ean honey bee (Apis mellifera) is the most important crop pollinator in the United States. However, because of disease and other factors the number of managed honey bee hives in the United States has declined by 50 percent since. During this same period, the amount of crop acreage requiring bee pollination has continued to grow. This makes native pollinators even more important to the future of agriculture.
Native bees provide free pollination services (as opposed to honey bee which are typically rented) and are often specialized for foraging on particular flowers, such as squash, berries or orchard crops. This specialization results in more efficient pollination and the production of larger and more abundant fruit from certain crops. The pollination done by native bees contributes an estimated $3 billion worth of crop production annually to the U.S. economy.
Native bees come in a wide range of colors and sizes, from tiny sweat bees less than a quarter of an inch long to bumble bees over an inch in length. Most are solitary, with each female creating and provisioning her nest without the support of a caste system of workers.
About 70 percent of native bees excavate underground nests while 30 percent of bees nest in wood tunnels, usually pre-existing holes such as those made by wood-boring beetles, but some will chew out the center of pithy twigs. In the case of both ground-nesting and wood-nesting bees, once the nest is complete, the mother bee generally dies. Her offspring will remain in the nest, passing through the egg, larva and pupa stages before emerging as an adult to renew the cycle. For some species this life cycle may progress over a matter of weeks, resulting in a second generation of bees in a single season. A few species may remain dormant for over a year. Most solitary bees however complete this life cycle over the course of a full year.
Native bees often only live for a few weeks as actively flying adults. They mate immediately upon emergence and the females begin nesting. They lay relatively few eggs compared to other insects, with a single female often laying less than 50 eggs before she dies. Male bees do not live long beyond mating, they do not collect pollen and have little value as pollinators.
While most of these wood-nesting and ground-nesting bees are solitary, some are gregarious, preferring to nest near others, a behavior that allows large aggregations to develop in favorable locations. Only a few tunnel and ground-nesting bee species ever develop truly social colonies, and often such behavior is environmentally dependent with some bees being social in one situation and being solitary in another. The one group of strictly social bees native to the United States is the group of approximately 45 bumble bee species.
The two habitat components need to be close enough together so that the bees can fly between them. The flight distance of a bee varies with the size of the bee. Small sweat bees and mining bees may not fly more than 200 or 300 yards from nest to forage area. Large bees (bumble bees, for example) can cross a mile or more of inhospitable, flower-less landscape to forage. But however large the bee, if it has to fly too far the effort begins to outweigh the benefits and the bee may either find somewhere else to nest or not survive in the landscape.
A third factor that influences habitat is insecticide exposure. To thrive, bees need minimal exposure to pesticides.
The Apidae are a large family of bees, comprising the common honey bees, stingless bees (which are also cultured for honey), carpenter bees, orchid bees, cuckoo bees, bumblebees, and various other less well-known groups. The family Apidae presently includes all the genera that were previously classified in the families Anthophoridae and Ctenoplectridae, and most of these are solitary species, though a few are also cleptoparasites. The four groups that were subfamilies in the old family Apidae are presently ranked as tribes within the subfamily Apinae. This trend has been taken to its extreme in a few recent classifications that pla