The sphinx, or hawk, moths are relatively heavy- bodied and are strong fliers. Some are important pollinators of trees and shrubs, especially those having white or light- colored flowers. Most sphinx moths fly at night, so we may not see them except as they are attracting to lights outside the home. The clearwing moths, such as the snowberry and hummingbird, do fly during the day and are common visitors to home gardens.
Just as the adults are large- bodied and heavy set, the sphinx caterpillars can also become quite the behemoths when compared to other caterpillars common to New England. They usually have a conspicuous horn on the hind end, but some species start off with a horn and end up with a “ button “ ornament instead. Most of these caterpillars feed on trees and shrubs, but some, such as the tobacco and tomato hornworms and the hermit sphinx feed on nightshades or basil respectively. Because of their size, damage to host plants can be substantial as they approach the final instars.
If you want to find hornworms, knowing the host plants is the first step. Many species can be found on grape and Virginia creeper. These include the hog ( or Virginia Creeper Sphinx ), the Pandorus sphinx, Abbot’ sphinx and the Achemon sphinx. Look underneath leaves where feeding is evident, then look for leaf stems left behind as caterpillars get larger and move toward inward leaves. If tomato leaves are disappearing, the Tobacco hornworm may be lurking nearby. Although this caterpillar gets huge, it can be surprisingly difficult to see as its color blends in with tomato foliage and stems. The final instar can eat you out of house and home in no time. I once raised one from an egg found on nightshade and it grew to the size of an Oscar Mayer hot dog. Fecal pellets are another indicator of caterpillar feeding, and the sphinx variety are elongate and have six deep grooves and may be quite large as caterpillars approach the penultimate and final instars. Eggs are usually laid on the undersides of leaves and are large and spherical. A large, green spherical egg found on a tomato leaf is most likely that of the tobacco hornworm. If you are not interested in raising this caterpillar, crush the egg and future feeding damage can be avoided.
Blueberry or huckleberry are the host plants of the fabulous Huckleberry Sphinx. When small, its horn is striped with lemon yellow and raspberry red ( one color short of Trix™ ). Its body is granulose, looking like it has been sprinkled with large crystals of sugar. As it matures, raspberry markings develop on its sides and back. Last year I found several of these on both host plants and at various locations. Each year is different, though, and abundance or apparent scarcity of species fluctuates accordingly.
When at rest or when disturbed, sphinx caterpillars position themselves in a posture that reminds me of a seahorse. Some thrash from side to side and some may regurgitate a green fluid as well. Some actually will nip, and Abbot’s sphinx and Walnut sphinx caterpillars make sounds when threatened. All these means are probably very effective at dissuading birds, but predatory wasps seem to be able to get past all that behavior. When you find a caterpillar with cocoons all over it, the internal feeding of cotesia or braconid wasps has been completed and the caterpillar is doomed to die a slow death. It is unfortunate that many introduced parasites that were meant to control pest caterpillars are now decimating benign native species, but that is just a sad story of good intensions backfiring.
If you raise sphinx caterpillars, make sure that final instars have a suitable pupating medium, such as abundant mulch, plant litter or soil. Or simply release onto a host plant and let nature take its course. Caterpillars tend to be sedentary more than mobile and they have a good gripping ability which makes them easy to transfer to fresh food material. Keep pupa moist over winter and provide air to containers to keep from developing mold. Be vigilant and release as they eclose. Moths emerging in small containers may not be able to expand wings fully, and will be doomed as wings will harden deformed.
Sphinx caterpillars are very commonly seen in the fall as they travel over lawns, driveways and paths on their way to pupate. If you see them, just remove them to a safer spot and they will find their way to a good spot to pupate for the winter.
Pamm Cooper All Photos© 2014 Pamm Cooper