University of Maryland Extension

Pollinator Basics

Butterfly caterpillars can consume a lot of foliage in this stage,
but they make up for it with their beauty and pollination
services when they transform into adults.
Video: Dr. Mike Raupp, UMD Entomologist 

Key Points

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 almost all fruits, vegetables, and grains, 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 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, or animals with spines such as bats, birds, and lizards to name a few are plant pollinators. Since so much of the food we eat each day requires pollination, we are indebted to the myriad creatures that perform this critical service.

  pollination illustration
Cross-pollination is the transfer of pollen from one plant to another, 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 limbs 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 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 Pollinators

  • It is important to recognize pollinators at each stage to help preserve them in your garden. It is a good practice to allow some insect larvae 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.
  • 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).
  • All insect pollinators undergo complete metamorphosis: egg, larva (caterpillar, grub, or maggot), pupa, and winged adult.
  • The appearance from one stage to the next changes dramatically, and it is important to recognize pollinators at each stage to help preserve them in your garden (even though caterpillars eat the leaves of plants).

    monarch butterfly life cycle illustration

    Figure provided by Arizona State University at 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.

What are Some 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 even family pets 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 8 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.

What is Threatening 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 and fragmentation: 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 planting only a few species of plants 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

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