Much has been made recently, in both the popular and the scientific press, of a “pollinator crisis” — sharp declines in the populations of the insects that transfer genetic material in the form of pollen from one flowering plant to another. The mingling of genes that results is essential to the well-being of many species of plants, and many insect studies and surveys suggest the crisis is a real one.
Poster child for the worrisome situation is the honeybee, a semi-domesticated species native to Eurasia that is now a worldwide workhorse for agricultural pollination. A mysterious syndrome, apparently the result of converging stresses including pesticides, parasites, and climate change, has been decimating honeybee hives, reducing the productivity of many food plants for want of adequate pollination.
Receiving much less attention, among the general public if not among biologists, is a similar decline in the numbers of many pollinators that are native to our continent, including hundreds of species of native bees. Again, the reasons behind the trend are not entirely clear, but habitat loss and toxins in the environment are surely factors. Partly because of the concerning state of our bees, and partly because bees turn out to be fascinating little animals, a lot of my time in the field so far this year has focused on bees.
And it is getting to be prime time for observing these diverse insects, many of which play fascinating ecological roles and/or display surprising beauty. My sense is that despite any downward trend in numbers, many of our native bees are especially abundant this season. Perhaps the deep snow cover during much of winter represented an insulating layer that enhanced survival.
Nearly any kind of flower will attract bees, though some flowers work better than others and some bee species show a strong preference for particular plants. Among the wild plants currently in bloom, American holly seems to be a particular favorite of bees; a holly bush with even just a few flowers in bloom will often prove to have a half-dozen types of bees working on it.
In contrast to the honeybee, famous for forming huge colonies presided over by a single queen, the vast majority of our native bees are so-called solitary species: They may nest in loose aggregations, but each nest is built, maintained, and provisioned by only a single bee. In most cases, the nests are tunnels dug into the ground by a female bee, which lays eggs in the bottom of the tunnel and stocks the nest with pollen for the young bees to eat when they hatch.
Other types of bees nest in wood, either hollowing out the pith of a dead stem or chewing a hole into a dead branch (or, inconveniently, untreated wood on someone’s house). Wood-nesting bees do not appear to be especially well represented on the Vineyard, but that doesn’t mean they’re not important: Some of these bees are important pollinators for particular flowering plants.
A multiyear study led by entomologist Paul Goldstein, with assistance in the field from dozens of Vineyard “citizen scientists,” produced a valuable general picture of our bees. The study collected thousands of bees, and documented more than 160 species on Martha’s Vineyard — about half the bee species known to occur in Massachusetts. This study, with fieldwork completed in 2011, provides a precious baseline of data on the Island’s bees.
Still more information is available online or in scientific publications. Since bees play such important ecological roles, they are rather well studied by insect standards, and with a little digging, it’s often possible to identify a bee you photograph well, or to learn about its life history. But many questions remain unanswered, and because of the sheer diversity of bees (which translates to many closely related species), identifying them is often difficult.
For example, I recently photographed an elegant, half-inch-long bee visiting holly blossoms outside my office. Endowed with a bright red abdomen, this insect was easy to pin down as a “sweat bee” in the genus Sphecodes. But on referring to Dr. Goldstein’s study, I found that a full dozen Sphecodes species have been documented here, all virtually identical in their external appearance! The odds of determining the actual species my bee belongs to are slim indeed.
Other groups are easier. We have, for instance, only one large carpenter bee (and it’s one of the few native bees that might be considered harmful to humans, since it chews deep tunnels in shingles and trim on houses). And the Island has only three other carpenter bees, smaller insects in the genus Ceratina (and all much more benign, since they generally tunnel into dead branches).
Our native bees are ecologically helpful animals, and they’re gentle ones, too, disinclined to sting unless seriously molested. Help them out by minimizing your use of toxic chemicals, and by tolerating some untidiness in your yard and garden: Standing dead vegetation, downed tree limbs, and exposed mineral soil — all anathema to most gardeners — are resources that bees depend on for survival.