Each spring, as melting snow liberates the forest floor, I seek out wildflowers. I flip through Newcomb’s Wildflower Guide, counting petals and leaves to tell hepaticas apart and to sort bellworts from trout lilies.
Last spring, my eye was drawn to some curious beetles clambering on trout lilies. Scarcely as long as my pinkie fingernail and with black heads, the slender beetles had grooved, black elytra, or hind wing coverings, that characterize beetles. But the beetle’s most striking feature was its brilliant burnt orange thorax.
Bright colors in nature typically mean “stay away,” so I avoided handling my newfound friends. I subsequently learned that the beetles were red-necked false blister beetles (Ischnomera ruficollis, until recently classified as Asclera ruficollis), and as their color and name suggest, they should be handled with care.
False blister beetles (Family Oedemeridae) are easily mistaken for true blister beetles (Family Meloidae), but a close look distinguishes the two: in true blister beetles, the head is usually wider than the segment behind it (the pronotum), giving the impression of a distinctly narrow neck; the false blister beetles’ pronotum is widest at the front and partially covers the head so that they appear to lack a neck.
Both of these beetle families produce cantharidin, a noxious compound that raises painful blisters on those who can’t resist the urge to smack generally harmless beetles that happened to land on their skin. The blistering agent is released from the insect’s mouth and leg joints, but only when the beetle is threatened, poked, or squished – accidentally or otherwise.
Cantharidin is the active ingredient in “Spanish fly,” a product once sold as an aphrodisiac, despite the fact that its toxic effects rival those of strychnine. Cantharidin famously poisoned a couple of London women in the 1950s, and pediatric cases caused by ingestion of beetles are not uncommon. Poisoning of horses is more common because blister beetles are sometimes baled in hay. I’m not sure how much of the deadly chemical is in a single beetle, but it is fair to say we should treat blister beetles (true or false ones) with respect.
I wondered what these beetles were doing out and about with overnight air temperatures below freezing. “Pollination” was the short answer, but there was more to it than the exchange of nectar for pollination that we learn about in grade school.
Unlike more familiar pollinators that move pollen among flowers while foraging for nectar, false blister beetles get most of their calories by actually eating pollen. This departure from the symbiotic sugary-reward-for-services view of pollination may seem surprising, but it’s a quite common behavior. Pollen consumption occurs in bees, ants, moths, beetles, birds, and even a few spiders.
But consuming pollen is just a first step in utilizing this food source. Pollen is considerably resistant to breakdown. It is so durable that intact pollen from ancient bogs is used to infer which tree species occurred in millennia past. Very specific sugar concentrations found on target flowers’ stigma split the pollen’s “test,” or outer coating, so that pollen tubes grow and fertilize eggs to grow seeds. Digestive enzymes in the false blister beetles’ gut have a similar effect causing pollen grains to germinate, opening the protective test, and converting pollen grains from unassailable citadels to nutritious beetle fodder.
Pollen consumption might seem predatory, but messy foraging beetles transfer enough uneaten pollen to pollinate flowers. Pollen traits have evolved to encourage this behavior; many flowers produce colorful pollen enriched with nutritious liquids to attract foragers. These traits do not occur in wind-pollinated species.
Many spring flowers rely less on seed production for reproduction than do later blooming species. Instead, these species reproduce by clonal spreading. In one hepatica population, red-necked false blister beetles were just about the only pollinators, and most flowers went unvisited. A small fraction of trout lilies flower in a given year, and few produce seed. When researchers pollinated trout lilies, fewer than half produced fruit.
Seeds contain gene combinations absent in clones. This is nature rolling the dice to bet against change. In an unchanging environment, cloning would be just fine, but as circumstances change, one or more seeds may have characteristics to thrive in a new environment.
Spring flowers, in addition to being essential food sources, are important gathering points for beetles seeking mates. Many of the beetles I observed were paired: males with usually larger females. Perusing images on iNaturalist, I can see that mated beetle pairs are common on trout lilies.
With beetle reproduction accounted for, you may wonder what happens next. But science does not yet have the answers. Beetles in this family lay eggs under tree bark; some false blister beetle larvae drop to the soil and consume plant roots; others bore into rotting wood. As a scientist, I find it awe inspiring that many mysteries remain unsolved; if nothing else, I suppose it provides job security.