Native bees are essential to ensure a healthy, productive garden.
You’ll harvest more and bigger fruits and vegetables if you have enough pollinating bees visiting your garden. In some cases, better pollination even means faster maturity and better flavor.
Cornell University researchers have found that bee-assisted pollination of strawberries can increase fruit size up to 40 percent. Other crops that depend upon native bees for pollination include tomatoes, peppers, eggplants, pumpkins, squash and melons, plus most berries and tree fruits. But heavy reliance on pesticides, loss of habitat and monoculture crop systems have decimated pollinator populations.
“Monoculture makes it impossible for any bee — native or otherwise — to keep year-round populations sufficient for pollination,” says David Green, who maintains the native bee Web site www.pollinator.com. “A modern orchard has such a flush of bloom in spring that the pollination task is overwhelming. The rest of the year, it’s starvation or even a toxic environment.”
Besides avoiding pesticides, you can support native bee populations by protecting natural areas on your property, leaving field and road borders un-mowed to provide habitat for ground-nesting bees, and planting or preserving stands of native flowering plants (that the bees use for food) in pastures and hedgerows. A diverse selection of flowering plants and food crops ensures that pollinators have a steady supply of nectar and pollen throughout the growing season.
Take a close look at the flowers in your garden and you will quickly see that honeybees, which are native to Europe, have plenty of company, including numerous native bee species with specialized talents. But while honeybees are commonly protected by a beekeeper, native bees have no human guardians. This is why it’s important to help build native bee populations in your own area.
Like honeybees, native bees feed on nectar while gathering pollen to take back to their nests as food for their young. In the process, they pollinate flowers, often doing a better job than honeybees on certain crops such as apples, berries, alfalfa and almonds. Bumblebees are the preferred pollinators for greenhouse-grown tomatoes, and pumpkin growers from Wisconsin to Alabama are recognizing the value of squash bees — short-lived native species that often outnumber honeybees visiting squash blossoms, even when honeybee hives are nearby. In areas where cool temperatures limit honeybee activity during the spring blooming of fruit trees, native mason bees do the job because they are better adapted to cool weather.
Pollination in some crops is a collective effort among different species, however. Researchers at Ohio State University found that 18 species of native bees were doing most of the pollinating work in nearby strawberry fields.
These native bees don’t produce honey, and they can’t be reared in managed hives. But when they are given even small patches of suitable habitat, such as a fence row or diverse garden, some of the 4,000-plus species of native bees will show up.
“In a 20-acre woodland park that includes trees and flowers and that hasn’t been sprayed with pesticides, there may be 100 species of native bees present on a summer day,” says Jim Cane, research entomologist at the U.S. Department of Agriculture’s Bee Biology Lab in Logan, Utah.
According to the National Sustainable Agriculture Information Service, the following native bees are particularly good pollinators of certain crops, although they pollinate other flowering plants, as well:
Alkali bees: onions, clover, mint and
Bumblebees: blueberries, tomatoes, eggplants, peppers, melons, raspberries, blackberries, strawberries and cranberries
Carpenter bees: passionfruit, blackberries, canola, corn, peppers and beans
Leafcutter bees: legumes, especially alfalfa, and carrots
Mason bees: almonds, apples, cherries, pears, plums and blueberries
Shaggy fuzzyfoot bees: blueberries and apples
Squash bees: squash, gourds and pumpkins
It’s also important to understand that male bees can’t sting (a bee stinger is a modified egg-laying organ), and females won’t sting unless they are provoked. “They have no honey to protect, so they are not built to defend themselves from mammalian predators,” Cane says. If you find that you like sharing the company of native bees, or you want to enlist their help to pollinate your plants, some species will accept human invitations in the form of nesting boxes.
Big, fuzzy, black-and-yellow bumblebees and a few types of small sweat bees are the only native bees that live in colonies. Most other species live alone and associate with others only long enough to mate. Mason bees, carpenter bees and leafcutter bees are called cavity nesters because they make their nests in the holes of trees, fence posts, firewood, hollow plant stems or handmade bee nesting blocks. More numerous ground-dwelling bees dig tubular burrows no larger than a drinking straw. Bumblebees often make their home in underground burrows vacated by rodents.
Like honeybees, bumblebees are general feeders that visit a broad range of host plants. But many wild bees have restrictive tastes and stick close to the plants they were born to serve. Squash bees, for example, followed early strains of squash as native people moved the crop northward from Central America. Females emerge in early summer and only fly in the morning when squash blossoms are open. In the afternoon, you often can find males curled up asleep in closed squash flowers (yes, bees do sleep). Cane recently worked with the specialist bee that pollinates only rabbiteye blueberries — and that does so with amazing efficiency. The adult life of a specialist bee is quite short, but in only a few weeks, just one of them often out-pollinates 100 honeybees.
Because specialist bees need pollen from specific plants, they tend to stay close to home and forage in smaller plantings, says James Tew of Ohio State University’s Honey Bee Lab. Most native bees pose no problem for plants, though leafcutter bees do harvest rounded leaf pieces from roses, ash trees and several other plants, which they use to build their nests. “The small amount of leaf material taken is a bargain when the pollination activities of leafcutter bees are considered,” Tew says.
Various species of leafcutter bee have been found to be much better pollinators of alfalfa, blueberries, carrots, sunflowers and onions than honeybees. For example, in an enclosed greenhouse where carrots were being grown for seed, researchers found that 150 leafcutter bees could do the work of 3,000 honeybees. One non-native species, the alfalfa leafcutter bee, is now reared by the millions because it does such an outstanding job pollinating alfalfa grown for seed.
Particular characteristics contribute to native bees’ pollination talents. Many native bees are quite hairy, and tufts of hair (such as those on the abdomens of female leafcutter bees) serve as soft brushes that gently transfer pollen from a flower’s stamens to its stigma (the female part that connects to the ovary). The buzz factor also is important because some flowers, such as blueberries and most members of the tomato family, need to be vibrated to shake the pollen loose from the stamens. Scientists call this process “sonication,” but Arizona entomologist Stephen Buchmann (co-author of The Forgotten Pollinators) came up with another phrase: “buzz pollination.” Bumblebees, digger bees and several other native bees are great buzz pollinators.
The diversity of native bees matches the diversity of native plants. With the help of his camera, David Gordon, a professor of zoology at Pittsburg State University in Kansas, has seen that some native bees have long tongues, so they can lap nectar from tubular flowers while others have shorter tongues more suited to flat blossoms. Native bees also vary in size from half-inch iridescent sweat bees to 1½-inch carpenter bees. Tiny bees can access the littlest flowers for pollination purposes while bigger bees buzz blossoms, tramping pollen from place to place with their feet, and sometimes accidentally improving pollination by chasing honeybees across the faces of sunflowers and other big-blossomed plants.
Native bees seldom travel more than a quarter mile from their nests, so improving bee habitat can have a very direct benefit in your garden. The Xerces Society, a nonprofit insect preservation group based in Portland, Ore., suggests several simple ways to make your property more hospitable to native bees:
Minimize the use of pesticides and avoid
spraying botanical or biological insecticides in the
morning, when native bees are most active.
Grow a diverse selection of flowering plants (including as many native species as possible).
Grow crops such as squash, sunflowers, blueberries and strawberries every year to maintain resident populations of the specialist bees that serve them.
Leave some areas uncultivated so you don’t disturb bees that nest in the ground.
The same plants that attract butterflies and beneficial insects often attract native bees; both insect groups are most numerous where plants bloom over a long season. For example, early spring-blooming willows and redbuds can be followed by fruit trees, brambles and red clover before your summer vegetables and flowers take over as primary host plants. Then keep the pollen flowing into fall by growing late-blooming asters and allowing goldenrod to flourish along fence rows.
With a solid food supply nailed down, you can further encourage native bees by providing attractive nesting sites. For ground-nesting bees, a patch of uncultivated, well-drained soil that gets morning sun will work well as long as you avoid disturbing it with vehicles and tractors. You also can make a sand pile or sand pit — or simply fill a planter with sand and place it on a warm, south-facing slope. If you see bumblebees buzzing around the roots of a tree, leave them alone. They probably have established a colony in a burrow vacated by mice or voles.
Beyond the benefits of improved crop pollination, good food and habitat for native bees has a ripple effect in the natural world. Native bees pollinate forest trees and wildflowers, which in turn provide food for wildlife. Cane says that because wild bees are vegetarians, they will never ruin your barbeque by buzzing around your burgers. “Sit down and enjoy the bees,” he suggests. “They are great fun to watch.”
Barbara Pleasant is a veteran MOTHER EARTH NEWS contributing editor and award-winning book author. She lives in the mountains of western North Carolina.