Marin IJ Articles
July 23, 2011
THERE'S A WHOLE LOT of buzzing going on — bees are busy doing their thing, zipping from flower to flower, moving pollen from one to the other, bringing the promise of plump peaches, tasty tomatoes and humdinger zucchini. There are also ones that might be drilling little holes in the eaves of your roof or fabricating what looks like upside-down mud pies, others stealthily cutting perfect circles in your rose leaves, and those laggards hitching a ride on your arm while you have a sweaty jog with your dog.
Are these all bees? Not exactly.
Bees, ants and a large number of other insects collectively called wasps are members of the order Hymenoptera, or membrane-winged insects. Many are social insects, like true ants, but the majority are solitary. Honeybees, likely the most well-known member of the family, do their good deeds of pollinating plants and making honey, while their more nefarious relatives, the yellowjackets and hornets, are the dreaded, uninvited guests at summer picnics. Then there are mud daubers, carpenter, mining and leafcutter bees, paper wasps and cicada killers.
What's the difference among these critters, and should you be concerned about them?
A few general features help distinguish bees and wasps — bees usually have hairy bodies for pollen collecting, wasps tend to have few hairs to none at all. Wasps have more elongated bodies, longer legs and often a pinched-looking waist, whereas bees appear more compact.
Most bees purposefully collect pollen; wasps are predominantly carnivores and may be incidental pollinators as they seek their prey. Social bees make nests of wax; most social wasps make nests of paper. Only the honeybee, Apis mellifera, produces a perennial hive. Other bees and wasps may be social (yellowjackets) or solitary (mining bees), but their hives die out at the end of the season, and only the queen survives, seeking a place to produce a new hive in the coming season.
Bumble bees (Bombus spp.), those roly-poly, furry looking, orange or yellow and black striped bees that seem to lumber between flowers, are social bees that build nests in existing cavities, usually on or in the ground — abandoned mouse or bird nests, dry leaves, outdoor furniture cushions or other loose "fluffy" material. Not generally aggressive, they don't hesitate to sting if their nest is threatened.
The majority of bee species don't produce a colony. Solitary bees, a large group of plant pollinating small-bodied bees, are not aggressive and stings are quite mild. The inch-long industrious carpenter bee (Anthophoridae family) drills perfectly round holes in the wooden eaves of buildings, creating tunnels in which to lay eggs. Although they are considered wood-destroying insects, the damage they do is typically limited to surface wood, not structural or weight bearing wood. Though solitary, these bees often build nests close to others, and their numbers can grow.
Ever notice a bee hovering around the ground? Mining or digger bees (Andrenidae and Anthophoridae families) are about the size of honeybees or smaller; some are brightly striped, others are a shiny metallic green. They nest in the ground and large numbers of these bees may nest near one another if soil conditions are right. Though they may be considered a nuisance, mining bees are not aggressive and seldom, if ever, sting.
Leafcutter bees (Megachilidae family) are stout-bodied, black bees about the size of a honey bee, and are important pollinators of wildflowers, fruits, vegetables and other crops. They cut the leaves of almost any broadleaf deciduous plant to construct nests in soil cavities or holes (usually made by other insects), in wood and in plant stems.
Sweat bees (Halictidae family) rarely sting except when pinned against the skin. These plant pollinators get their name for their habit of landing on people and licking the perspiration from the skin for the salt. Most are generally are black or brown, though some species are bright metallic green or brassy yellow.
Social wasps are notorious for creating unsightly nests around the house and garden, and spoiling summer barbecues with their scavenging habits. Most rear their young on a diet of live insects, except for the western yellowjacket (Vespula pensylvanica) that scavenges dead insects, earthworms and garbage. Social wasps construct nests of paper, produced by chewing on wood, scraps of paper and cardboard, and sting for defensive purposes only. If they feel threatened, they are capable of repeatedly stinging without dying. About 90 percent of all stings are likely caused by yellowjackets.
Hornets and paper wasps are common social wasps. The baldfaced hornet (Dolichovespula maculate), an atypically large, black and white yellowjacket, builds distinctive pear-shaped, basketball-sized nests covered with grayish paperlike material in trees, shrubs or under building eaves. They rarely sting unless the colony is seriously disturbed. The western paper wasp, Mischocyttarus flavitarsus, makes open-cell paper nests under building overhangs. More slender-bodied than other social wasps, they are predators of caterpillars and other insects.
The solitary mud dauber (Sphecidae family) constructs nests of mud on porches, decks and under roof overhangs around homes; they are potentially a nuisance but generally are not aggressive and don't defend their nests. Ranging in size from extremely small forms to the large, fearsome looking cicada killers, a number of solitary wasps nest in the ground with life cycles similar to mining bees. The cicada killer (Sphecius speciosus) resembles a jumbo yellowjacket that captures and paralyzes cicadas. Despite their intimidating appearance, these insects are inoffensive and usually will not bother people even when provoked.
There are a number of bees and wasp imposters — insects that look like honeybees but aren't. The clear-winged moth, Sesia apiformis, is as large as a hornet but has more yellow and lacks the tiny waist. Both syrphid flies (Syrphidae family) and robber flies (Asilidae family) also look like bees, but have only one pair of wings.
Knowing what's buzzing around your garden can help you make choices about what, if any, control measures you want to take. Keep in mind that, in spite of their nasty reputations, hornets and yellowjackets can be beneficial, preying on many insects we consider pests. Also, as their colonies are not perennial, you may choose to simply wait until the colony dies out in late fall or early winter. The nest will slowly deteriorate from weather or from attack by hungry birds.
The University of California Marin Master Gardeners are sponsored by UC Cooperative Extension. For questions about gardening, plant pests or diseases, call 499-4204 from 9 a.m. to noon, and 1 to 4 p.m. weekdays, or bring in samples or pictures to 1682 Novato Blvd., Suite 150B, Novato.
• UC IPM website, www.ipm.ucdavis.edu/PMG/menu.homegarden.htm• Colorado State University Extension website, "Nuisance Wasps and Bees," by W.S. Cranshaw, www.ext.colostate.edu/pubs/insect/05525.html