On this page
How to identify it
- Large caterpillars are green with eight white V-shaped marks along each side and a horn on the last body segment. Minnesota and Clemson describe the horn as black; Colorado State calls it dark green with black sides.[1][4][5][6]
- Small caterpillars are yellow to white with no markings. Darker forms of grown caterpillars exist but are less common.[1][7][6]
- Dark green or black droppings on leaves or on the ground under plants are often the first sign, since the green caterpillars blend in with the foliage.[1][2]
- Eggs are smooth and round, about 1/16 inch across, light green at first and turning white before they hatch.[4][5]
- The adult is a large, heavy-bodied gray-brown moth with a wingspan of 4 to 5 inches and five yellow spots along each side of the abdomen.[1][7][3]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Tobacco hornworm (Manduca sexta) | Has seven diagonal white lines instead of V-shaped marks and a red, usually curved horn. Colorado State says it is the more common of the two in Colorado gardens and east of the Rockies, and Clemson says its range runs from southern Canada to Argentina, while the tomato hornworm's ends in the southern United States.[7][6][4][8] |
| Hummingbirds (the adult moths) | Hornworm moths are often mistaken for hummingbirds as they hover over flowers. Colorado State notes the moths most often called hummingbird moths are other sphinx moths, chiefly the whitelined sphinx.[7][3][6] |
Where it lives
A garden pest from Minnesota and Colorado to California; adults fly long distances and can migrate into northern areas from the south.[1][7][2]
Biology and life cycle
Hornworms spend the winter as pupae in the soil. Moths emerge from late spring into summer: Colorado State gives late May and June, Clemson early June to as late as August, and Wisconsin late June.[1][2][6][4][3]
Females lay eggs singly on leaves; Clemson says they lay at night, one to five eggs per plant visit, and that eggs hatch in about four days depending on temperature.[2][8][4]
Caterpillars feed for about three to four weeks (Clemson says three, Wisconsin and Colorado State about a month), then drop off the plant and burrow into the soil to pupate.[1][8][4][3][7]
There are usually two generations a year, with a second round of caterpillars in mid to late summer. Colorado State says the second generation is mainly a feature of southern areas and warm summers, and Clemson says at least two occur each year in South Carolina.[8][1][3][7][4]
Besides tomato, they feed on potato, eggplant, pepper and tobacco, and on weeds such as horsenettle, jimsonweed and nightshade.[1][4][5]
Tomato and tobacco hornworms often occur together and are attacked by the same parasitic wasp. In heat experiments, the tomato hornworm grew faster and larger than the tobacco hornworm at high temperatures, and extreme heat killed the developing wasps but not the caterpillars.[9]
Damage and signs
- Caterpillars eat entire leaves and small stems, starting near the top of the plant, and chew large pieces out of green fruit. They feed on the fruit surface, leaving large open scars, rather than boring in.[1][2][4][5]
- The last caterpillar stage eats nearly as much as all the younger stages combined. Wisconsin says larvae can eat up to four times their weight in leaves and fruit each day, and Iowa State says full-grown caterpillars seem to eat about a leaf an hour.[1][3][10]
- Damaged fruit often rots on the vine or is left with dry feeding scars, though leaf loss is much more common than fruit damage.[3][4][5]
- Only the caterpillar stage causes damage, and it is usually worst in midsummer and in warm inland areas. The adult moths feed on nectar and do not harm plants.[2][3]
- Penn State notes hornworms are especially attracted to plants under drought stress.[5]
Health risk
Hornworms are plant pests: the caterpillar is the only stage that causes damage, and the moths feed on nectar. Iowa State notes the caterpillars won't hurt you when you pick them off.[2][3][10]
Control
Sanitation
Remove weeds where moths lay eggs, and till the soil after harvest to destroy pupae; Wisconsin says tillage can kill up to 90% of larvae in the soil.[1][2][3]
Traps and physical control
Handpicking is the most effective control: check plants at least twice a week in summer and drop caterpillars into soapy water or snip them with shears.[1][2][3][4]
Search at dusk or dawn, when caterpillars feed on the outside of the plant and are easier to see.[7][6]
Biological control
Lady beetles, lacewings, paper wasps, Trichogramma egg parasites and parasitic wasps all attack hornworms and normally keep numbers down.[1][2][3]
Pesticides
Bacillus thuringiensis (Bt) or spinosad work best on young, small caterpillars and should be applied before defoliation is severe.[1][2][10]
Wisconsin says hornworms rarely do enough damage to need insecticides in home gardens. Broad-spectrum products such as pyrethroids (bifenthrin, permethrin) or carbaryl also kill beneficial insects; check the label for days to wait before harvest.[3][1][6]
Hornworms covered in white cocoons
A small braconid wasp, Cotesia congregata, lays its eggs in or on hornworms, and the wasp larvae feed inside the caterpillar.[1][4][5][3][9]
The wasp larvae then spin cocoons on the hornworm's back that look like grains of white rice.[1][5][4]
Leave these hornworms in the garden. A parasitized hornworm has stopped feeding, and the wasps that emerge go on to parasitize other hornworms.[1][4][5][3]
Where sources disagree
Horn color: Minnesota calls the tomato hornworm's horn black and Clemson straight and black, while Colorado State describes it as dark green with black sides. Iowa State says only that the horn is red or green depending on the species, and Wisconsin red or black.[1][4][6][10][3]
Side markings: most sources describe eight V-shaped or chevron marks, but Wisconsin describes them as eight diagonal white stripes.[1][8][4][3]
Size: Minnesota, UC IPM and Wisconsin give up to 4 inches, Clemson 3 to 3 1/2 inches, Penn State about three, and Iowa State 4 to 5 inches.[1][2][3][4][5][10]
Where eggs go: Clemson and Wisconsin say the undersides of leaves, Colorado State the upper surface, and Minnesota both.[4][3][7][1]
Seeing the moths: Colorado State's IPM page and Wisconsin say they are often mistaken for hummingbirds at flowers, but Colorado State's Extension fact sheet says tomato hornworm moths fly after dusk and are rarely seen except at porch lights.[7][3][6]
Common questions
- Is it a tomato hornworm or a tobacco hornworm?
- Look at the side markings and horn: eight V-shaped marks mean tomato hornworm; seven diagonal lines and a red, usually curved horn mean tobacco hornworm.[4][7][8]
- What are the white things stuck to a hornworm?
- They are cocoons of a parasitic wasp. The hornworm has already stopped feeding, so leave it alone and let the wasps emerge to parasitize more hornworms.[1][4]
- Will Bt kill a big hornworm?
- Bt works best on very young caterpillars, and small ones are easier to treat than large ones; big hornworms are easy to spot and handpick.[1][2]
Sources
- University of Minnesota Extension, “Tomato Hornworms.” extension.umn.edu/yard-and-garden-insects/tomato-hornworms (accessed 2026-11-11)
- University of California Statewide IPM Program, “Hornworms (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/hornworms/ (accessed 2026-11-11)
- University of Wisconsin-Madison Extension, “Hornworms (XHT1107).” hort.extension.wisc.edu/articles/hornworms/ (accessed 2026-11-11)
- Clemson Cooperative Extension Home & Garden Information Center, “Tomato Insect Pests (HGIC 2218).” hgic.clemson.edu/factsheet/tomato-insect-pests/ (accessed 2026-11-11)
- Penn State Extension, “Tomato Insect Pests in the Home Garden.” extension.psu.edu/tomato-insect-pests-in-the-home-garden (accessed 2026-11-11)
- Colorado State University Extension, “Hornworms and 'Hummingbird' Moths (Fact Sheet 5.517).” extension.colostate.edu/resource/hornworms-and-hummingbird-moths/ (accessed 2026-11-11)
- Colorado State University, College of Agricultural Sciences, “Hornworms (IPM Pests).” agsci.colostate.edu/agbio/ipm-pests/hornworms/ (accessed 2026-11-11)
- University of California Statewide IPM Program, “Tomato Pest Management Guidelines: Hornworms.” ipm.ucanr.edu/agriculture/tomato/hornworms/ (accessed 2026-11-11)
- Journal of Experimental Biology, via PubMed, “Malinski, Sorenson, Moore, Willett and Kingsolver (2023), Host species differences in the thermal mismatch of host-parasitoid interactions.” pubmed.ncbi.nlm.nih.gov/37338185/ (accessed 2026-11-11)
- Iowa State University Extension and Outreach, “Tomato Hornworm (Yard and Garden).” yardandgarden.extension.iastate.edu/encyclopedia/tomato-hornworm (accessed 2026-11-11)
- iNaturalist, “Manduca quinquemaculatus taxon page (order and family).” www.inaturalist.org/taxa/224420 (accessed 2026-10-06)