Sphinx moth caterpillars are large, smooth-bodied caterpillars most easily recognized by a pointed horn or spine on their rear end. This horn, sitting on the last abdominal segment, is the single most reliable feature across the family. If you’ve found a fat, hairless caterpillar with a horn on its tail end, you’re almost certainly looking at a member of the Sphingidae family, commonly called hornworms or hawk moth caterpillars.
Features Shared by All Sphinx Caterpillars
Sphinx moth caterpillars share a body plan that’s distinct from most other caterpillar families. Their skin is smooth and free of the fuzzy, hair-like setae you’d find on woolly bears or tent caterpillars. The body surface has shallow wrinkles at each segment but is otherwise clean. Most species grow large, commonly reaching 3 to 3.5 inches long, and some exceed 4 inches. They’re thick-bodied and heavy enough to bend a small stem under their weight.
The caudal horn is the defining feature. It’s long, slender, and sits right on top of the final abdominal segment, pointing upward or slightly backward. It looks intimidating, but it’s pure bluff. Sphinx caterpillars do not bite or sting. They carry no venomous spines, no barbed hairs, and no chemical defenses you can touch. The horn is completely harmless. In some species, the horn is lost during the final molt before pupation, and in others (like the pandorus sphinx) it transforms into a small, eye-shaped button partway through the caterpillar’s growth.
Tomato vs. Tobacco Hornworm
These are the two sphinx caterpillars most gardeners encounter first, and they’re easy to confuse since both feed on tomato plants and look broadly similar: big, green, and horned. The differences come down to stripes and horn color.
- Tomato hornworm (Manduca quinquemaculata): Green body with eight white V-shaped markings along the back, pointing toward the head. The tail horn is black.
- Tobacco hornworm (Manduca sexta): Green body with seven diagonal white stripes bordered by black margins. The tail horn is orange-red.
Count the markings and check the horn color. Eight V-shapes with a black horn means tomato hornworm. Seven diagonal stripes with a red horn means tobacco hornworm. Despite the names, both species feed on tomatoes, peppers, and other plants in the nightshade family.
White-Lined Sphinx Caterpillar
The white-lined sphinx is one of the most common and most variable sphinx caterpillars in North America, which makes it both easy and tricky to identify. Every individual has the signature rear horn, typically yellow or orange, sometimes tipped in black. Beyond that, coloring varies dramatically.
The typical form in the Midwest is green (ranging from dark to lime green) with a series of black lengthwise stripes and rows of yellow, orange, or pink dots along the body. But western populations are often dull yellow or cream-colored, and dark forms can be brown to nearly black. The intensity and extent of stripes and spots shift from one caterpillar to the next, even among siblings. If you find a horned caterpillar with lengthwise (not diagonal) black stripes and colorful dots, especially on evening primrose, portulaca, or grape, the white-lined sphinx is a strong match. Fully grown larvae reach about 3.5 inches.
Pandorus Sphinx Caterpillar
The pandorus sphinx is one of the more visually striking species and goes through a notable transformation as it grows. Young caterpillars are green with a long, curved horn. Halfway through their development, the horn disappears entirely, replaced by an eye-shaped button on the rear segment. This button is a useful identification clue for later-stage caterpillars.
Color varies widely: green, pink, orange, light brown, dark brown, or nearly black. All color forms share a row of prominent white spots along each side of the body. Each spot surrounds a spiracle, which is a tiny breathing pore. If you find a large, hornless caterpillar with conspicuous white side spots and that distinctive eye button on the rear, it’s very likely a pandorus sphinx. These caterpillars feed primarily on grape and Virginia creeper.
Other Species Worth Knowing
Several other sphinx caterpillars turn up regularly in yards and gardens across North America, each with their own identifying details.
The achemon sphinx (also called the grapevine sphinx) feeds on both cultivated and wild grape leaves. Like the pandorus, it loses its horn during development. Fully grown caterpillars are 3 to 3.5 inches long and are rarely common enough to cause real damage to grapevines.
The blind-eyed sphinx caterpillar is yellow-green with dense white speckling, six oblique yellow lines running from segments one through six, and white spiracles rimmed in black. An additional yellow line extends from the base of the sixth abdominal proleg up to the dorsal horn. Its overall appearance is pale and finely textured compared to the bolder markings of hornworms.
The one-eyed sphinx caterpillar is green with white speckles and oblique yellow stripes above the spiracles, plus a prominent white stripe running to the tip of a purple horn. That purple horn color is a quick giveaway if you spot it.
How to Narrow Down Your Caterpillar
When trying to identify a sphinx caterpillar, work through these features in order:
- Horn present or absent: A horn confirms it’s likely a sphinx. If there’s no horn but there’s an eye-shaped button on the rear, it may be a later-stage pandorus or achemon sphinx.
- Horn color: Black, red, orange, yellow, or purple. This alone can separate common species.
- Stripe direction: Diagonal (oblique) stripes versus lengthwise stripes versus V-shaped markings. Diagonal stripes are most common in the family, but the pattern varies by species.
- Stripe and spot count: Count the stripes or markings. Seven versus eight diagonal markings is the difference between tobacco and tomato hornworms.
- Body color: Green is most common, but brown, black, pink, and cream forms exist in several species.
- Host plant: What the caterpillar is eating narrows the options significantly. Tomato or pepper plants point to hornworms. Grape or Virginia creeper suggest pandorus or achemon sphinx. Evening primrose and portulaca suggest white-lined sphinx.
What Happens After You Find One
Sphinx caterpillars spend their entire larval life eating foliage, growing through several molts over a few weeks. The body color often shifts between early and late stages, sometimes changing enough to look like a different species. In some species, the upper surface turns light reddish-brown just before the caterpillar is ready to pupate.
When fully grown, the caterpillar crawls down from its host plant and burrows into the soil. It tunnels in, creates a small cavity underground, and pupates there without spinning a silk cocoon. The pupa is dark brown, tapered at both ends, and roughly the size of a short cigar. In species with a long tongue as adults, the mouthparts form a visible loop on the underside of the pupa. The last generation of the season overwinters underground as pupae, with adults emerging the following spring or summer.
If you spot tiny white cocoons stuck to the outside of a sphinx caterpillar, those belong to parasitic wasps, not the caterpillar itself. The wasp larvae develop inside the hornworm, then chew their way out and spin small cocoons fastened to the caterpillar’s skin. A parasitized caterpillar will stop feeding and die, so gardeners who find these typically leave them alone to let the wasps complete their cycle, since those wasps will go on to parasitize more hornworms.