Native Pollinators

Matthew Shepherd & Mace Vaughan, The Xerces Society

“The conservation biology issues are not simply esoteric concerns relevant only to middle-class bird-watchers and bug-netters. These issues should strike a chord in every person who cares about where our food comes from and whether it is wholesome to eat.” — Stephen L. Buchmann and Gary Nabhan, The Forgotten Pollinators

Pollinators are among the hardest working creatures of the natural world. Pollination, the transfer of pollen grains from the anther to the stigma of the same or another flower, is necessary for plants to produce seeds and fruit. Up to 80 percent of the world’s flowering plants rely on animals – pollinators – for this transfer. Insects pollinate two thirds of the world’s crop species, whose fruits and seeds together provide 15 to 30 percent of the foods and beverages that we consume-approximately one out of every four mouthfuls.

• The United States alone grows more than one hundred crop plants that need pollinators, such as apples, cherries, pumpkins, blueberries, and many other fruits and vegetables filling grocery store shelves.

• Insect-pollinated crops contributed an estimated $20 billion to the United States economy in 2000. If this calculation is expanded to include indirect products, such as the milk and beef from cattle fed on alfalfa, pollinators may be responsible for almost $40 billion worth of agricultural products each year.

The work of pollinators has value beyond the clearly economic. Pollinators are keystone species in most terrestrial ecosystems, that is, species upon which the persistence of a large number of other species depends. They are essential to the reproductive cycles of most flowering plants, and thus to the ecosystem itself. Fruits and seeds are a major part of the diet of approximately 25 percent of birds and many mammals, ranging from the American goldfinch to the grizzly bear. In some areas, these pollinator-supported plant communities bind the soil, thereby preventing erosion, conserving an important agricultural resource, and keeping creeks clean for aquatic life.

Despite its importance, in many places the essential service of pollination is at risk. There is a growing body of evidence that the loss, alteration, and fragmentation of habitats and the extensive use of pesticides have contributed to a decline in pollinator populations and reduced fruit set, a trend that has been recorded on all continents. However, landscape change does not always result in negative impacts. Wooden structures such as buildings and fences and partially compacted soils on roadsides have unwittingly provided nesting sites for solitary bees. Flowers in gardens and parks offer foraging that some bees can exploit. Nevertheless, there is reason to be concerned. We should be acting now to protect our forgotten pollinators.

Pollinator conservation is an easy and straightforward thing to do. It needs little or no specialized knowledge or equipment and can be done in any situation. Whether you are a homeowner working in your own garden, a land manager for a city park, a farmer with field margins, or a steward for a nature preserve, there is something you can do to help pollinators. Providing patches of flowers is one thing we all can do to improve our environment for pollinators. And, creating foraging habitat not only helps bees (and other pollinators) but also results in a beautiful, appealing landscape.

Like all wildlife, pollinators need food and shelter, which you can provide by:

• Growing a diversity of native plants whose blooming times overlap to provide flowers throughout the seasons.

• Maintaining a landscape free of poisonous pesticides.

• Establishing nesting and egg-laying sites, with appropriate nesting materials.

• Constructing sheltered, undisturbed places for hibernation and overwintering.

This article focuses on plant selection, but undisturbed nests and overwintering areas are crucial for population survival. For excellent nest and shelter ideas, visit the Xerces Society’s web site, www.xerces.org, or read their Pollinator Conservation Handbook.

Choosing the Right Flowers

To help bees and other pollinator insects–such as butterflies–you should provide a range of plants that will offer a succession of flowers, and thus pollen and nectar, through the whole growing season. Patches of foraging habitat can be created in many different locations, from backyards and school grounds to golf courses and city parks. Even a small area planted with good flowers will be beneficial for local bees, because each patch will add to the mosaic of habitat available to bees and other pollinators.

Use local native plants. Native plants, which are usually best for native bees, can be used in both wild areas and gardens. Research suggests native plants are up to four times more attractive to native bees than exotic (nonnative) flowers. Native plants are also usually well adapted to your growing conditions and can thrive with minimum attention.

Use heirloom varieties. For the garden, heirloom varieties of herbs and perennials are good sources of nectar or pollen and thus provide good foraging. Having garden and native plants will make a garden attractive to both pollinators and people.

Chose several colors of flowers. Bees have good color vision to help them find flowers and the nectar and pollen they offer. Flower colors that particularly attract bees are blue, purple, violet, white, and yellow.

Plant flowers in clumps. Flowers clustered into clumps of one species will attract more pollinators than will individual plants scattered through the habitat patch. Where space allows, make the clumps four feet or more in diameter.

Include flowers of different shapes. There are nearly one thousand different species of bees in the Pacific Northwest, and they are all different sizes, have different tongue lengths, and will feed on different shaped flowers. Therefore, providing a range of flower shapes means more bees can benefit.

Have a diversity of plants flowering all season. Most bee species are generalists, feeding on a range of plants through their life cycle. By having several plant species flowering at once and a sequence of plants flowering through spring, summer, and fall, you will support a range of bee species that fly at different times of the year.

Suggested Native Plants

Native plants should be your first choice to help our native bees.  This list is not exhaustive; many other native plants are good for bees.

Aster Aster
Bee balm Monarda
Black-eyed Susan Rudbeckia
Ceanothus Ceanothus
Chokecherry Prunus
Coneflower Echinacea and Rudbeckia
Cow parsnip Heracleum
Currant Ribes
Elder Sambucus
Fireweed Chamerion (Epilobium)
Fleabane Erigeron
Goldenrod Solidago
Hawthorn Crataegus
Huckleberry Vaccinium
Larkspur Delphinum
Lupine Lupinus
Madrone Arbutus
Milkweed Asclepias
Mint Mentha
Oregon grape Berberis (Mahonia)
Pacific waterleaf Hydrophyllum
Pearly everlasting Anaphalis
Penstemon Penstemon
Phacelia Phacelia
Rabbit-brush Chrysothamnus
Rhododendron Rhododendron
Roses Rosa
Salmonberry Rubus
Saskatoon Amelanchier
Snowberry Symphoricarpos
Spirea Spirea
Stonecrop Sedum
Wild buckwheat Eriogonum
Wild onions Allium
Willow Salix
Yarrow Achillea

Non-native Garden Plants. Flower beds in gardens, business campuses, and parks are great places to have bee-friendly plants. Many garden plants can be used as a supplement to native plants in landscaping. See information at www.xerces.org for good non-native pollinator plants.

Plants also provide other resources beyond food for many insects, and many insects require different things at different life stages. For example, a butterfly begins as an egg, hatches into a wriggling, crawling caterpillar that bites and chews on plants, has a period of inactivity as a chrysalis, and then emerges as a flying adult that can only drink fluids. Providing for these means more than just flowers for nectar and pollen.

Caterpillar host plants. The caterpillars of each butterfly species have their own limited menu of plants upon which they will dine. Female butterflies lay their eggs on or near these host plants and will only be able to lay eggs if there are the right plants. To start with, grow host plants for the more common butterflies you already see flying through your property and then branch out as you learn more.

Some host plants and the larvae they feed

Desert parsley (Lomatium spp.), Swallowtails
Cow parsnip (Heracleum spp.), Swallowtails
Milk vetch (Astragalus spp.), various Blues
Lupines (Lupinus spp.), various Blues
Clover (Trifolium spp.), Sulfurs and Blues
Milkweed (Asclepias spp.), Monarch
Thistle (Cirsium spp.), Painted lady
Violets (Viola spp.), various Fritillaries
Vetch (Vicia spp.), Sulphurs and Blues
Winter cress (Barbarea spp.), Orange tips
Willow (Salix spp.), many species
Aspen (Populus spp.), many species
Snowberry (Symphocarpus spp.), Sphinx moths
Rose (Rosa gymnocarpa), Mourning cloak
Spirea (Spirea spp.), many species
Grasses and sedges, many species

Hiding places for butterfly pupae. After several weeks of eating and growing, caterpillars need to transform (pupate) into their adult, winged forms. They do this within the protection of a chrysalis. Before becoming a chrysalis, however, a caterpillar wanders in search of a protected site. Depending upon the species, this safe haven could be a bush, tall grass, or piles of leaves or sticks.

Overwintering sites. Depending upon the species, butterflies may overwinter (hibernate) as eggs, larvae, pupae, or even adults. You might find them on plants, under leaf litter, under loose bark, or in piles of logs and other debris. To help these hibernators, a little untidiness goes a long way. Two or three weeks before the severe cold of winter sets in, clean up a minimum of leaves and garden debris and create a pile of logs or leaves.

Pollinator insects form a hugely diverse group of animals. Bees, butterflies, moths, flies, and beetles are just the major groups, and the needs of these are not all met by providing plants. Fortunately, there are some other things you can do that will benefit a large number of these. Here are a few hints.

Fruit and sap. Adult butterflies need sugar to fuel their search for mates and egg-laying sites. Nectar provides most of this but some butterflies, such as the mourning cloak, get sugars from rotten fruit or the sap leaking from wounded trees. Plates of rotting fruit (such as peaches, melons, or bananas) will attract many of these beautiful insects.

Minerals and salt. Because plants contain very little minerals or salt, many adult butterflies need to find another source of these nutrients. In the wild, they can get these by tasting exposed clay deposits, animal urine, saliva, or even bird droppings. They also will come to mud puddles that you create. Scrape a small depression in the ground, line the edges with pebbles, and add some water each morning. It is best if these puddles dry out by the end of each day.

Plenty of sun and protection from the wind. Adult butterflies need to be warm in order to fly. Therefore, nectar flowers and larval host plants should be grown in an open, sunny area protected from the wind by large shrubs, a hedgerow, a fence, or some other windbreak. You could also put out large, flat rocks placed in the sun. These rocks will soak up the sun’s heat and give the adult butterflies a place to warm themselves.

Bee nest sites. The great majority of bees are solitary nesting species that create nests in beetle-riddled snags or dug in the ground. The bees may remain in the nest for a year or more as they pass through the egg, larva, and pupa stages. Wooden blocks drilled with small holes or patches of bare ground can provide secure nest sites.

No insecticides around house or garden. Please don’t use pesticides. Alternative methods for controlling specific pests without using chemicals are available, but even these should be used with caution, keeping in mind the various life stages of butterflies and other insects.

Remember, anything you do will help. Even just a few plants can provide important food and habitat.

“Taking action now in response to these early alarms might allow North Americans to avert the very real and widespread declines that are now being detected among central European bee faunas.” –Jim Cane and Vince Tepedino (USDA-ARS Bee Biology and Systematics Laboratory)

You’ll also find great advice and information in these books:

The Xerces Society and the Smithsonian Institution.  Butterfly Gardening: Making Summer Magic in Your Backyard. Sierra Club Books, San Francisco, CA.

Buchmann, S. L., and G. P. Nabhan. 1997. The Forgotten Pollinators. Island Press, Washington, D.C.

Shepherd, M., S. L. Buchmann, M. Vaughan, and S. H. Black. 2003.  Pollinator Conservation Handbook. Xerces Society, Portland OR.

Vaughan, M., M. Shepherd, C. Kremen, and S. H. Black. 2004. Farming for Bees: Guidelines for Providing Native Bee Habitat on Farms. The Xerces Society, Portland, OR.

The Xerces Society’s web site, www.xerces.org, has plenty of information and many downloadable factsheets about pollinator conservation.

The Xerces Society for Invertebrate Conservation is a non-profit organization dedicated to protecting invertebrates and their habitat through science-based conservation, education, and advocacy.  For more information, or to make a donation, please see their website:  www.xerces.org

Pollination is only one of many beneficial functions (often called “ecosystem services”) that insects provide. An important link in the food chain, insects are eaten by many species of birds, reptiles, amphibians, fish and mammals, providing a crucial protein source for growing animals. There is a reason fishers tie “flies” to catch fish; restoration efforts focusing on salmon or other fish populations may benefit from considering insect needs in the plant selection process. Various insect species also control “pest” insects through predation or parasitism. Overall, gardens and ecosystems are more healthy and self-sustaining with good populations of diverse insect species. Now is the time to provide for our forgotten pollinators on any land we manage, and not just to assume that “they’ll live somewhere else.”