late summer or fall, the resident queen wears out and dies, and the nest ceases to function as a colony. The workers and males die when the weather turns cold.
Sweat bees (Halictinae) are Missouri's other group of social bees. There are at least 70 species of sweat bees in Missouri. Most are small and inconspicuous and have not been studied. Some are solitary, but a number are known to be social. Like the bumblebees, they live throughout the state in all habitats. True to their name, they have the habit of landing on human skin to lick perspiration.
Bees are among the few insect groups that build nests, and the females do all the work. Nests contain one to many cells. A cell is where a single bee usually develops to adulthood. The architecture of these nests varies tremendously, depending on the kind of bee. Many ground-nesting bees build simple, shallow holes in the ground, sometimes with side branches, while some social sweat bees create elaborate underground labyrinths with many branches. Certain leafcutter bees string together a linear series of leafy cells inside a hollow twig. Other species related to the leafcutters attach fragile, resinous globes to twigs or under rocks.
Some bumblebees may convert a mouse or bird's nests into a wax-based dwelling. Nests are valuable in the bee world and are sometimes aggressively stolen by other bees.
Certain bees take this behavior a step further. While most bees make their own nests, there are some kinds of bees that mimic the habits of the cowbird. Referred to as cleptoparasites (or parasitic bees), these bees do not collect pollen or make nests, but use the nests of non-parasitic species as their own. The "host" bee usually doesn't even realize it.
Unlike the cowbird, which parasitizes the nests of many different kinds of birds, parasitic bees are usually much more particular about their hosts. Bees that attack leafcutter bee nests don't attack sweat bee nests, and vice versa. Because of the absence of pollen-collecting hairs on their bodies and their often slender physiques, parasitic bees often look more like wasps than bees. Nearly 100 species of bees in Missouri are parasitic.
Bees are important pollinators of plants in Missouri, and nearly everywhere else. Without pollination, plants could not reproduce sexually, and there would be far fewer seeds or fruits. To produce their full complement of seeds, most flowers require multiple visits by pollinators, not just one. Bees are superior pollinators because of their reproductive requirements for pollen and nectar, their adaptations for collecting pollen and their habit of visiting flower after flower. They transfer many pollen grains to plant stigmas (female reproductive organs in plants) and effect cross-pollination more dependably than any other insects.
In addition, bees display flower constancy, which is the habit of visiting flowers of the same species consecutively during a foraging trip. In this way, plants are cross-pollinated with "the right kind" of pollen.
Over time, many plants have developed pollination systems that depend on bees. Missouri examples include most of the flowers in the bean family (Fabaceae), the daisy family (Asteraceae), the rose family (Rosaceae), gentians and many others. Many native fruits eaten by birds and other wildlife develop from flowers that are bee-pollinated, such as blueberries, plums, serviceberries, buckthorns and ground cherries.
Some flowers require certain kinds or sizes of bees for pollination. Wild indigos, which are common on prairies and glades, have large flowers that can be pollinated only by large, strong bees, primarily queen bumblebees.
Far from being threatening, our native bees are the core component of a pollinator force that powers much of natural Missouri. They carry it-and us-across the void of winter into the growing seasons, from one year to the next, from generation to generation.