Sept/Oct 2018For Wildlife Watchers: Hummingbird MothBy Rob Simbeck, Photo by Tes Jolly
Hummingbird moths, or clearwing moths, seem to mimic the hummingbird’s signature feature, albeit with four wings rather than two.
Adaptation doesn't have to be dramatic. It is, after all, simply the process of gaining advantage in a given environment. It can seem quite pedestrian when it involves a longer beak, thicker fur or better camouflage.
But then there are the adaptations that can only be described as magical. The development of the eye, which happened several times independently, speaks to a wondrous use of the cells at hand. Viewed through the right lens, the resulting ability to apprehend and analyze the world from a few inches or a few miles away is nothing less than a superpower.
As is flight. The ability to lift off at will from the planet has captivated humans for eons, leading us to posit everything from angels to Superman.
Flight has evolved on three separate occasions - in insects, birds and bats. Each has mastered the physics of lift, drag and stability. And then, on a few occasions, evolution has taken it a step further with that wondrous, Tinkerbell-tinged subset of flight known as hovering. Hummingbirds offer the best-known example, but there are nectar-sipping bats that have mastered the art as well, along with a few insects.
One of the most impressive for wildlife watchers is the group of moths known as hummingbird moths, or clearwing moths, which seem to mimic the hummingbird's signature feature, albeit with four wings rather than two.
Those wings are very different in construction and operation. A hummingbird wing's light bones and flexible feathers allow for the twists and turns, arches and flexes that cause the swirls and eddies creating low pressure above and lift-creating higher pressure below, at a rate of about fifty beats per second. The hummingbird moth operates with narrow wings comprised of stiff yet flexible membranes beating even faster - eighty-five times per second - in a shallow figure-eight pattern that creates lift and a barely audible hum. Hovering bats, by comparison, make do with fewer than twenty beats per second.
The practical application of hovering is the ability to station oneself in front of a nectar-producing flower while dining. The hummingbird uses its tongue to collect that nectar; the hummingbird moth uses an inch-long proboscis, normally coiled, pollinating as it goes.
At first glance, it's not uncommon to mistake the hummingbird moth for its namesake. "Almost every year," says biologist, researcher and author Beatriz Moisset, "an excited visitor to the local nature center tells us that he or she saw a tiny hummingbird unfurling a very long tongue. We have to explain that they saw a moth, not a bird."
Hummingbird moths are members of the sphinx moth family, which has about 1,500 members worldwide, mostly in the tropics, and 125 in North America. There are three species of hovering moths in South Carolina - the hummingbird clearwing, the very similar slender clearwing (found along the coastal plain), and the snowberry clearwing. Both the hummingbird and the snowberry are widely present in the state wherever their host plants are plentiful.
(Hummingbird clearwing Hemaris thysbe, Slender clearwing Hemaris gracilis, Snowberry clearwingHemaris diffinis)
Description: One and a half to two inches in length. Thick-bodied and clear-winged.
Habitat and Range: Much of the eastern U.S. and across Canada to Alaska. Throughout South Carolina in meadows and gardens with nectar-producing plants.
Viewing Tips: Large, hovering insect often mistaken for a hummingbird. Watch food plants like honeysuckle.
Both are large, from one and a half to two inches in length, with heavy prawn-like bodies, olive-green toward the front and darker with reddish bands toward the back. The hummingbird moth has pale legs, and the snowberry clearwing has black legs. The male's flared tail can make it look somewhat like a crawfish.
The eyes of these moths are comprised of tiny facets containing a lens and photoreceptor cells, which gives them multidirectional vision. Those cells are packed more tightly in the center, which means they see best the objects directly in front of them.
The female releases a pheromone from glands at the tip of her abdomen to attract a male. She lays tiny green eggs singly on host plants such as honeysuckle, hawthorn and snowberries. The yellowish-green caterpillars, with light green lines along the back and red spots along the abdomen, are among many called hornworms, because of a hornlike protuberance on the tip of the tail. They consume the leaves of the host plant and grow for several weeks. If they live through that stage - they're a favorite food of many birds - they will crawl or drop to the ground and spin a thin, loose cocoon amid leaf litter. Eggs laid early in the summer produce pupa that re-emerge in a few weeks. Those laid in the fall will overwinter and emerge as moths in the spring. In the North, with a shorter summer, there is only one generation, with the pupae overwintering.
When the adult emerges, its wings are initially covered with deep reddish-brown to black scales, but those slough off in the first flight or two, leaving transparent wings with dark red borders.
Adults feed on the nectar of plants that include butterfly bush, bee balm, verbena, honeysuckle, phlox, hawthorn, azalea, blackberry, cherry, plum, trumpet vine and dogbane. Given that variety, they may be seen in gardens as well as in meadows and forest edges. Making it easier on wildlife watchers is the fact that they are daytime feeders, generally visible from March through September in South Carolina.
The caterpillars can be problematic for some berry crops, but not as great a problem as the tomato hornworm, the caterpillar of the five-spotted hawkmoth.
The hummingbird moth is a useful pollinator with few predators. It is susceptible to loss of habitat through development, a process that slowly robs us of the evolutionary magic that has brought them to our fields and gardens.
It's magic Rita Venable, author of Butterflies of Tennessee, knows well.
"When I am outside on a field trip or gardening and I see one of these species," she says, "it is a three-step process to identification. At first, I think, ‘Wow, that's a big bee!' Then, ‘Oh, wait, it's a hummingbird!' Then, finally, I realize that there is no buzz. ‘Oh, it's a clearwing moth!' It's a surprise party every time I see one, especially with other people around, because you just don't expect it, and they are so very quiet."
They are indeed magical, and theirs is magic worth viewing.