The smallest hornworm I’ve ever seen was about an inch long, but within a few weeks, they’ll grow to about a quarter inch wide and up to 5 inches long. However, large numbers of larvae can sporadically occur in home gardens. Although we call them worms, tomato hornworms are actually caterpillars of the five-spotted hawk moth (Manduca quinquemaculata). This could be a great learning opportunity for your kids! The moths tend to be active in the early evening feeding on nectar of several fragrant flowers. With all products, treatments should be applied when larvae are still in the early instars. Only leaf-eating caterpillars are affected by the Bt. However, larvae will also attack eggplant, pepper, and potato. And come back every day to check again. Companion planting with flowers to repel hornworms is worth a try. A black projection or "horn" on the last abdominal segment gives the caterpillar the name "hornworm.". The eggs hatch in six to eight days and are oval, smooth, light green to yellow in color, and measure 0.10 cm in diameter. Try planting borage, basil, marigolds, alyssum, or wildflowers with your tomato plants. A black "horn" projects from the rear of the caterpillar. Tomato hornworm moths are large, furry, brown to grey colored moths with a wingspan up to 8 inches! Small tomato hornworms are yellow to white in color with no markings. This insect does not typically reach economically damaging levels on commercial farms. They lay their small, translucent green eggs on the undersides of leaves of tomato plants and other hosts. This insect does not typically reach economically damaging levels on commercial farms. If you are having a lot of trouble with hornworms and other caterpillars, you might consider alternating Bt and spinosad treatments during the months that caterpillars are most active. After a few days, the eggs hatch releasing small caterpillars who immediately begin munching on the leaves of your tomato plants. The tomato hornworm, Manduca quinquemaculata (Lepidoptera: Sphingidae), is native to the United states, and is commonly found throughout the northern states. Moths emerge from the soil, mate, and then begin to deposit the eggs of the next generation on tomato plants. Have you ever walked out to your garden one morning to find your tomato plants suddenly stripped bare of their leaves and flowers? In late spring and summer, fully grown hornworms burrow into the soil around your tomato plants where they pupate and overwinter in the soil around the base of your plants. Their presence indicates that you have a healthy insect population and the affected hornworm will die before it can damage your plants too much. Here is a great resource for teaching about life cycles using the tomato hornworm. Tobacco hornworm image sourced from Whitney Cranshaw, Colorado State University, The moth is a mottled gray-brown color with yellow spots on the sides of the abdomen and a wing spread of 4 to 5 inches. And, if you ask me, a hornworm eating your tomato plants is a tomato hornworm. Spinosad is a natural substance made by bacteria that live in the soil. Within about 30 days, the caterpillar has finished growing at which point it will bury itself in the soil around the base of your plant to pupate. Home » Gardening » Growing Tomatoes » Get Rid Of Tomato Hornworms (Without Toxic Chemicals). Tomato hornworm blends in with green leaves. The white eggs are actually wasp larvae that are feeding on the hornworm. Characteristically they sport a flexible spine (“horn”) on the hind end, although in some species this is lost and replaced with an eyespot marking. (The related tobacco hornworm is similar but has seven white stripes down the side and a red horn.) The Minn. Extension IPM Program is a collaboration of University of Minnesota Extension & the College of Food, Agriculture, and Natural Resource Sciences (CFANS). One of the most common is a small braconid wasp, Cotesia congregatus. Department of Entomology1980 Folwell Avenue | St. Paul, MN 55108-6074(612) 624-3670 | contact Bill Hutchison They also have an impressively long proboscis which makes them uniquely suited to feeding on trumpet-shaped flowers like honeysuckle. & R.A. Metcalf. New York. After mating, females deposit oval, smooth, light green eggs on lower and upper leaf surfaces. of Minn.). Academic Press. (Hymenoptera: Vespidae). Handpicking the hornworms from infested plants is a safe and effective option in smaller plantings. Cranshaw, W.S. As the larvae mature in size the amount of defoliation increases, with the last instar consuming over 90% of the total combined foliage consumed by all instars. Gardeners should also watch for parasitic wasp activity. This insect does not typically reach economically damaging levels on commercial farms. Metcalf, R.L. 1993. Handbook of Vegetable Pests. This common wasp kills and feeds upon a large proportion of the larvae, and will also attack cabbage looper and other garden caterpillars. It affects insects that eat or touch it by disrupting their nervous system leading to death in one to two days. Hutchison Department of Entomology, University of Minnesota. When you find a hornworm caterpillar, the best thing you can do is pick it off your plant and step on it or feed it to your chickens. Tomato hornworms are large creatures compared to tiny pests like aphids and whiteflies. Looking for the culprit you see an enormous alien-looking green caterpillar with white stripes and red dots down its back. Tomato hornworms can strip a plant down to its bones overnight with their voracious appetites. There are usually 2 generations of this insect each year in the upper Midwest. Hard to say without a pic. During July and August they also occasionally feed on the tomato fruits. Hornworms can’t hurt you but they’re little legs are super grippy and can pinch a little. This post contains affiliate links. The caterpillar reaches the final instar in 3-4 weeks, and is 3 1/2 to 4 inches when fully mature. Those are more common on my tomato plants. The adult moth, sometimes referred to as a "sphinx", "hawk", or "hummingbird" moth, is a large, heavy-bodied moth with narrow front wings. They’re easy to distinguish by their striping and color of their horn. They have a horn that sticks up off their rear end, and a stubby green face with pointy claws for shoving food into their little mouths. Tillage has shown to cause up to 90% mortality. Be careful using spinosad around pollinators and other beneficial insects. Wold-Burkness & W.D. Overly concentrated solutions can harm the leaves and fruit on your plants. Eggs of the tomato hornworm are deposited singly on both the lower and upper surface of leaves in late spring. In many instances, hand picking is an adequate method of controlling damage from hornworm problems. Current Guidelines for Pesticide Plant-Back Restrictions, Midwest Vegetable Production Guide for Commercial Growers 2020,,,