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May, 2013


by Valerie

Now that spring is well on its way to summer, bees are, well, busy. We've had enough rain to coax plenty of plants into flowering, and cool weather has given way to warmer temperatures, so conditions are perfect for this particular group of insects.

A second male trying to dislodge a mating male
(megachilidae: Anthidiellum notatum)
While many people know that there are honey bees and bumble bees, it might come as a surprise that there are also many other kinds. Honey bees certainly are the most common species seen around flowers in our area, but they are far from the only ones. We also have at least 200 species of native bees, and they range in size from huge carpenter bees topping 2 cm in length to tiny sweat bees less than 2 mm long. Some are very rare, and there are others that look so similar that it is hard to tell them apart. In fact, identifying bees is often a nightmare, partly because they are usually so active that it is hard to get a good look at them.

Even in a spot where one can watch insects closely, such as a particularly attractive flower patch, it might be hard

A mated pair (andrenidae: Protandrena sp.)
to recognize which insects are actually bees. Many flies mimic bees and some feed in much the same way. There are wasps that are similar to bees in appearance, and there are also bees that are not very hairy and might be mistaken for wasps. All these insects will come to flowers to partake of nectar, but only bees have hairs on their bodies used specifically for collecting pollen. Any insect that lands on a daisy or sunflower and quickly does a circular motion to brush against the currently blooming disk blossoms (gathering pollen) is almost certainly a bee. Large clumps of orange or yellow pollen on the legs or, in the case of leaf-cutter bees, on their bellies, are also good clues. Keep in mind, though, that male bees don't bother to collect pollen since they do not play a role in provisioning nests.

Beyond the bee basics, this is a fascinating group of insects to observe. Bees evolved from one family of wasps and, just as butterflies are mostly easy to tell from moths, so it is not too hard to figure out bees from their relatives.

Male digger bees sleeping (apidae: Melissodes sp.)
Although the social communications of honey bees are well documented, the average gardener or casual naturalist will not be able to watch these famous "dances," as they take place inside the privacy of the hive. It is easy to see, though, how honey bees arrive at certain flowers on cue, usually when the nectar and pollen are most abundant and, because they are informed back at the hive about the state of the local plants, they are frequently the first bees to take advantage of whichever flower species is currently the most productive. Many bees use whatever blossoms happen to be open at a particular time, but there are some bees that are more specialized, using only one type of flower, such as composites, mallows, or members of the squash family. Besides feeding themselves, female bees collect pollen and nectar to provision their nests, whether it is a communal hive or a solitary cell that they construct for their young (grubs). While wasp babies eat other insects and spiders, bee babies are vegetarian.

Several methods of pollen collection are used by different kinds of bees and with various types of blooms. Most flowers have pollen exposed on stamens, and the bees need only rub their hairs against the grains to get them to stick. Other blossoms have pollen in tubes, and it must be shaken out through a process called buzz-pollinating, or sonication. The sound of the bee's buzz changes quite obviously when it is performing this action. Some bees, such as honey bees, push the pollen into sacs on their legs, while others have thick hairs that collect the pollen in a looser form. The pollen hairs on leaf-cutter bees, as I mentioned earlier,

Eastern carpenter bee nectar stealing (apidae: Xylocopa virginica)
are not on their legs but on the ventral surface of their abdomen. A leaf-cutter bee with a full load of pollen looks like a sway-backed pot-bellied pig, but the underside is a bright yellow or orange color. Yellow-faced bees in the genus Hylaeus have no pollen hairs at all. The females swallow the pollen and then regurgitate it back at the nest. Almost 25% of our native bee species do not collect any pollen. These are the cuckoo, or parasitic, bees. Their relatively hairless bodies resemble those of wasps, and they lay their eggs in other bees' nests. A cuckoo bee will wait outside a nest hole during digging and provisioning and then quickly, while the rightful owner is away gathering more pollen, enter and lay its eggs.

The majority of bees seen around flowers are females. The workers in social colonies are all female and solitary females build and provision their own nests with no assistance from males. Males DO hang around flowers, though, mainly because that is the place to find the females. Large carpenter bee males hover threateningly (but don't worry - only female bees can sting) when anything enters their territory, and a few bees even mate right down amidst the flowers. This, however, is the exception, because mating for bees is a chaotic and competitive affair. Most bee couples fly high in the air or away from food sources so that they can copulate undisturbed by the numerous other males seeking to do the same. One kind of bee, in the family Andrenidae, remains in tandem as the female goes about foraging. This guarding behavior by the male means that the female is unlikely to mate with any subsequent suitors.

Leaf-cutter bee with leaf bit (megachilidae: Megachile sp.)
One other notable behavior associated with males is that of group roosting to sleep at night. Females also sleep, of course, but clusters of males are a real curiosity when they are encountered. The bees clamp their jaws on stems of plants and then just hang there; a weird way to sleep from the perspective of a mammal.

Bees have both sucking and chewing mouthparts. They sip nectar and usually use their jaws for nest construction. Leaf-cutter bees and carpenter bees are both well known for particularly strong jaws. Large carpenter bees dig out nest holes in wood. They pack pollen inside along with the egg that will hatch into a grub which then feeds on the stored food. Carpenter bees have rather short tongues and so have a hard time reaching nectar in flowers with deep throats. Their powerful jaws come in handy, though, for cutting through the base of the flower to get at nectar. Because the bee obtains a reward while not brushing against the stamens or pistil of the blossom, and thus without performing pollination, this method of feeding is called nectar-stealing.

Mason bee collecting sumac leaf material to plug its nest (megachilidae: Osmia ribifloris)

Leaf-cutter bees do not cut their signature circular holes in leaves for food. Instead, they use the pieces of leaves, and sometimes also flower petals, to line their nest, helping to waterproof it. It is quite difficult to see a leaf-cutter bee actually cutting a piece out of a leaf. They do it very quickly, and it looks sort of like somebody using scissors to quickly snip out a desired shape. In seconds, the leaf bit is severed, rolled up, and carried away in the bee's jaws and legs.

One curious behavior I just learned about is common among mason bees (Osmia ribifloris) in our area. These bees nibble the edges of leaves on evergreen sumac, making a paste that they use to create partitions and plugs in their nests (often renovated mud dauber nests). Some mason bees use mud but this species prefers leaf masticate.

With the current interest in native bees due to their importance for pollinating a large variety of plants, it doesn't hurt to learn more about their behaviors and habitat needs. Yes, bees can sting. But, no, I've never been stung by a bee I was watching. It's the ones that I do not notice that let me know when I've accidentally put my hand on them!

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