Hawk Moth Caterpillar Identification: Horns, Stripes, Eyes

A hawk moth caterpillar is a large, stout, smooth caterpillar with a horn sticking up from its rear end; if you see that horn, you are almost certainly looking at the family Sphingidae. Wikipedia describes the larvae as medium to large with stout bodies and five pairs of prolegs, and notes that most carry the horn, which is why they are called hornworms.

Three cautions:

• The horn can vanish. In some species it is reduced or absent in the last stage (Wikipedia), and the small elephant hawk-moth has none at all (Woodland Trust).
• Colour can change. The elephant hawk-moth caterpillar comes in brown and bright green forms (Woodland Trust).
• Diagonal stripes and eyespots help. Several species have slanting side stripes; the elephant hawk-moths have large eyespots near the head.

From the Woodland Trust's identification guide. Lengths are maximums.

• Elephant hawk-moth (*Deilephila elpenor*): brown or bright green, four large eyespots and a small stubby tail horn; up to 80 mm; July to September on willowherbs, fuchsias, Himalayan balsam, bedstraws and enchanter's nightshade.
• Small elephant hawk-moth (*Deilephila porcellus*): like the elephant but with no tail horn and eyespots with reddish centres; up to 60 mm; July to September on bedstraws and rosebay willowherb.
• Poplar hawk-moth (*Laothoe populi*): light green or yellowish-green with dense yellow speckles, pale yellow stripes and a yellow tail horn, some with pinkish-red blotches; up to 70 mm; July to September on poplars, aspen, willows and sallows.
• Privet hawk-moth (*Sphinx ligustri*): bright green with white and purple diagonal stripes, a curved black-tipped horn and a dark ring around the head; up to 85 mm, the largest here; June to August on privet, ash, lilac, honeysuckle, holly, guelder rose and garden plants.
• Lime hawk-moth (*Mimas tiliae*): greyish-pink when mature, with a tail horn that is blue on top and often red and yellow underneath; up to 65 mm; July to September on limes, birch, elm, alder and London plane.
• Eyed hawk-moth (*Smerinthus ocellata*): green with white diagonal stripes, a bluish horn and a bright yellow collar around a flat, triangular head; up to 75 mm; June to September on willows, sallows, apple, aspen and poplar.
• Pine hawk-moth (*Sphinx pinastri*): dark green with a brown stripe down the back, broken cream lines on the sides, a brown head and black horn; up to 80 mm; July to September on Scots pine, other pines and spruces.
• Hummingbird hawk-moth (*Macroglossum stellatarum*): mostly green with a thick creamy-yellow side stripe, a white line above it and a black and yellow-tipped horn; up to 55 mm; mainly July to August on bedstraws and wild madder.

The two big green hornworms on tomatoes are told apart by their side stripes. UC IPM says the tobacco hornworm has seven diagonal stripes on each side, while the tomato hornworm has eight chevron-shaped stripes. University of Minnesota Extension describes the tomato hornworm's marks as eight white V shapes on each side, with a black horn on the last abdominal segment, and says hornworms can reach four inches, among the largest caterpillars in Minnesota. Young tomato hornworms are yellow to white with no markings.

Both become sphinx moths: large, heavy-bodied, mottled grey-brown moths with yellow spots on the sides of the abdomen and a wingspread of four to five inches (University of Minnesota Extension). UC IPM gives the development time as about two months in summer, with larvae feeding for three to four weeks, then pupating in the soil; the winter is passed as a pupa, and most areas have two generations a year.

The horn is the part people worry about, and the Woodland Trust says it is soft and harmless, possibly acting as a decoy for hungry predators. Hawk moth caterpillars have no spines or stinging hairs, and none appears on the University of Kentucky's list of stinging caterpillars. That is not a reason to eat one or to let a pet chew it. If anyone reacts after handling any caterpillar, wash the skin and, in the US, call Poison Help on 1-800-222-1222. The caterpillars that do sting are on the poisonous caterpillar page.

Mostly good. Adult hawk moths are strong pollinators: Wikipedia notes that their proboscis ranges from 1 cm up to 28 cm long, which lets them reach nectar in flowers with long tubes that other pollinators cannot, and that some species hover while they feed. The UK caterpillars above feed on plants such as willowherb, bedstraw, poplar, willow and lime.

The exception is the tomato hornworm in vegetable gardens. University of Minnesota Extension says hornworms can quickly defoliate plants, and the last caterpillar stage eats nearly as much as all the earlier stages combined. Its advice is to pick them off by hand, and to leave any hornworm carrying white, rice-like cocoons: those are braconid wasps, which kill the hornworm when they emerge.

Some are common. Butterfly Conservation lists the elephant hawk-moth as common, very widely distributed in England and Wales, widely in Ireland and thinly in Scotland, flying from May to July in one generation. The hummingbird hawk-moth migrates to the UK from southern Europe each year and can be seen hovering over flowers (Wildlife Trusts); the Woodland Trust notes it cannot survive cold winters there.

The caterpillars are easiest to find between June or July and September, the seasons the Woodland Trust gives for the UK species, and fully grown ones leave their plants to pupate in the soil (Wikipedia).

Take one photo from the side, so the stripes and the horn show, and one from the front for eyespots and the collar behind the head. Include the plant, because food plant helps separate look-alikes such as the eyed and poplar hawk-moths. Photograph it and InsectLens identifies it; then compare with the lists above. If you move a caterpillar off a path, put it on the same kind of plant.

Research and drafting for this page used AI assistance. Every figure, date and quotation was then checked line by line against the sources listed at the bottom of the page, each of which was opened while writing. Nothing here is a diagnosis. If a bite, sting or contact with an insect is followed by trouble breathing, swelling of the face or throat, spreading redness, fever or any symptom that worries you, get medical care; in the United States Poison Help (1-800-222-1222) is free, confidential and open 24 hours a day.