Achemon sphinx moths’ range in U.S. is shrinking
While watering my rock garden, I inadvertently flushed an Achemon sphinx moth, Eumorpha achemon, which flew less than 20 feet to clutch onto a Stella D’oro lily, where it stayed for the remainder of the day.
This species is crepuscular and nocturnal, so it is rarely seen during the day but first appears about dusk and is active most of the night. Achemon sphinx moths are the smallest in the genus Eumorpha, but are large in comparison to moths in general. They have a body length of up to 2 inches and wingspans from 3.4 to 3.8 inches.
On the dorsal side, adult moths have soft brown tinged with pink and dark brown triangular patches on the thorax next to the wings. The bright salmon colors of the hindwings flash when the moth flutters.
Five instars or stages of caterpillars change colors dramatically as they molt. The first stage is light yellow, with a very prominent horn, which earns the sphinx caterpillars the common name “hornworms.”
Second-stage caterpillars are either green or brown, while third and fourth stages are green or brown with seven white diagonal stripes on each side. Fifth-stage caterpillars are red or brown or green and lack the horn, but a conspicuous eye spot appears where the horn was attached.
The puparium is about 3 inches long, dark brown and rounded at one end, pointed at the other. It is rare to find a puparium, for they are usually buried in the soil beneath the plants that the caterpillars fed on.
Caterpillars eat the leaves of many species in the family Vitaceae, which contains species of grapes and Virginia creeper. For this reason, vintners do not welcome Achemon sphinx moths to their vineyards.
Sphinx moths have a number of traits usually described with superlatives. They are strong and fast fliers — top speed is 30 mph, and males have been documented to fly over 2 miles to find a mate. Their wings beat so fast that they emit a fluttering buzz — wingbeat frequencies during acceleration reach 41 cycles (up and down) per second.
Sphinx moths can hover, an ability shared only with hummingbirds, hoverflies and some bats. Their color vision is acute, allowing them to distinguish flower colors at light levels that appear pitch black to you and me. Odor sensors on their antennae are incredibly sensitive, allowing males to find fragrant flowers at night and to detect a plume of female pheromone being released more than a mile away.
A species of sphinx moth native to Madagascar has a tongue 14 inches long to reach nectar in the extremely long spurs of star orchids. They can hear the bat sonar and can mimic it to confuse the threatening bat. No doubt about it, sphinx moths are extraordinary.
About 1,450 species of sphinx moths have been described worldwide and more than two dozen are native to Colorado. The most common sphinx moth in Colorado is the white-lined sphinx, Hyles lineata.
Both Achemon and white-lined sphinx moths have enormous ranges, spanning most of the North American continent. High abundance and a large geographic range usually indicate that the species is secure. But a disturbing trend has been documented in the eastern portions of the ranges.
Sphinx moths have been declining for the last 50 years in New England. Biologists have been documenting this ongoing ominous trend, and trying to determine which factors are driving it. Habitat destruction, coastal development, overgrazing by deer and other factors have been discussed, but David L. Wagner, at the University of Connecticut, has built a convincing case that sphinx declines are attributable to Compsilura concinnata, a parasitic, tachinid fly introduced from Europe to New England in 1906 to control two introduced pests, gypsy moths and brownttail tussock moths.
Unfortunately, C. concinnata is a generalist, laying its eggs on caterpillars of over 200 species in North America. When the eggs hatch, larvae burrow into the caterpillar to consume it from the inside — a grisly demise. Wagner has compiled data documenting the decline of sphinx species in New England, and he is unable to find evidence that either Achamon or white-lined sphinxes still live in Connecticut.
A neighbor gave me an Achemon puparium found among the roots of a lilac tree, and we agreed that I would try to photograph the moth as it emerged. However, it never emerged, and when I opened it to see what was wrong, I found that it was completely filled by numerous puparia of a tachinid fly (identified by Valerie Mckenzie). We have several native tachinid flies in Colorado, but I was troubled by the possibility that the tachinid fly that probably drove Achemon and whitelined sphinxes to local extinction in Connecticut had arrived in Colorado.
Well-intentioned biologists have introduced C. concinnata in many other places beyond New England, including Minnesota and California. Fortunately, Wagner informed me that it has not yet appeared in the southern Rocky Mountains. Extinction is forever, and it would be tragic to lose such a remarkable group of moths.