Creature Feature: Bumblebee Moth, Hemaris diffinis

June, 2011

           With all due respect to Darwin’s finches, platypi, and any number of dinosaur species, my nod for evolutionary mascot goes to Hemaris diffinis, the Bumblebee moth.  A member of the Hawk moth family (Sphingidae), it measures 1.5 to 2 inches in length, and is also known as the Snowberry clearwing. This name refers to the wings, which unlike those of other moths, are translucent.  Bumblebee moths are widely distributed throughout North America, and can found on a variety of wildflower and garden species.  Hemaris are one of the only moths that forage actively during the day.  Like other moths, Hemaris have long, slender tongues (sometimes longer than the rest of the moth) which are rolled up when not in use, which allow them to forage deeper into flowers than other insects.  Four species of Hemaris can be found in North America, including the hummingbird clearwing, H. thysbe, which occurs locally. 

            Discovery of the bumblebee moth caused early biologists to reconsider the trusted adage: “if it walks like a duck and quacks like a duck, well...”  The bumble bee moth presents two evolutionary tricks to enhance its survival: convergent evolution and mimicry.

            Convergent Evolution, more obtusely referred to as homoplasy, occurs when species that are unrelated develop similar traits. A well-known example is the ability to fly shared by bats, birds and insects.  These did not arise from a single flying ancestor; rather, environmental conditions provided a niche for flying things, and representatives from different groups filled in.  Evolutionary changes resulting in the ability to
fly took millions of years, naturally. 

            The act of “humming”, loosely described as rapid sustained wing beats, presents an efficient feeding technique which allows Hemaris (and hummingbirds) to hover while feeding, allowing for quicker escape from predators.  Most other pollinators land on flowers they are visiting, while  Bumblebee moths move swiftly between flowers.  There are two species of Hemaris in our area,
but only H. diffinis poses as a bumblebee.

            Mimicry is when species take on the appearance of another, usually one less tasty or more heavily armed.  H. diffinis employs the latter technique, specifically called Batesian mimicry, trading on the venomous reputation of the bumblebee (Bombus).  An H. diffinis I
observed recently feeding on rosemary, was
doing a credible rendition of Bombus vosnesenkyi,
the western yellow faced bumblee. 

            Bumblebee moths exhibit a number of distinct variations on the Bombus theme, presumably to closer resemble locally abundant species. According to evolutionary theory, mimicry can only evolve to a certain level, beyond which mimics become so plentiful that sampling isn’t effectively discouraged.

            Moths are not born as flying insects, but develop in various stages, generally: egg, larvae, coccoon, pupae, adult. ,Bumblebee moth larvae are small green caterpillars of the “hornworm” type, which feed on snowberry, honeysuckle,
and dogbane, among others. Cocoons are formed on the ground from leaf litter.   

            One of the more pointless public debates that has resurfaced in recent years is that of creationism vs. evolution.  The creationist looks out upon the world, scratches his head, ponders all he sees, and declares: “God hath made it so.”  The evolutionist looks, scratches, ponders scientific evidence, and declares: “It’s evolution.”  A creationist treatment of H. diffinis, might be presented as follows:  “On the sixth day, about 4:30 or so, God said ‘Let there be a member of the hawk-moth family which acts like a hummingbird and looks like a bumblebee. Sweet.’”

            I caught up with a Bumblebee moth recently, who reluctantly agreed to slow down for a brief interview:

AW: Thanks for your time, I know you like to keep moving.

BBM: Try hovering under your own power next time you’re enjoying a meal.

AW: Which brings me to the first question.  Why the hummingbird act?

BBM:  Admittedly, the energy investment is large, but you can’t beat the handling and acceleration.  And while everyone else is looking for a place to park, we just zip right in and hover wherever we want.  And if trouble shows up, well, the motor’s still running, if you know what I mean. 

AW: And the bumblebee disguise?

BBM:  While many humans think nature is pretty, those of us who live there know what a warzone it can be.  Imagine being hunted every minute of the day!  Lots of moths go the camouflage route, but to me that seems so.. uninteresting.  We don’t mind looking conspicuous to predators because (laughs) we look like a stinging bumblebee!  And not a small one either.  It’s like robbing the bank by making a gun with your fingers in your pocket. 

AW: Unlike many moths, you are most active during the day.  Why is that?

BBM: Why go to all the trouble of impersonating two radically different life forms at once if it’s too dark for anyone to notice?  Besides, those night moths, they’re too edgy, have you seen the way they freak out over light bulbs?

AW: Once again, thank you, and best wishes for a good year.

BBM:  It’s the only one I got.  Peace out.

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