Everywhere you turn, there’s another blog, another Facebook post, another news article about climate change. Even the climate change deniers have switched to complaining that we don’t know why it’s changing. From the perspective of a landscape designer, this is a major challenge; we don’t know if the plants we’re specifying for that lovely perennial border are going to cope with too much rain, or no rain, or if that community will permit watering in an ongoing drought.
But we’re not the only ones who live here on this changing world, and we really have to take that into account when designing. Many of those other dwellers – most of them insects – have an enormous impact on our landscapes and on our very lives. Did you know that one in three mouthfuls of food or drink is only possible because of pollinators?[i] It matters to us and our clients that the landscapes we’re designing are beautiful, but it’s becoming more apparent that beautiful is not enough. The push for the use of native plants is not just plant snobbery; it’s a recognition that we need all those unseen, unacknowledged neighbors so we can continue to live here.
Unless you like bugs (like me!), pollinating insects are not something you think about every day. We and our clients worry about bugs, but usually only in terms of what damage the bug is doing. If we worry about the health of the bugs, it’s the really visible, friendly insects like bumblebees and butterflies that get the headlines. There are a lot of other native[ii] insects, however, who play a role in the pollination that’s so essential to our well-being, and getting to know them will hopefully lead you to think of the insects, too, when designing landscapes. (You might also be interested to know that only about one percent of all 4 million insect species interact with humans in negative ways[iii], and that studies have shown the overall value provided by the world’s insects to be $57 billion – that’s billion with a B.)
We have grown a lot as a culture. We use Integrated Pest Management (IPM) now instead of indiscriminately tossing around poisons (well, not as much, anyway) – but remember that IPM means controlling pest numbers, not destroying the pest. That’s not just an acknowledgement that we can’t effectively destroy a pest without poisoning ourselves. It’s also an awareness that what is, today, a pest may very well be a pollinator once it grows up. Or it might feed those oh so important pollinators in either their larval or adult forms. And it’s a reflection of the fact that, when we zap all the pests, we often zap the insects that prey on them…and pests multiply far, far more quickly than predators. Use poison, and you might very well end up with a rebound population of pests larger than the one you initially “took care of,” without predators to keep them in check.
There are four major classes of pollinating insects: bees and wasps, flies, butterflies and moths, and beetles. Bees (both native and imported) are considered the most important pollinators, because they deliberately gather pollen and nectar to feed their young, rather than just transferring what they happen to have bumped up against. Honeybees are the bees most people are familiar with, but native bees are far more efficient pollinators than the imported honeybee; they forage over a longer period of daylight, in weather which keeps honeybees in their hives, and they visit many different plants in a given foraging trip, thus increasing the pollination across many species at the same time. One study showed more than twice as many hours’ foraging for blue orchard bees—33 hours—compared to honeybees pollinating in the same area (15 hours). It takes only 250 female orchard bees to pollinate an acre of apples–a task it would take 15,000 honeybees to accomplish![iv] Bumblebees are often the first bees active in the spring and the last still active in the fall. Bumblebees also have the ability to “buzz-pollinate,” vibrating their bodies to shake pollen from the plant’s anthers. That’s what they’re doing when you hear them making a racket down inside a flower!
There are about 500 species of native bees in Virginia, including about eighteen species of bumblebees. Most are solitary bees; they do not form colonies, which gives the added advantage (to us!) that, lacking a colony to defend, they tend to be far less aggressive than honeybees. Instead, they nest in the ground, in bunchgrass clumps and brush piles, or inside woody stems of plants. Bumblebees also favor abandoned mouse burrows. Not all types of soil are favored by the ground dwellers. If you happen to find an area of the sandy, south-facing soil they like, and there are bees nesting there, do your best to conserve the area as it is; any sort of deep disturbance of the soil can destroy the bees’ nests before they can reproduce.
The area covered by an individual bee depends largely on its size. Large carpenter bees and bumblebees can travel a mile or more from their nest. Mining bees and leafcutter bees might forage 400-500 yards out. Small bees like the sweat bees[v] and the smaller carpenter bees only go about 300 yards. The tiniest bees might be limited to no more than a couple hundred feet.
Wasps[vi] are relatively weak pollinators, lacking both body hair and the long tongues possessed by bees, but they do carry grains of pollen from plant to plant as the adults feed on nectar or hunt other insects to feed their young. Wasps’ real value to the gardener is as a predator of pest insects from aphids to cicadas.
Flies[vii], members of one of the largest insect orders on Earth, are the most frequent visitors to flowers. They are often important pollinators for specific plants, including some human food plants (strawberries, onions, and carrots, yum!). Lacking a sting, many flies mimic bees or wasps in their shape and coloration. To tell them apart, remember that flies have one pair of wings (bees and wasps have two) and shorter, clubbed or down-turned antennae; bees’ and wasps’ antennae are longer and uniformly shaped.
Most flies we see are syrphid flies, though we may also encounter bee flies and tachinid flies. Their mouthparts are short, limiting them to the disk-shaped flowers (e.g., Queen Anne’s Lace, the wild relative of the carrot). Many flies are predators of other insect species.
Butterflies and moths, even more than bees, are the insects most people recognize and, while they are not the most important pollinator, they are certainly the most conspicuous and one of the reasons most often cited for wanting a native plant garden. Their pollinating is by virtue of brushing up against the pollen-bearing anthers while they sip nectar with their long, long tongues.
Moths, the less visible of the two, are actually represented in much larger number—more than 10,000 species in North America compared to about 800 for butterflies—and are far more important as pollinators, especially for plants which bloom at night. You may very likely have seen a large, hovering shape sipping at coneflowers and thought it was a hummingbird, only to realize it was a moth—a hummingbird moth!
Beetles, our final category of native pollinators, comprise the greatest diversity of pollinators with nearly 30,000 species in North America alone (and more than 340,000 worldwide). Because they are an ancient creature and very likely the first insect pollinators of prehistoric flowering plants, they are adapted to flowers which still retain their ancient, open bowl characteristics, like magnolias and water lilies. Flowers which are pollinated by beetles often give off a characteristic odor to attract them. In addition to their pollinating duties, beetles are important because their larvae burrow tunnels in decaying wood which wood-nesting bees later use. One of my favorite beetles, the soldier beetle, looks a lot like a firefly. Other important (for our purposes) families of beetles include the long-horned beetle with hugely elongated antennae; jewel beetles, whose bodies are amongst the most brightly colored in the insect world; scarab beetles, including one of the most important pollinators of native magnolias, the flower scarab; and blister beetles, whose name is very apt if you’ve ever tried to pluck the adults off tomato plants. As adults, many of the beetles listed above feed on nectar and pollen, and in doing so, promote pollination. They’re also great predators of other insects, including pest species. Blister beetle larvae hitch rides on foraging bees, returning with the bee to the bee’s nest, where they then feed on bee larvae; their numbers are an indicator, therefore, of the relative health of the local bee population.
Want to know more about what these various insects look like, or how to identify them in the wild? Check out the Xerces Society, dedicated to the preservation of invertebrate species, at www.xerces.org. Various Xerces Society publications formed much of the basis for this article, including their book, Attracting Native Pollinators. There are also a lot of great photos of pollinators at http://www.restoringthelandscape.com/p/insects.html.
[ii] I’m focusing on native pollinators here because, in fact, there are more of them and they’re far more effective pollinators than the imported, and beleaguered, honeybee. Honeybees are important…but it’s the native pollinators that are going to save our stomachs.
[iii] Doug Tallamy, Bringing Nature Home, p. 109.
[iv] “Native Pollinators on the Farm: What’s In It for Growers,” fact sheet produced by Xerces Society.
[v] See http://www.restoringthelandscape.com/2012/12/native-bee-spotlight-green-sweat-bees.html, for photos of sweat bees.
[vi] There are some great photos of wasps at http://nativeplantwildlifegarden.com/wonderful-wasps-in-the-wildlife-garden/.