Agrius cingulata, Dallas, Collin County, Texas,
October 8, 2010, courtesy of Robert McClure.
sweet potato, pool side, Dallas, Collin County, Texas,
October 16, 2010, courtesy of Robert McClure.
It is possible that the larva did indeed feed on the lush foliage of the sweet potato vines earlier in the summer. It is also possible that the moth flew in from a more remote locale. The adult moths fly and feed at night, nectaring from flowers that remain open after dark.
Almost all moths are attracted to lights, and the light coming from inside the house or a night light from near the window screen probably lured the moth to its perch.
If you have a combination of adult nectar sources and larval food plants, you will probably attract a great variety of Sphingidae. Many of these adult moths are especially attracted to moon flowers and phlox which provide nectar at night. Larvae of some local Texas species species feed on tomato and pepper foliage, others on mint or sage (Lintneria species), some on pentas (Xylophanes tersa), some on lilac, passionflower, honeysuckle, juniper, grape, Virginia creeper (Eumorpha species), portulaca, primrose, fuschia, etc., all of which are often planted in yards for their produce or appearance.
Some of the day flyers, (Hemaris, species are especially fond of nectaring from butterfly bush.
Sometimes the larvae are regarded as pests, as they can reach considerable size and consume large amounts of foliage. The tomato feeders (Manduca sexta, Manduca quinquemaculatus) can make a mess of your tomato plants, and once all the foliage is gone, they have been known to munch on the green fruit. So be careful what you plan for.
Larvae of most Sphingidae species have an anal horn which looks menacing, but I do not know of any North American Sphingidae species whose larvae pose any kind of threat to humans, other than the distress of seeing your plant foliage disappear!
Just by coincidence, on October 16, 2010, David Bygott provided me with a beautiful image of an Agrius cingulata larva that I had identified for him. It is quite remarkable how these larvae are well camouflaged in the foliage upon which they feed.
In this case the brown subdorsal line on the larva is almost the same colour and thickness as the foliage stem. The green colouration of the larva is probably a good match for the foliage, and the dark, oblique lines on the larva's side, probably match the angle at which branches or leaf stems would emanate from the main stem.
This larva can exceed four inches in length. In most cases, the lush, abundant foliage of the sweet potato vine keeps it both well fed and hidden.
Agrius cingulata green form (there is also a brown form), courtesy of David Bygott.
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