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Field & Street

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These are the longest days of the year, and it seems like we need every minute of them to squeeze in all the stuff that is happening. During the past two weeks I have watched a pair of blue-gray gnatcatchers building a lovely nest of lichens bound together with spider's silk. I have watched Baltimore orioles feeding their young in hanging nests and discovered fire pinks blooming by the hundreds in my favorite oak woods.

The season advances. The spring flowers have all gone to seed. The flowers of high summer--the bee balm and blazing star, the obedient plant and brown-eyed Susan--will soon burst into bloom. In my backyard I am seeing small bumblebees, the first-born workers of the year.

When our cherry trees came into flower in late April, the bumblebees that fed on--and pollinated--the blossoms were giants nearly an inch long. These were the queens produced by last year's colonies late in summer. An entire colony of honeybees can live through the winter, but only the queens of the bumblebees survive. When they emerge from their winter shelters in April and May, the burden of carrying on their line rests entirely on them.

Bumblebee queens spend the winter underground, and when they wake from their hibernation they immediately start looking for another underground refuge where they can create a nest. According to the books, they look mainly for rodent burrows. My guess is that in the city they also find holes in foundations, wide cracks in concrete, and rotting corners of garages.

Once she has found a suitable location, the queen starts building. Using wax secreted by glands in her abdomen, she builds a shallow cup on the floor of the nest cavity. She places a ball of pollen in the cup and then lays eggs on the pollen. Finally she roofs the egg cell with more wax, sealing the eggs into the spherical chamber. Meanwhile, she is also building a honey pot near the entrance to the nest where nectar gathered from flowers will be placed.

The eggs will hatch into larvae that will be fed on pollen and nectar for the week to ten days until they are ready to pupate in cocoons, from which they will emerge as adult workers. While the first brood of young workers is developing, the queen must collect enough pollen and nectar to feed them; she also builds more chambers and lays more eggs. By the end of the season colonies of some species may contain as many as 400 workers.

Bumblebees belong to the genus Bombus--this Latin word refers to a low rumbling sound, which nicely describes the noise of their vibrating wings. Nearly all of the 200 or so species of this genus live in the northern temperate zone, although there is one species in the Amazon and a few others as far south as Tierra del Fuego. Two species occur on Ellesmere Island, which is far north of the Arctic Circle.

The fact that only the queens survive the winter may be an advantage for these insects in cold northern situations. They do not need to find winter refuges for large numbers of individuals, as honeybees do.

The social organization of bumblebees is in many ways simpler than that of honeybees. The workers that hatch from the first eggs laid by the queen bumblebee are just smaller versions of her, and in some species the largest workers may be bigger than the smallest queens. In honeybees there are significant morphological differences between queens and workers.

There is some division of labor among bumblebees based on size. Very small workers are more likely to remain in the nest tending young and doing the housekeeping. The larger workers leave the nest to forage for pollen and nectar. However, the individual worker may move from one job to another during its life.

Bumblebee society can be seen as a dominance hierarchy, one that is maintained in part by brute force. Workers will sometimes try to steal and eat newly laid eggs. The queen attacks the would-be miscreants with feet and mandibles, and occasionally these attacks result in serious injury or even death. The attacked workers do not resist, but they try very hard to escape.

Egg-stealing behavior wanes quickly, and after a few hours of vigorous defense by the queen, stops altogether. The former thieves then become attentive nurses of the young. However, the queen will continue to be aggressive toward the workers, especially those whose ovarian development is nearly as great as her own. Head butting with mandibles agape is the usual tactic. Even though bumblebees have reusable stingers, they don't use them on one another.

In the highly developed society of the honeybee the queen keeps the workers in line with pheromones that she emits, which prevent any reproductive development by workers. Honeybee young are treated differently too. Each larva has its own individual cell where it is fed and tended by its nurses. Among bumblebees, small groups of larvae share an egg cell. Food is placed in the cell, but it is up to each larva to find and eat its share. If food is scarce, there can be serious competition.

Bees as a group are the evolutionary descendants of predaceous wasps, but bees (except the rare egg-stealing worker) have gone totally vegan. Their sole foods are pollen and nectar gathered from the blossoms of flowering plants. Pollen is a rich food source. Grains are as much as 10 percent fat and 30 percent protein. From the plant's point of view, the purpose of pollen is to fertilize ovules and create a new generation. But nectar serves solely as an inducement, a reward for the pollinator. Nectar is mostly water, but it contains various sugars-fructose, glucose, and sucrose-as well as some proteins, fats, and even B vitamins.

A bee swallows the nectar it collects, using some for its own energy needs but shunting much of it into a special honey stomach. The swallowed nectar is regurgitated in the nest along with enzymes that carry on the conversion from nectar to honey. That luscious stuff on your morning toast is actually bee spit.

Raising one young bee to adulthood requires the nectar and pollen gathered during 3,000 flower visits. A bumblebee colony that grew from one queen in early spring to 400 individuals by the end of summer would need 1,200,000 flower visits. Hence the term "busy bee."

Watch your neighborhood bumblebees at work. Their size and strength make them very good at pollinating flowers that hide their pollen and nectar. The bumblebee can muscle its way into a flower with a long corolla and get at the riches within. Look at a bee's hind legs. You will probably see large, pale masses clinging to the upper parts of the dark limbs. Bumblebees--and honeybees--have specialized structures called pollen baskets on their hind legs. The mass of pollen is held together with nectar. Thanks to these pollen baskets, a bumblebee can carry as many as 15,000 pollen grains. For the insect, this means longer foraging trips, with more time to collect food and less time spent commuting.

My experience has been that it is the bee you don't see that stings you. You can stand and watch a bee at work from just a few feet away without worrying too much about getting stung. If a bee takes an interest in you, perhaps checking out a shirt the same color as its favorite flower, the best strategy is to ignore it. It will go away. Still, you might want to take pains to breathe through your nose. I once accidentally inhaled a yellow jacket, with rather unpleasant results.

As the season advances and the queen adds more workers to her support staff, the colony will begin to produce young queens and males. The males of some species hang out near the entrance to the hive, waiting for an unmated queen to emerge. In other species, the males wait near flowers ready to approach anything that looks like an unmated queen.

The mated queens will start looking for underground locations to spend the winter. The males, this year's workers, and the old queen will pass with the coming of frost. When spring returns, the mated queens will rise from their burrows and start the whole process again.

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