Black witch moth makes very rare visit to Martha's Vineyard
Photo by Matt Pelikan
Ordinarily the tail end of the Vineyard's season for Lepidoptera (that is, for butterflies and moths), the end of October brought this year's most unusual Lepidopteran find. While working in a garden near Black Point Pond on Tuesday, alert Vineyard Haven resident Andrew Jephcote discovered and identified a black witch moth (Ascalapha odorata).
This massive moth (the one Mr. Jephcote found was more than six inches across) normally inhabits the tropics, ranging from Brazil to the Caribbean and southernmost Florida and Texas. But the species has a well-documented tendency toward long-distance migration, dispersing northward in late summer and fall. There are reportedly records of this moth from all 50 states, and, on the East Coast, from as far north as Newfoundland. Interestingly, a second black witch was found in Hyannis three days after Mr. Jephcote discovered his.
Still, black witches occur only rarely this far from the core of their range, and Mr. Jephcote's find appears to be, quite literally, a once-in-a-century event. Asked about the moth, Dr. Paul Goldstein, an entomologist and part-time Vineyarder who is the leading expert on our Lepidoptera, was aware of only one previous Island record for this species: William Place, an obscure but energetic observer from the early 20th century, published a report in an entomology journal in 1909.
Mr. Jephcote's moth is a striking insect, intricately patterned in funereal tones ("Paisley," said one of my friends on viewing a picture). Compared to native silk moths like the polyphemus and cecropia, which rival it in size, the black witch seemed to me to have stiffer wings and a much more aerodynamic shape. It also possesses a proboscis, a straw-like organ butterflies and some moths use to drink nectar or other fluids. Many silk moths, in contrast, lack fully developed mouth parts and are incapable of eating as adults.
With the possibility of refueling, and equipped with long, pointed wings driven by powerful flight muscles, this species is clearly well adapted to long-distance flight. But in all probability the insect's trip to the Vineyard was aided by the relatively mild weather and persistent southwesterly winds that characterized much of October. The ability of even a large moth to travel from the tropics to our latitude depends on a favorable convergence of flying ability, weather, and timing.
Such dramatic dispersal seems like a foolish strategy for a tropical insect. Alone on the Island, this moth (which is a male) has virtually no chance of finding a female to mate with. Even if it could, there would be no plants suitable for their offspring to eat. And even if there were, the onset of winter would kill any larvae before they could mature.
But if its journey was a reproductive dead end for this individual moth, a penchant for long-distance vagrancy is fairly common among moths and (especially) butterflies. While most dispersing moths are buying a one-way ticket to oblivion, a few individuals may wind up in suitable habitat, establish a new population, and thereby extend the range of the species.
So vagrancy is a strategy that sacrifices some individuals in order to create new opportunities for the species as a whole. The urge and ability to travel may give species like the black witch an advantage in the face of global warming, enhancing their ability to shift distribution as the climate changes. Dr. Goldstein speculates that visits from this moth may gradually grow more frequent in coming decades, as its core range moves farther north and longer, milder autumns facilitate northward dispersal.
Despite its beauty and remarkable ability to travel, the black witch (as its name suggests) has acquired a shady reputation in parts of the tropics. In many cultures, the moth is associated with death and dying, and it is viewed either as an ill omen or as a restless spirit.
For me, though, Mr. Jephcote's discovery has a strictly positive ring, illustrating both the remarkable capabilities of insects and the Vineyard's role in supporting the migration of wildlife across the hemisphere.