While many people understand that native plants are important, there’s often a large gap in understanding which pollinators rely on them. So understanding how to attract, observe, and identify these essential insects is vital to our role in helping them survive and promote biological diversity within the species. To discuss the importance of bees, wasps, and other essential pollinating insects to native plants, and what gardeners can do to support them, my guest this week is biologist, pollinator conservationist and award-winning author Heather Holm.
Heather grew up in Canada and now lives in Minnesota. She had an interest in plants more than insects for many years and studied horticulture and biology. Later in life, she practiced ecological horticulture and worked on ecological restorations. She was amazed by the diversity of insects that her native plant landscapes attracted. The experience inspired her to write her first book, “Pollinators of Native Plants: Attract, Observe and Identify Pollinators and Beneficial Insects with Native Plants.”
To research the book, Heather observed the insects that frequented the flowering plants in her home garden and elsewhere. She knew that it wasn’t just happenstance that the same species of pollinators kept visiting the same species of plants. Getting to the bottom of why sent her down a rabbit hole. “I’ve never really come out of the rabbit hole,” she says.
Heather is now an expert on the mutually beneficial relationship between native plants and native pollinators, the natural history and biology of native bees and predatory wasps in eastern North America, and ecological land stewardship and restoration.
She followed up “Pollinators” with “Bees: An Identification and Native Plant Forage Guide,” which entomologist Doug Tallamy calls the best resource on specialized plants and how they support native pollinators. This year, Heather published “Wasps: Their Biology, Diversity, and Role as Beneficial Insects and Pollinators of Native Plants,” a National Indie Excellence Award Winner in the Nature category. I am so glad I have this book; it is really well done.
Heather says that she and others engaged in similar work often encourage others to slow down and observe the natural environment around them. “I often tell people in my presentations, just sit in one place in your garden for five minutes and you’ll be really amazed what you see because we never do that,” she says.
Before proceeding any further, I want to remind you that I have a new free resource available to listeners of “The joegardener Show.” I created a quick and handy guide on what to plant in your garden to support butterfly populations. Download Attract Common Butterflies with Host Plants and keep it for your reference when choosing plants.
The Reasons for Pollinator Population Decline
Pollinators are any organisms that visit flowering plants and effectively move pollen around from flower to flower of the same species. Bees and butterflies are often what we think of when we think of pollinators, but certain wasps, beetles, true bugs and flies all pollinate. “You’re going to get the whole suite of unusual suspects if you look closely,” Heather says.
During the growing season, Heather frequently posts photos of the pollinators she finds. She goes out for hours on end just looking for pollinators, but the insects are not as abundant as one would expect. Contributing to pollinator decline in Minnesota is climate change: spring comes earlier and warms up faster, and fall is dragged out, with native plants holding leaves longer than they normally would.
Though insect population decline is troubling, Heather looks at the glass as half full: “We have all of these amazing opportunities for people to put more habitat in to support these pollinators.”
In addition to climate change, habitat loss and pesticide use play major roles in pollinator loss. Some adaptable species are increasing in abundance and expanding their ranges, Heather points out, but for many species, that’s not the case.
The Importance of Wild Pollinators
An oft-quoted statistic states that one-third of all of the food we eat is thanks to honeybees — though there are no native honeybees in the United States. The honeybees here were imported from Europe.
According to the U.S. Department of Agriculture Natural Resources Conservation Service, three-fourths of the world’s flowering plants and about 35 percent of the world’s food crops depend on animal pollinators to reproduce. Our native bees are doing a lot of the pollination for agriculture and home gardens and are more important than they are given credit for.
Heather says the diversity of wild bees in North America has been largely ignored until recently. A change in priorities came when colony collapse disorder began affecting honeybees and threatening the agriculture industry. Attention turned to alternatives that could fill the void, namely, wild bees.
The Special Relationship Between Native Bees & Native Plants
Native plants and native bees co-evolved to serve each other’s needs. In the Eastern United States, about one quarter to one third of native bee species are actually specialists of native plants, Heather points out. Without those specific native plants in our landscapes, we won’t have those bees to aid in the pollination of our food crops.
Some native bee host plants are also butterfly host plants, making them real powerhouse plants in terms of supporting pollinators. Not only do these plants provide nutritious pollen for a specialist bee, but their leaves are consumed by and butterfly caterpillars.
Common Groups of Native Bees
Native bees come in a variety of sizes, from as small as a grain of rice to the large carpenter bees found on the East Coast. Heather says gardeners have many different opportunities and habitats for bees: in-ground, above ground, in cavities, in stems, etc.
Bumblebees (Bombus) are the most familiar native bees. There are more than 20 species of bumblebees in the Eastern United States, Heather notes. Though most native bees are solitary creatures, bumblebees are social bees with small, annual colonies.
Carpenter bees (Xylocopa) are native pollinators that are not always welcome because they drill holes in barns, fences and any other wood they can find. However, I am willing to make sacrifices because of the important work carpenters do as pollinators. Heather says carpenter bees are the only destructive nesters. Other native bees that nest above ground look for existing cavities rather than making their own.
Mason bees (Osmia) belong to a family of bees in which the females collect pollen on the bottom of their abdomens. Mason bees are particularly of interest to growers of fruit trees because they are out pollinating in early spring. They are so named because they collect mud to build their nests.
Leaf-cutter bees (Megachile) cut semicircles out of leaves and petals to build their nests. They are in the same family (Megachilidae) as mason bees.
Sweat bees (Halictidae family) are mostly ground-nesting. They are called sweat bees because they are attracted to perspiration.
Yellow-face bees (Hylaeus) are pretty much hairless and don’t look like bees at all. They are super tiny and nest in little stem cavities.
Habitat Diversity of Native Bees
Native bees can be picky about where they will nest. For example, of the 70% of bees that nest in the ground, some will only nest in compacted bare sand. Others will nest in heavy clay and collect water to make the nest excavation easier. The soil pile around excavated nests is called the tumulose. Look for the tumulose to tell the difference between an ant colony and a bee nest.
Of the remaining 30 percent of bees that nest aboveground, some nest in holes in wood, such as cavities in a standing dead tree. Others prefer to nest in a dry-rotting log on the ground, and still others prefer to nest in hollow or pith-filled stems. By leaving dead trees standing, leaving fallen trees to rot and refraining from cutting stems short, we can offer native bees nesting opportunities on the land that we steward. “Stem stubble,” as Heather calls it, is valuable real estate for bees.
Why Commercial Bee Hotels Are Problematic
There are commercially sold bee hotels to provide nesting sites for mason bees, grass-carrying wasps and other beneficial insects. Heather compares these bee hotels to birdhouses: You wouldn’t put up a birdhouse and never go back and maintain it. Birdhouses and bee hotels need maintenance to provide desirable, sanitary conditions for wildlife.
Many bee hotels are of poor design with bamboo stems that are too short for bees. Bees want a lengthy cavity in which they deposit pollen and nectar at the back, lay a single egg, make a partition and repeat. Short stems make the bee larvae more vulnerable to woodpeckers, parasitoids and other threats. Bee hotels also put many bees in very close proximity, which doesn’t happen in nature. That proximity makes it easy for pathogens to spread from one cavity to the next.
Paper straws are better than fixed bamboo stems. The paper straws can be easily pulled out and replaced every two years. This reduces the waste and pathogens in the bee hotel. The bamboo stems are also bigger in diameter than tiny and medium bees prefer.
What to Know About Wasps
Wasps often get a bad rap as nothing more than stinging insects, but there is such variety among wasp species and many important roles that wasps play.
While bees are vegetarians, wasps are carnivorous. Adult wasps hunt insects and spiders that they take back to their nests to feed their broods. The adults themselves have a vegetarian diet of sugary substances such as nectar, tree sap or honeydew. When they go after nectar, they incidentally pick up pollen on their bodies and pass it between flowers.
As predatory insects, wasps control the populations of other insects, including pests that destroy crops. For example, braconid wasps lay their eggs in tomato hornworms, killing the hornworms before they can destroy tomato plants.
Moths and Pollination
Another often overlooked pollinator is the moth. Moths are nocturnal and pollinate at night when we can’t see and appreciate them. Little is understood about nocturnal pollination but more research is being done. Heather got herself a flashlight that shines red so she can look for moths in her garden at night. Most flower-visiting insects are red blind, Heather explains, so they won’t be scared off by the red light.
Provide Blooms From Spring Through Fall
Because of the wide variety of pollinator species and their different periods of activity from one species to the next, it’s important that your garden has flowers in bloom from early spring all the way through late fall. Species that are active for a narrow period of time won’t make a home in your garden if your garden is not in bloom when their adults are out and nesting.
Bees need both nectar and pollen, and not every flower species produces nectar. On the other hand, some produce very little pollen, and pollen is the protein source that bees feed their offspring. To fuel the activities of pollinators, many species of flowers are needed.
Plants in the aster family (Asteraceae) are powerhouses that support the most specialist bees, Heather says. They generally bloom in the summer and fall months, they are big pollen produces and their nectar is easily reachable. Goldenrods (Solidago) are also fantastic fall-blooming plants. You can have multiple species of both asters and goldenrods in your garden to serve numerous species of bees.
Dogwoods, willows, blueberries and redbuds are all great plant choices to support pollinators in fall. Redbuds support specialists and leaf-cutter bees love redbud leaves.
Spring-blooming woodland plants followed by spring-flowering shrubs are important for pollinators in the Eastern United States. Woody plants and trees, such as buckeye and tulip poplar, do a lot of the pollen and nectar offering in spring, Heather says.
Another consideration is the type of environment. A prairie needs different plants than a woodland or wetland edge. Another way to say this is to put the right plant in the right place. Be conscious of your regional ecosystem plant communities and where they thrive.
Floral repetition is also important. It’s not enough to have one plant of each species in your garden. Groupings of multiple pollen-rich plants will attract more pollinators than a single plant, and we gardeners find it more attractive too. Groupings also improve cross-pollination.
Where Bees Spend the Winter
For social bees such as bumblebees and some sweat bees, the females overwinter as adults. They hibernate in an insulated place, such as an abandoned rodent hole or under the duff layer. Most solitary native bees spend the winter in their nests finishing their development from pupae to adults.
Leave the Pesticides on the Shelf
Pesticides are a threat to pollinators and other beneficial insects. “If you’re going to go to all this trouble of providing this wonderful flower buffet for these pollinating insects, why do you want to bring them in and then potentially kill them?” Heather wonders. “We just need to grow more of a tolerance for insect damage and understand that it’s really a small minority of insects that do cause damage to plants, and in many cases don’t actually kill the plant. So if we can build up some tolerance, then it really helps to leave those pesticides on the shelf.”
Native Plants Vs. Nativars
Native plants are straight species, and among the species are many local genotypes that are adapted to your area. Cultivated native plants are called “nativars.” They have been selectively bred for certain traits, but that comes at the expense of genetic diversity. Nativars are vegetatively propagated, which is a form of cloning. They may have a more vibrant flower color or be of a shorter stature.
Heather says nativars are a good substitute if you don’t have a native plant nursery around. “Do the best that you can to have straight species, but cultivars aren’t evil,” she says.
I hope you have a greater appreciation of native bees and wasps after listening to my conversation with Heather Holm. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.
How do you attract pollinators to your garden? Let us know in the comments below.
Links & Resources
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“Bees: An Identification and Native Plant Forage Guide” by Heather Holm
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