.
If you are creating a backyard flower bed or restoring a former pasture, work to establish plantings that will provide flowers over spring, summer, and early fall. Robust sources of nectar and pollen during these three seasons will help to meet the needs of a wide range of native bees, especially those with long-lived colonies like bumblebees. Try to include as many plant species as possible since native bees vary in their preference for floral color, shape, and size.
A great online tool for determining which native plant species are best for your ecoregion of Texas can be found on The Pollinator Partnership’s website (http://www.pollinator.org/guides.htm). Simply type in your zip code and you will be directed to a downloadable ecoregional-specific planting guide.
The second piece of the puzzle in augmenting native bee populations is to increase available nesting habitats. Ground-nesting solitary bees need access to sunny, well-drained patches of bare ground. Suitable sites can be developed either by manually clearing vegetation from a small area or by creating a sand pit. For the latter, dig down one to two feet in an open, well-drained spot and fill with a sandy loam mix. Be sure to keep this area relatively free of vegetation. Keeping some portion of your flower bed free of mulch, exposing soil, is a quick and easy way to provide habitat for ground-nesting bees.
A lack of deadwood can be addressed by installing nest blocks, houses for bees essentially. Nest blocks should be constructed from untreated lumber (2×4, 4×4, to 4×8) and eight or more inches in height. Holes of varying diameters, from 1/4”to 3/8”, should be drilled into the blocks spaced 3/4” apart. Don’t drill completely through but rather about 1/2” from the back of the block. Attach a roof to provide protection from intense sun and rain.
Blocks should be mounted at least three feet above the ground and firmly secured to a building, fence, or post, so as not to sway in the wind. The face of the nest block should be oriented to the southeast to catch the morning sun.
Although there are inherent dangers with having honeybee colonies in suburban and urban landscapes, bees that use nest blocks are all solitary species that do not defend their nests and are therefore much safer to have around your home. If you are lucky, leaf-cutting and mason bees will fill the drilled blocks with eggs, capping the entrance with mud or plant fibers. Blocks can be left in place throughout the winter or brought into an unheated garage to protect next year’s crop of solitary bees from hungry woodpeckers. Be sure to return blocks outdoors in late winter or very early spring to allow the bees to exit their chambers.
These guidelines and suggestions are not exhaustive and are, in fact, just the tip of the iceberg. The Xerces Society for Invertebrate Conservation has been leading the way in the recent push to conserve native bees. They have produced a wealth of detailed information that is available online (http://www.xerces.org/bringbackthepollinators/) and in print (Attracting Native Pollinators: Protecting North America’s Bees and Butterflies, Storey Publishing). For those interested in Texas-centric bumblebee efforts, visit http://texasbumblebees.com to learn more about these pollinators.