The majority of flowering plants evolved to take advantage of insects, and depend on them (and less commonly, other animals or wind) to fertilize their flowers, facilitate gene flow, and prevent inbreeding. Bees might be the most obvious pollinators, and on a warm summer day it seems flowers and bees were made for each other. Native bees, including the 90% of species native to the U.S. that are solitary rather than social — that is, females create nests and raise their young without the help of any other bees — are considered to be the most important pollinators (move over, European honeybees!) and are invaluable members of natural systems. But other capable pollinators—like butterflies and moths, hummingbirds, wasps, ants, herbivorous fruit bats, and even rodents—share the pollen distribution workload, and offer ecological benefits as well. Less well known are the thrips, beetles, mosquitoes (yes, you read that right), and flies that are actually quite accomplished pollinators. Distributing pollen may be a sideline for them, but they often excel because they don’t take pollen back to their nests, as most bees do.
Thrips go way back—to the Permian period, over 250 million years ago—but get a bad rap because of a few species that threaten crops. Studies show that they are strong pollinators of some plants, particularly early in the season when most other pollinators aren’t around.
Beetles are particularly important in semi-arid parts of the world and have a highly developed sense of smell. They are expert and essential pollinators, according to the Forest Service, and also were around millions of years before bees appeared. Like many species of birds, bees, and butterflies, beetles are in danger of extinction. The International Union for Conservation of Nature lists over 70 beetle species as endangered. The main threats include habitat destruction, chemical pollutants (e.g., pesticides), displacement by introduced species, and hybridization with other species due to human interference.
Although many flies (order Diptera) are recorded as flower visitors, relatively little is known about pollination by flies, compared to other more obvious pollinators. Many flies are strong pollinators, including syrphid flies (which deserve their very own special post) as well as some tachinid flies, which are the most diverse family of the order Diptera (true flies). As adults, they are flower visitors, feeding on nectar and/or pollen; in their larval stages many species help to control insects that we consider pests.
While I’m not advocating the nurture of mosquitoes in your garden (the females do suck blood and can carry disease, after all!), it’s noteworthy that mosquitoes, like all insects, do have a role in natural systems. Their primary source of food is flower nectar (with males eating nothing but nectar) and they buzzily and incidentally carry pollen from flower to flower. Plants like goldenrod (Solidago spp.) use mosquitoes as pollinators, as do orchids of northern latitudes, grasses, and many other types of plants. And they are a source of food for birds, fish, amphibians, spiders, bats, dragonfly larvae, and other animals.
How you can help a variety of pollinators
Within our increasingly fragmented landscapes, gardens that provide pollen and nectar-rich plants—as well as nesting and overwintering sites—can create critical habitat and connections for pollinators and other creatures. No space is too small, and when in close proximity to other larger gardens, natural areas, or greenways that sustain native plant populations appropriate to the region, their value deepens.
◊ Choose natives that occur naturally in your area, or at the very least heirloom ornamentals (rather than newer hybrids that may not provide sufficient or appropriate nutrients that native species do). Some garden herbs like cilantro, parsley, and dill attract some pollinators when allowed to flower.
◊ Avoid nonnative invasive species like “butterfly bush” (Buddleia davidii) that sound good, but aren’t.
◊ Provide structure and layering in the form of native trees and shrubs that provide food, cover and nesting sites for various pollinators.
◊ Plan for continuous flowering, spring through fall. Early spring nectar is particularly important for early-emerging queen bumble bees and other solitary bees, as well as flies and beetles.
◊ Choose a variety of plants that differ in the size, shape, and color of blossoms to attract a variety of pollinators. Arrange perennials in drifts or swaths of at least three of a kind, rather than singly here and there. And don’t forget that trees and shrubs produce flowers!
◊ Stay away from pesticides and other chemicals. Insecticides, herbicides, fungicides, and synthetic fertilizers are particularly harmful to sensitive pollinators. Don’t purchase plants pre-treated with neonicotinoids; if you’re unsure, ask.
◊ Don’t be too neat. Leaf litter, dead wood (tree snags or piles of branches), and other natural detritus provide essential habitat, nesting materials, and overwintering sites for adult pollinators or their eggs, larvae, or pupae. And allow some bare soil for pollinators that nest in the ground.
◊ Grow lepidoptera (butterfly and moth) host plants that provide food and habitat for their young. Find out which species frequent your area and grow the native plants that they need to breed.
◊ Provide shallow water and some moist soil. A shallow pie plate or flowerpot saucer, filled with clean gravel or small rocks allow insects to drink without drowning. Also, butterflies and moths need muddy or sandy puddles to obtain water and nutrients. Add a dash of salt to be sure male Lepidoptera get enough sodium prior to mating.
Please see this post for more detailed info on supporting pollinators in all their life stages.