Wild Side: It’s just a little crush

The goldenrod cellophane bee is scarce, and captivating.

Goldenrod cellophane bee, Colletes solidaginis. —Matt Pelikan

Most of the time, I’m an equal-opportunity naturalist: Everything I see holds the same interest for me, and everything seems uniquely beautiful. But every so often, this egalitarian outlook breaks down, and some particular species emerges as an object of fascination. If it’s a familiar one, watching it is all I want to do; if it’s a new one, all I want to do is track one down.

The latest in my long list of insect crushes is the tiny, fuzzy goldenrod cellophane bee, Colletes solidaginis. A big female might approach a centimeter in overall length; males are a bit smaller. The thorax of both sexes is covered with dense, yellowish hair, almost the color of the goldenrod flowers that are this bee’s favorite, indeed one might say only, food source. And the segments of the abdomen sport thick bands of fuzz, so extensive that they almost cover the entire abdomen. To my eye, it’s a beautiful insect, and that aesthetic judgment is surely part of the reason this species captivates me.

I should explain its names, both common and scientific. The species name, “solidaginis,” is easy: It refers to Solidago, the goldenrod genus that this bee depends on and helps pollinate. Literally, this is “the bee of goldenrod,” as the common name proclaims.

The rest of the common name, though, is a bit tricker. “Cellophane” refers to a peculiarity of the underground nests of all the 700 or so species in the complicated genus Colletes. Females line the brood cells of their nests with a nearly magical substance that resembles the artificial wrapping. Produced by a gland in the abdomen, this nearly impermeable lining keeps the brood cell dry enough to prevent most fungal and bacterial growth. The effect is enhanced by substances produced by other glands, which have an antimicrobial effect. This cunning chemical warfare, aimed at protecting the eggs and larvae from infection, is another factor in my fascination with Colletes.

The final cue for my obsessions with C. solidaginis is the elusiveness of this bee. It has a vast geographical range, encompassing most of the Eastern U.S., and its host plant is wildly abundant across most of that range. But rather than being an abundant bee, C. solidaginis is actually a rather scarce one, infrequently reported. There is, though, a cluster of records from southeastern New England, which appears to be the core range of this species. That made me wonder whether the paucity of Martha’s Vineyard records (prior to this year, there were just a scant handful) reflected rarity or a shortage of observer effort.

“Observer effort” is my middle name, however, and learning what I could about the goldenrod cellophane bee was one of my goals this year. When I finally found this species, I badly misidentified it, placing it in a different family altogether! But that got straightened out. At this point, I’ve seen about 25 of them at four different locations, and added 10 observations to the iNaturalist online database.

I’m by no means tiring of this bee; its behavior is fascinating. Males rarely land (when they do, it’s invariably to take a sip of nectar from a goldenrod flower); instead, they patrol rapidly over goldenrod patches, seeking amorous females. The females, meanwhile, exhibit a curious foraging pattern. They’ll methodically work a cluster of blossoms for a minute or two, but then, with no warning, abandon ship. They’ll often dart away from the area entirely, but at the least, they move to a flower a few yards away, rather than stopping at the nearest available flower head. Their flight is always rapid and erratic; visually tracking the dashing flight of such a small bee is virtually impossible.

I don’t know what they’re thinking, but my guess is that this is a predator avoidance strategy. Goldenrod, a favorite of many pollinators other than this bee, also attracts a wealth of predators. Crab spiders and ambush bugs, blending in with the yellow blossoms, wait for the unwary. Robber flies perch discreetly on leaves, waiting to bushwhack passing prey. Dragonflies skim low over goldenrod patches, ready to grab and consume any pollinator flying straight and level for too long. Feeding on goldenrod is glorious but dangerous, and C. solidaginis seems to have evolved a behavior pattern that makes it tough to catch.

While 25 individuals observed may seem like a lot, it’s actually a low count considering the amount of goldenrod I’ve surveyed. This bee, I’ve concluded, truly is scarce, occupying a small fraction of what looks to me like perfectly good habitat. That’s actually the case with all nine of the Island’s Colletes species.
Why? I haven’t a clue; perhaps these bees have highly specific requirements for the sand they nest in. In any case, having made the acquaintance of C. solidaginis, I now face the even more fascinating task of figuring out what makes it tick.