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December 2000
This season of cold and dark starts me wondering about the life hidden by the appearance of death that we name winter. Longing for colorful fragrant flowers and seeing instead seed heads and fruits, I feel especially curious about the winter fate of solitary bees, also called native or pollen bees. They are the giants of pollination, which results in seed set and fruit formation.
Of all bee species, more than 90% are solitary bees. In North America alone, there are 3500 species of solitary bees. The length of a bee's tongue and the size and structure of a flower determine, in part, which flowers each species is able to use.
With the great population decline in honeybees because of Varroa mites, attention is turning to solitary bees and appreciation for their importance is increasing. Because solitary bees don't have a large nest and many offspring to defend, they tend to be less defensive than the social honeybees. Only the female bees can sting, but do so only if they are trapped or threatened in some way.
Most of our fruits and ornamental flowers, many of our vegetables such as beans, peas, tomatoes, and squash, as well as field crops such as clover and buckwheat all depend on insects for pollination. Butterflies, moths, flies, beetles, honeybees and ruby-throated hummingbirds pollinate flowers, but solitary bees are the most prolific pollinators. Many forest trees, wild plants and forage crops are totally dependent on native wild bees.
Experts suggest that it is time to protect native beneficial bees through habitat conservation by preserving wild lands, and through the practice of sustainable agriculture. The use of pesticides in our yards, woodlots and farmlands has caused the loss of bees and other pollinators. Natural herbicides and botanical pesticides can also harm bees.
We can help their survival, and ours, by enhancing our backyards to provide for the habitat needs of solitary bees. They need nest sites and forage plants, including wild ones, which bloom all season to provide nectar and pollen.
Most bees love sun and select dry places to nest. Some species of solitary bees are ground nesters, and each female constructs a nesting tunnel underground in a sunny undisturbed location. In some species a common tunnel is used, but each female has her own chamber off the tunnel where she lays her eggs. The rest of the solitary bee species are wood- and stem-nesting bees. Of these, some excavate nests in wood and the others excavate the pith in the stems of plants such as sumac and goldenrod, making their nests in the hollowed stems.
Bumblebees are the only native bees that are highly social, like honeybees. Bumblebees, though, have smaller nests or hives, usually underground, in undisturbed meadows, woodlands or even old barns. The colonies are annual, so every individual in the colony dies each year except the mated queens, who hibernate through the winter. Each queen starts a new colony in the spring. Red clover is wonderful forage, but other nectar plants also need to be blooming before and after the clover. Bumblebees pollinate many plants including tomatoes, eggplants, peppers, melons, raspberries, blackberries, strawberries, and blueberries. For us in Maine, we should know that in the whole wide world, bumblebees are the only pollinators of potato plants!
For some species of solitary bees, the larvae overwinter in the nest, eating the stores of nectar, a source of carbohydrate, and pollen, a source of protein. The young bees emerge in the spring. In other species of solitary bees, only mated queens overwinter in the nests or hibernation burrows, and all others die in the fall. Many solitary bees hibernate most of the year, as long as eleven months, emerging briefly to work their magic.
It is the fragility of the life of bees, upon which so much depends, that affects me. One miracle of nature is that the smallest forms of life are no less important than the largest forms. This seems to me a lesson to remember.
By Nancy Coverstone (ncstone@umext.maine.edu), University of Maine Extension Educator in Androscoggin and Sagadahoc Counties
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