Wednesday, July 8, 2015

Phenology: Sphinx Moth

Not even a car pool but a paid driver failed to meet me this morning. I walked about two miles, noting the same cloudy weather and the same wildflowers mentioned yesterday, and considering not doing a phenology post today even if I found the time. We had just had one of those short showers of rain; the road was still wet.

Then I saw, lying beside the road, a rained-on Sphinx moth, intact but beginning to fade in the light and water. About that time a serious, soaking rain, which the land emphatically did not need, began to fall and continued for the whole time it took me to walk five more miles. Then I logged on to the hack writing site and found a nasty glitch impeding work there, which gave me time to find a few nice, informative, cheap-computer-friendly links about Sphinx moths for you.

Next to the Saturnids, the big silk moths, the Sphingids are the largest, easiest to recognize, and most interesting moth family. Unlike most Saturnids, the Sphingids have what can be called mouths--long sucking tubes, like butterflies' or bugs'--and drink liquids, usually flower nectar. Many of them rest with their long wings drawn back, forming a triangular shape, like giant flies or bees. Some of the smaller Sphingids seem to try to mimic flies or bees. Then there's a mid-sized family of Sphingids who have odd-shaped hind wings that look as if the back edges might have been cut out, and rest with their long forewings drawn back at an angle above their scalloped-looking hind wings. I've seen representatives of both of those families at the Cat Sanctuary from time to time.

What I saw this morning, however, belonged to the family of extra-large Sphingids, represented in North and South America mostly by the genus Manduca. Here are the cheap-computer-friendly Wikipedia pages for the two common and confusible species:

Note that, despite the Wikipedia writer's claim that M. sexta's caterpillars have straight markings like images of cigarettes and M. quinquemaculata's have V-shaped markings, the markings of all the specimens photographed look more like cigarettes than like V's. This is typical. The species commonly known by the names of their larvae, Tobacco and Tomato Hornworms, are consistently distinct species that don't crossbreed, but you have to examine them more closely than you probably want to look at them to know which species you're looking at. I've only ever found the caterpillars on tomato plants, but have suspected, based on descriptions, that most if not all the caterpillars I've found were Tobacco Hornworms.

Note also that one alternate genus name formerly proposed for these animals was Phlegethontia. Although Manduca don't have skull-shaped markings, this name pays tribute to a similar genus found in Europe, the dramatic-looking Acherontia that were featured in Silence of the Lambs and other works of fiction:

When moths are as big as a small woman's hand, may look solid black, may have black and gray or brown or beige markings that look (however vaguely) like skulls, squeak when frightened, and may even try to pretend they can bite or sting (even though they can't really), it's probably inevitable that people would call them names taken from ancient myths about the afterlife. As this web site mentioned recently, moths who enter houses or follow humans about are most likely trying to follow and/or summon other moths...although some Sphingids may also be attracted to sticky-sweet liquids.

The name that stuck to the big American Sphingids, however, has been Manduca, Latin for "glutton." All caterpillars spend almost all of their time stuffing themselves literally until they burst out of their skins. Large species can do a lot of damage to host plants. The big Sphingids happen to prefer plants that are toxic to most other creatures, which gives the sluggish, insensitive, slow-moving caterpillars what protection they have against predators. The horn at the back end is pure bluff for most species, rarely sharp or stiff enough to harm anybody...but just breathing the air near a caterpillar who's been eating tobacco is enough to kill some spiders. Humans can handle Sphingid caterpillars safely as long as we don't eat them.

Farmers might conceivably feel moved to celebrate some of the smaller Sphingids, some species of which are not pests and have interesting color patterns (often featuring pink and green), but nobody who's ever tried to raise tomatoes or potatoes feels inclined to celebrate the pests Manduca or Acherontia. For those who'd be more likely to observe National Moth Week, the week after next, if moth watchers were celebrating some harmless, pretty species like the Luna... may help if you understand that the hornworms are, in fact, general feeders. They can eat a huge variety of plants, and don't even necessarily need to eat leaves; they can eat grain too. They just prefer a diet of leaves reeking with toxic solanine. They could move off the tomatoes and eat the rest of the vegetables, too, but they almost never do.