By now, every gardener is aware – and hopefully non-gardeners too – that bees are essential for pollinating flowers and other plants, including many food crops. Besides bees, plants are also pollinated by wind, gravity, water, flies, butterflies, birds, bats, moths, beetles, and wasps. Here, we’ll focus on insects and bees and the flowers that attract them (native trees and shrubs are also sources of pollen and nectar for pollinators).
How are plants pollinated by insects and bees?
During a plant’s reproductive phase, a pollinator rubs against the pollen-rich male part of a flower called the anther. The pollinator carries the pollen on its body within the same flower or to a nearby flower of the same species. There it rubs against the female part of the flower, known as the stigma. This fertilizes the flower, which later produces fruit and seeds. Without robust colonies of pollinators – and especially bees who outwork every other pollinator – we’d see far fewer flowers in spring and summer and have far less food to eat. In fact, one-third of all our food is the direct result of pollination by insects.
When does pollination occur?
Pollination occurs during spring, summer, and fall. Plants evolved with differing flower times, so they require pollination at different times of the year. Pollinators evolved alongside these plants over millennia, so they rely on a wide variety of blooms in your garden year-round for their food. Some bees and insects have even developed specific body shapes and traits to pollinate certain flowers.
While pollination doesn’t typically occur in winter, many species of pollinators overwinter in your garden. Don’t be in a rush to clear decaying plants in the fall, as they provide habitat for pollinators during winter.
In a single day, one worker bee makes 12 or more trips from the hive, visiting several thousand flowers. On these foraging trips, the bee can travel as far as two to five miles from the hive. Although honey bees collect pollen from a variety of flowers, a bee limits itself to one plant species per trip, gathering one kind of pollen.
Helping Agriculture’s Helpful Honey Bees, US Food and Drug Adminisration
7 facts about bees:
- Native bees pollinate 80 percent of flowering plants worldwide.
- Honeybees are key to the pollination of certain agricultural plants like almonds and lemons.
- Some native bees only visit the specific plants they have evolved with.
- Many native bees are solitary bees, meaning they don’t live in a hive. They nest in the ground or cavities in trees or rocks.
- Some bees use only one or a small number of plant species for food.
- There are more than 20,000 known species of bees worldwide and 4,000 are native to the U.S.
- Some bees are smaller than a grain of rice and some are as long as 1.5 inches.
Why bees are important
Bees are considered the most important pollinators because they are uniquely adapted to gather and transport pollen. Bees rely on flowers for food to feed their young, so they actively seek out and visit flowers… Bees also forage for food close to their nesting sites, a practice called central place foraging. Bees visit one or only a few flowering species during each foraging trip, even when other flowers are available. This behavior, called flower fidelity or flower constancy, makes bees especially reliable couriers to move pollen to receptive flowers.
Ohio State University Extension, Attracting Pollinators to the Garden
All native bees are plant pollinators. Honey bees, native to Europe, are essential pollinators and are arguably the most important, especially for food crops. They actively seek flowers with pollen, unlike other pollinators who are only interested in the flower’s nectar.
Bees store pollen in their hive – it’s their primary source of protein that provides them with many nutrients. Pollen is also necessary for hive growth and young bee development. Bees also harvest flower nectar and convert it to honey, their primary source of carbohydrates (sugar) for energy. Many bees make honey, but only honeybees make enough for humans to use.
How bees are threatened
Honeybees, bumblebees, and many native bee populations are disappearing. Some estimates put the decline at as many as 23% of native species. One of the greatest threats to bumblebees and native bees is a class of pesticides known as neonicotinoids. These pesticides sometimes kill bees directly, decrease their ability to fight infections or find food, and interfere with their reproductive cycle. Bees exposed to “neonics” become weak and disoriented and have problems finding flowers and returning to their nests. When they feed on plants treated with neonicotinoids, bees end up feeding pesticide-laden pollen to their young, increasing the speed of decline.
Also contributing to the decline of bees is a loss of habitat. Agriculture and land development alters the landscape substantially. For pollinators that are “habitat-specific” (meaning they only nest in one area), the loss of sites for foraging, nesting, and overwintering can be detrimental.
Habitat quality is a contributor as well. While developed land areas may offer many trees and flowers to feed on, the loose soil required for ground-nesting bees may be hard-packed by heavy foot traffic or off-road vehicles or paved over with concrete.
Adding to the habitat quality problem is a lack of connected habitats. Pollinator habitats must be connected so that migratory pollinators can move between them (see Professor Doug Tallamy’s book, Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard). Suppose a large habitat (like a forest) is broken up by highways, buildings, roads, and other development. Now the habitat is broken into many smaller habitats that aren’t connected. This leaves weaker pollinators unable to travel to adjoining habitats, and many will die.
Note: Keeping a beehive is a great hobby, but is not a way to conserve bees. A beehive is home only to European honeybees, not native bees that must live and feed in your local habitat.
How to encourage native bees and pollinators
Many native bees nest in soil, holes in wood (which they may or may not have drilled themselves), or inside certain plant stems. To encourage their nesting, don’t use landscape fabric in your gardens or cover every square inch with mulch. Leave some bare areas in your garden soil and, if possible, your lawn, especially along wood lines or near the bases of shrubs. This encourages nesting for native bees and a safe place to lay eggs. Also, let some dandelions grow in your lawn (you won’t be shamed by your neighbors). Native bees and honeybees use dandelions as an early-season food source, as well as dead nettle, ground ivy, and violets. And never spray plants in flower with insecticides or pesticides.
Which flowers attract bees?
Bees require sugar (flower nectar) to fly. They visit many varieties of flowers to get nectar, but prefer certain species, most often those that are native to your area. To preserve bee and pollinator habitat, plant native flowers, shrubs, and trees in your landscape. For a list of native plants that support pollinators in your area, see the lists from the Xerces Society here.
[table id=19 /]Sources:
University of Florida Gardening Solutions, Perfect Plants for Pollinators; University of Connecticut Home & Garden Education Center; Missouri Botanical Garden, Native Plants to Attract Bees and Native Pollinators; Michigan State University Extension, Bee-friendly plants and pest management strategies – Part 1; U.S. Food & Drug Administration: Helping Agriculture’s Helpful Honey Bees.