sweat bee on a flower

Sweat bee. Photo: Susan Ellis, Bugwood.org

Updated: March 1, 2023

About pollination and pollinators

  • Pollination is the process by which plants reproduce and create seeds. Animals, called pollinators, are necessary for the movement of pollen from one plant to another.
  • Insect pollinators include bees, wasps, beetles, flies, butterflies, and moths. 
  • Habitat loss and fragmentation (the process of breaking up large pieces of land into smaller more isolated patches), and the use of broad-spectrum pesticides are two of the main threats to insect pollinators.

What is pollination and why is it important?

  • Pollination is the transfer of pollen from the male organ to the female organ of a flowering plant. A majority of plants require pollination to reproduce.
  • Over 90% of all known flowering plants and many fruits and vegetables require pollination to produce crops.
  • Pollination is essential to life on earth, for without it most people and non-human animals would not have enough food. Since one out of every three bites of food we eat each day requires cross-pollination, we are indebted to the myriad creatures that perform this critical service. Over 100,000 species of invertebrates, mostly insects, and over 1,000 species of vertebrates, animals with spines such as bats, birds, and lizards to name a few, are plant pollinators.
illustration of cross-pollination

Cross-pollination is the transfer of pollen of one flower or plant to another flower or plant, often facilitated by invertebrate pollinators such as bees and wasps, butterflies and moths, flies, and beetles.

  • As pollinators feed and fly about the garden, pollen grains stick to their bodies and are rubbed off on female flower parts as the insects go from flower to flower.
  • Pollinators help plants reproduce and in return, flowering plants produce food for pollinators in the form of pollen and nectar, a highly nutritious sweet fluid.
  • Not only do pollinators boost the productivity of crops in this way, but they also help ensure the reproduction and survival of many flowering plants.
  • Learn more about gardening to attract pollinators.

Types of insect pollinators

  • There are four major groups of insect pollinators: bees and wasps, beetles, butterflies and moths, and flies. Some are generalists and visit many flowering plants, and others are specialists that concentrate on a single plant (e.g. yucca moths).
  • European honeybees are the most well-known pollinator species, but Maryland is home to at least 400 species of native bees that are essential to plant reproduction and food production. Learn more about honeybees: University of MD Honey Bee Lab and native bees US Geological Service Native Bee Inventory and Monitoring Lab.
  • All insect pollinators undergo complete metamorphosis: egg, larva (caterpillar, grub, or maggot), pupa, and winged adult. Illustrated in figure below.
  • It is important to recognize pollinators at each life stage to help preserve them in your garden. Their appearance from one stage to the next changes dramatically. It is a good practice to allow the larvae (caterpillars) of some pollinators to feed in your garden by providing them with their preferred host plant.
  • Many caterpillars are picky eaters and eat only certain plants! For example, the monarch caterpillar feeds on milkweed, so providing this valuable food resource ensures the adult butterfly will survive.
Monarch lifecycle

Insect pollinators undergo complete metamorphosis, which includes four distinct life stages: egg, larva, pupa, and adult. This diagram shows the life cycle of the monarch butterfly starting from a tiny egg and working counterclockwise to adult. Figure provided by Arizona State University at https://askabiologist.asu.edu/monarch-life-cycle

Other kinds of pollinators

  • Pollinators come in many shapes and sizes. While insects make up a vast majority of pollinators, vertebrates, such as bats, hummingbirds, and mammals roaming through your garden, may also act as important pollinators.
  • Bats don’t see well but have a keen sense of smell; they forage at night and are attracted to large, white, or pale night-blooming flowers with strong, fruity scents. Pollen dusts their foreheads as they feed on nectar by thrusting their long tongues deep into blossoms, and this pollen is transferred to the next flower visited.
  • Hummingbirds love vivid colors, such as red, purple/red, orange, and pink, but are not particularly drawn to fragrances. These mighty little birds will feed up to 10-12 times an hour and are important pollinators of brightly colored, tubular-shaped flowers. They are often seen hovering before and feeding on sages, fuchsias, honeysuckles, nasturtiums, columbines, jewelweeds, and bee balms.

Threats to pollinators

Any practice that potentially creates an imbalance in the natural ecosystem may impact the pollinator biodiversity on which much food production depends. Of particular concern are:

  • Habitat loss: Pollinators need a variety of native flowering plants in addition to introduced flowers to provide nutrition specific to their needs, as well as adequate food supplies throughout the growing season. Land development, elimination of native flowers and weeds, and limited plant diversity in yards and landscapes reduces resources and suitable nesting sites for pollinators, leading to reduced pollinator populations.
  • Fragmentation of habitats increases the distance migratory pollinators must travel between areas providing food and shelter along their routes, adversely impacting survival for insects such as monarch butterflies.
  • Pesticides: Broad-spectrum pesticides are a major threat to pollinators, both directly from unintentional poisonings, and indirectly from habitat reduction when native forage plants are destroyed with herbicides.

Additional resources

Compiled by Chris Sargent, University of Maryland. Rev. 2020 by Margaret Hartman, M.S. student, Department of Entomology, University of Maryland