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July 2012

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The Secret Life of Bumblebees

Large and adorably fuzzy, these important pollinators help produce a bounty of Texas foods.

By Michael Warriner

Everyone knows the buzz that bees have been associated with human cultures for thousands of years. When we think of bees, we usually think of honeybees and their geometric hives full of honey. What many may not know is that honeybees are a relatively recent introduction to North America.

While the first European colonists brought honeybees here in the 1600s, Texas actually hosts hundreds of other bee species that are native. These bee species were here long before the honeybee and play critical roles in Texas’ diverse ecosystems.

Of all the state’s native bees, bumblebees are among the most familiar. Their fuzzy black-and-yellow bodies are easy to recognize as they buzz from plant to plant gathering nectar and pollen. Many of us who have chance encounters with bumblebees in gardens or parks likely know little about the different species that inhabit Texas, the role these insects play in producing some of our favorite foods or the threats endangering their continued survival.

 

Bumblebee basics

With the exception of a few species, bumblebees are social insects, with individual queens establishing colonies during spring. Bumblebee queens nest in or on the ground, taking up residence in tussocks of grass or abandoned rodent burrows. After her nest is established, she lays eggs that develop into her first cohort of daughter workers. The queen relies on these workers to forage for nectar and pollen, care for developing larvae and defend the colony against interlopers. At its peak, a bumblebee colony may contain up to 200 workers.

Unlike the colonies of European honeybees, which may persist for years, bumblebee colonies last for less than a single year, from spring into late summer or early fall. New queens, produced at the end of summer, are the only members of the colony to survive into the following year to begin the entire cycle again. The founding queen and all her workers perish as flowers diminish and temperatures drop.

Like honeybees, bumblebee colonies produce honey from sugar-rich flower nectar. Honey serves as a food reserve for the colony when nectar is in short supply or when cool, rainy conditions prohibit worker bees from foraging. The amount of honey produced by bumblebees is very small, nowhere near enough for human consumption. Since they store such small reserves, bumblebees require a nearly continuous supply of nectar and pollen from flowers over many months to support and complete colony development.

Losing bees

During the past few years we’ve heard about diseases, parasites and pesticides contributing to the decline of European honeybee colonies. To be sure, an unabated loss of honeybees would have significant repercussions for agriculture in this country. Less well-recognized are the conservation challenges facing bumblebees and other native bees.

Over the past 20 years, a substantial body of research has identified declines in bumblebee populations across Europe. Reductions in bumblebee diversity were first reported in the United Kingdom, where three species are now extinct. Eighteen bumblebee species are now considered threatened across their ranges in central and western Europe.

Declines for some North American bumblebee species have been documented only within the last few years. The rusty-patched bumblebee has disappeared from much of the eastern United States. Four species known to historically occur in Illinois have been lost from that state. In California, Franklin’s bumblebee has been proposed for listing and protection as a federally endangered species.

A principal factor driving bumblebee declines has been habitat destruction, specifically the loss of flower-rich grasslands. Grasslands represent optimal habitat for bumblebees because they typically support diverse assemblages of flowering plants and relatively abundant nest sites. Other potential contributors to species declines include the introduction of parasites and diseases into wild populations, pesticide use and competition with the European honeybee.

Why should we be concerned about the decline of native bees like bumblebees? As a group, these insects provide essential ecological services that help to maintain natural ecosystems — systems upon which hundreds of other native species depend. The majority of flowering plants in North America require pollination by insects. For many plant species to produce viable seed, an insect must move pollen from one flower to another, resulting in fertilization. Without pollinators, many plant species would fail to reproduce. Of all the insects that visit flowers, bees are the most important pollinators.

Two traits make bees preeminent pollinators. First, they purposefully collect pollen. Bees gather pollen to feed their offspring, and 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 might visit several hundred flowers, depositing pollen all along the way. Second, bees tend to be specific about what flowers they visit while collecting pollen. During a foraging trip, a female bee might visit only the flowers of a particular plant species. The benefit of a specific foraging preference is that the plant’s pollen is not deposited on the flowers of a different plant species and wasted.

Along with their substantial ecological contributions, native bees have proven to be more efficient and effective pollinators than honeybees for such agricultural crops as blueberries, pumpkins, squash, watermelons and tomatoes. The pollination service provided to agriculture by native bees has been estimated to be 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 farms to support healthy populations of these pollinators. However, more often than not, that natural habitat has been destroyed or degraded, and, like the honeybee, native bees are facing declines.

Texas bumble-watchers

Despite their critical roles in agriculture and natural ecosystems, bumblebees have gone relatively unstudied in Texas. The last published review of species in the state was in 1912, a century ago. There is a real need to evaluate the status of these insects in our state to assess how their populations are faring and to determine whether conservation actions are needed.

A first step in this process is simply recording where species are today. The website texasbumblebees.com enlists citizen “bumble-watchers” to aid in evaluating the state’s bumblebee fauna. Contributing to this process can be as simple as casually snapping images of bumblebees on flowers and recording the date and location. Visit texasbumblebees.com to learn more about this endeavor and how you can help.

Identification

As with many other insect groups, accurate identification of bumblebee species can be a little tricky. Within a species, individual color patterns can vary. Male bumblebees often have color patterns that differ markedly from those of females (queens, workers). Don’t let that intimidate you. There are only nine bumblebee species in Texas. That’s not an overwhelming number to get acquainted with. Just think of all the species bird-watchers have to learn. With some patience and study, you should be able to familiarize yourself with the bumblebees that occur in the state.

Fortunately, when collecting nectar or pollen, bumblebees can be easily observed (use binoculars if you want) and are relatively tolerant of humans. But remember, bumblebees can deliver a relatively painful sting. Unlike the European honeybee, they can also sting multiple times. Bumblebees that are away from their nests, foraging on flowers, are usually very placid and often oblivious to our presence, if they are not harassed. A bumblebee trapped in a butterfly net is a whole other matter. Never disturb a bumblebee colony if you discover their nest. They will defend it.

Bumble anatomy

All bumblebees are relatively large, fuzzy insects. Their body is divided into three segments — the head, thorax and abdo­men. The abdomen, in turn, is composed of six segments. Dense hairs, in varying combinations of black and yellow, cover most of their body. When attempting to identify a bumblebee, the features you will want to concentrate on most will be the pattern of black and yellow on the thorax and abdomen.

Identification basics

From spring into midsummer, female bumblebees will be the most commonly encountered sex. As a result, identification is simplified at this time of year with the absence of contrastingly patterned males. Once males emerge during the latter months of summer, identification becomes a little more difficult. The first step is assessing the thorax pattern of the bumblebee you are observing. Selection of one of the three thorax types narrows your options as far as abdominal color pattern is concerned. (A downloadable/ printable version of helpful illustrations can be found at texasbumblebees.com.)

Mistaken identities

A number of insects can be confused with bumblebees. Chief among these is the eastern carpenter bee. This is a large, native bee with the same general form as a bumblebee. It also has yellow hairs on its thorax. A major distinguishing feature can be observed on the carpenter bee’s abdomen. Carpenter bees have shiny, black abdomens with very few hairs, while bumblebees have furry abdomens.

Other insects that could be mistaken for a bumblebee include a day-flying moth, the snowberry clearwing and several species of bumblebee-mimicking robberflies. The snowberry clearwing hovers in front of flowers to feed, unlike bumblebees, which land and crawl over flowers to forage. The predatory robberflies that mimic bumblebees do not feed from flowers but rather prey on other insects, including bumblebees. Robberflies typically perch on vegetation, flying out as potential prey passes by.

Gardening for bumblebees

Conversion of natural habitats to less biologically diverse commercial and residential uses has eliminated a great deal of bumblebee habitat. You can enhance areas around your home for bumblebees and other native bees. Most of the methods used to create butterfly gardens also work well for native bees. In fact, it might be better to apply the broader moniker of “pollinator gardens” to such sites.

Bumblebees have two basic needs: food from flowers in the form of nectar and pollen and suitable nesting sites. By creating home garden plantings with appropriate plant species, you can increase foraging opportunities for native bees in your area. Attracting native bees is especially beneficial for those with backyard vegetable gardens.

The size of your pollinator garden will largely be based on the space you have available and the time you wish to spend tending to it. Even a small garden can provide valuable resources for native bees. In terms of location, a spot that receives at least six hours of sunlight is ideal. Plants in areas that receive more sunlight will produce more nectar than those in shady spots.

Bumblebees need a supply of nectar and pollen beginning in early spring and extending into late summer. When planning your bumblebee garden, choose plants that will bloom at different times of the year (spring, summer, early fall). Large clusters of the same plant species work much better in attracting bumblebees than singly spaced plants.

Insecticides used for garden pests can be toxic to bumblebees. In gardens strictly devoted to flowers, the insects that feed on the foliage of plants should be viewed as just another user group, along with bumblebees, and allowed to live their lives. Also avoid the use of herbicides in bumblebee gardens. The presence of “weeds” or unwanted plants in your garden can be minimized by hand-pulling or mulching. The absence of these chemicals from our landscapes will benefit bumblebees and a whole host of other species.

Plants native to Texas are the best choice for a bumblebee garden. Native plants have adapted to the often extreme conditions of a Texas summer and typically, once established, require much less care than non-native plants. Heirloom varieties of some plants and herbs are also acceptable for bumblebee gardens. They all provide a good source of nectar and pollen for bumblebees. Plants to avoid for bumblebee gardens include horticultural varieties and double-flowered hybrids (marigolds, roses). These plants have been bred for showy flowers in place of the structures that produce pollen. They also produce little to no nectar.

Given Texas’ geographic extent and diverse landscape, it would be impossible to provide a short list of suitable plants for bumblebees. Plant species for home landscapes in Houston are probably not suitable for the gardener in El Paso. Fortunately, the nonprofit Pollinator Partnership (www.pollinator.org) has produced very detailed, regionally specific plants lists for bees in Texas.

 


Related stories

The Trouble With Bees

Keep Texas Wild: What's the Buzzzz? (PDF)

Wild Thing: Big Buzzer


Related resources

TPWD news release: Pollinator Week in Texas

Bee resources at Pollinator Partnership

 

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