Throughout our Pollinator Week blog series, we’ve covered what pollinators are, why they pollinate, and how both plants and pollinators work the system. Now, let’s highlight some of the major pollinators in our area – what makes them unique, and what can we do conserve them?
Honey bees (Apis mellifera)
Honey bees have been the poster child of a major public pollinator conservation push since 2006, when a bout of Colony Collapse Disorder killed several hives and brought both our dependence on pollinators and their vulnerability to light. Honey bees, or more specifically western honey bees, are native to Europe, far western Asia, and parts of Africa, and were brought to North America by early European settlers. Honey bees in general are the most social of the bees, living in colonies that typically contain tens of thousands of individuals. Their famous honey hoarding behavior attracted human attention from ancient times, and enables them to survive long periods of famine, such as winter. However, their large perennial colonies, willingness to nest in easily constructed and managed wooden boxes, and general pollination habits have made them a staple in industrial agricultural pollination. Large numbers of honey bees are trucked onto a farm during the crop’s blooming period, then moved on to the next crop when the first crop’s flowering period is done. Honey bees in the US still face struggles, primarily from parasitic mites and the diseases they vector, but also from harsh winters, food shortages or lack of dietary variety, pesticides (many of which are used to combat the parasitic mites), and their stressful nomadic lifestyle, and hive mortality rates are higher now than they once were. However, increasing public interest in beekeeping plus the beekeeping industry’s growing ability to replace lost hives by splitting survivors has resulted in a slight increase in the number of honey bee colonies in the US over the past decade. This is a mixed blessing; honey bees are very important for our current agricultural system and can fill pollination voids where they occur, but some evidence suggests that honey bees threaten native bees through competition and sharing diseases.
Bumble bees (Bombus spp.)
Bumble bees are typically large, very fuzzy bees. They are social, with colonies typically consisting of dozens to hundreds of individuals. Each colony only lasts for one year. The smaller colonies and annual life cycle make them harder to industrialize for pollination, yet bumble bees have a work ethic that puts honey bees to shame. With their bulky bodies and thick fuzzy coats, bumble bees can maintain a higher body temperature than many other bees, allowing them to continue working at lower temperatures than most other bees. They are also buzz pollinators; unlike honey bees that stop working their flight muscles when they land, a bumblebee working a flower will basically put its wings out of gear and keep its flight muscles running (think like putting a car in park but leaving it on vs. completely turning it off). Their buzzing, vibrating flight muscles jostle pollen loose from the flower, and many flowers (e.g. tomato, blueberry, etc.) are much more efficiently pollinated by buzz pollination than typical pollination. Efforts to commercialize bumble bees for pollination have resulted in introducing and spreading new diseases to the bees; this threat, plus land use change and climate change, are putting some species of bumble bees at risk. The rusty-patched bumble bee Bombus affinis (pictured at right) has recently been added to the Endangered Species list because it has become very rare or undetectable over most of its historical range.
Solitary bees (several families and species)
Most bees are solitary, with each female producing a nest with a few brood cells and gathering just enough pollen and nectar to feed the larvae she produces. What solitary bees lack in sociality they make up with individual industriousness; many solitary bees work longer hours, in rougher weather, and/or transfer more pollen per flower visit than honey bees. The nest sites can vary, and may include hollow reeds or stems, burrows into mud, sand, or even soft stone, or tunnels bored into wood. Solitary bees rarely or never defend their nests, and “bee houses” can be set up similarly to bird houses, though they consist of bundles of straws or hollow stems and wood blocks with holes of various diameters drilled into them. Some solitary bees, such as alfalfa leafcutter bee (Megachile rotundata) and blue orchard bee (Osmia lignaria) are being developed as commercial pollinators. Some small species are attracted to sweat, and while they are not aggressive, they may deliver a mild sting if crushed against the skin. As shown in the cover photo here, solitary bees can be quite beautiful. While there has been a major surge of study on the status of native bees, their diversity of species means that the population status of many species and long-term trends are unknown. However, there is evidence that many solitary bees need major conservation action, which can be provided by providing habitat (both nesting sites and planting a variety of native flowers), using pesticides responsibly and only as needed, and economically supporting small, less monocultural farms.
Moths and Butterflies (order Lepidoptera)
Unlike bees, which rely on pollen as a protein source, moths and butterflies start life as caterpillars and, for the most part, gorge themselves on foliage. The adult life stage that pollinates flowers is basically a nectar-fueled egg- or sperm-missile, and most adults live only long enough to mate and deposit eggs. One famous exception is the monarch butterfly, which is known for its autumn migrations from Canada to Mexico. The monarch has exhibited long-term population declines in its wintering ground in Mexico; while the exact cause of this decline is not entirely clear, climate change causing adverse weather conditions during migration and while overwintering is likely to be a major contributor. Some plants are specifically adapted to be pollinated by moths or butterflies (see the title photos of moths and moth-pollinated flowers here and here), and some caterpillars offer beneficial control of noxious weeds. Many other species are relatively innocuous, functioning as a part of a large and diverse assemblage of nonspecific pollinators and feeding on wild plants. Still others are major pests, especially in agriculture.
Flies (order Diptera)
While less famous for pollinating than bees or butterflies, flies are among the most common visitors to flowers. Many plants produce flowers with bitter, rancid, or putrid-smelling flowers expressly to attract flies, though more “all purpose” flowers with sweet smells will also attract them. Some of the flies that pollinate are duped by the plant; a smell of rotting flesh can easily draw dozens of blow flies to a flower, even without a nectar reward. Conversely, flies like hover flies subsist heavily on nectar. Hover flies (Episyrphus balteatus depicted in title picture, photo credit Alvesgaspar via Wikipedia) bear special mention for a number of other reasons as well; most are mimics of bees or wasps, and the larvae are beneficial as well. Some hover fly larvae are predators, crawling over plants and voraciously devouring aphids and other soft-bodied pest insects. Others have a long breathing siphon at the tip of the abdomen that allows them to feed on watery detritus that would smother most other scavengers, making them a part of nature’s clean up system.
Beetles (order Coleoptera)
Many species of beetle are notable for their love of pollen. Most of these are innocuous, but even pest beetles such as carpet beetles feed on pollen as adults and may function as low-key pollinators. Most pollen-feeding beetles use pollen and/or nectar as a supplement to their diet, and many perform other important roles, such as preying on other insects, when they are not eating pollen.