We haven’t seen honeybees in the garden for several years, but pollination efforts have been amply taken care of by a variety of hymenoptera from tiny sweat bees to larger bumblebees and several types of wasps as well.
The swamp milkweed is in full flower, and emits a sweet fragrance that pulls in quite a few different pollinators, as well as a specialized group of munching herbivores that are
well adapted to handle the toxic cardiac poisons (glycosides) it sequesters in its leaves and stems (but perhaps not its flower nectar). Yesterday, the plants were full of
bald-faced hornets, a long legged black and white wasp (not a hornet taxonomically speaking), known for its painful, repetitive stinging ability. They are social and nest in a large papery hive constructed by all the workers, but they seemed to aggressively exclude each other from the particular flowers on which one is foraging.
My camera equipment is inadequate to get good closeups of this less than 1-inch long insect, but this photo shows the striking black and white coloration well); from (http://bugguide.net/node/view/279221/bgimage). For more information and some really great close-up photos, go here: http://www.cirrusimage.com/Bald-faced_hornet.htm .
The hornets moved pretty quickly around each flower cluster, thrusting their heads deep into each flower as they moved along. It was somewhat comical to watch them try to leave that flower cluster, because the milkweed flower has a unique pollination mechanism that traps the insect’s leg in a tiny cleft where they get stuck until they are able to remove the saddlebag of pollen in that cleft. The hornets pulled, twisted, buzzed, and hung from the flower until they could manipulate it just right to escape. Most of the hornets had multiple bags of pollen attached to the spines on their lower legs (which you can faintly see as light yellow oblong structures attached to the end of their leg).
The milkweed’s strategy is to reward the insect with just a drop of nectar so that
it moves to other flowers, gets its leg stuck once again and deposits the saddlebag of pollen in another, different flower and… voila, pollination.
Bumblebees avoided the milkweed preferring the bee balm and the coneflowers instead. These flowers don’t seem to offer much of a nectar reward because the actual flowers in the composite head are tiny and narrow. However, it turns out that bumblebees have really long tongues, complete with little brushes on the end of them, that enable the bees to reach into a narrow slot and slurp up even the tiniest drop (http://www.bumblebee.org/bodyTongue.htm). They are pretty hard to photograph close up, because they are continually on the move, testing each flower in the head for
nectar and stopping only infrequently in any one flower for just a few seconds.
Below - bumble bee on purple coneflower:
Above: bumblebee on Bee Balm (Monarda)
It is due primarily to the services of our local bumblebees that we had such a fine raspberry crop this summer. In June, the raspberry plants were thick with several species of bees, but the bumblebee, in particular, is an incredibly efficient pollinator. Apparently they develop electrostatic charge as they fly, so that when they land on a flower, the pollen attaches itself to their fuzzy thorax and leg spines. When they move on to another flower, the receptive stigma of that flower attracts the electrically charged pollen away from the bumblebee, and again, voila…pollination. Another amazing feat bumblebees perform to collect pollen (which they feed to their larvae) is to “buzz” the flower at a frequency that causes the pollen sacs on the flower’s anthers to open and dust the bee. The bees groom themselves when they get back to the nest, depositing their pollen for workers to feed the larvae. However, while out foraging, there is an abundance of pollen on them that finds its way onto theappropriate flower receptacle. Some people claim that these characteristics make bumblebees far better pollinators than honeybees.
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