Hornworms feed almost exclusively on plants in the nightshade family, Solanaceae. That means tomatoes, tobacco, peppers, eggplant, potatoes, and several wild relatives are their primary targets. The two species most gardeners encounter in North America are the tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquemaculata), and despite their common names, both will happily devour tomato plants. Their loyalty to the nightshade family is strong but not absolute, and the reasons they stick to these particular plants, along with the surprising exceptions, reveal a lot about how these caterpillars experience their world.
The Core Menu: Nightshade Family Plants
If you grow anything in the Solanaceae family, hornworms consider it a potential meal. The list of confirmed host plants is long, but the most commonly attacked crops and wild plants include:
- Tobacco (Nicotiana tabacum) and wild tobacco species
- Tomato (Solanum lycopersicum)
- Potato (Solanum tuberosum)
- Eggplant (Solanum melongena)
- Pepper (Capsicum species)
- Jimson weed (Datura stramonium) and other Datura species
- Ground cherry (Physalis species)
Field studies in Kentucky documented tobacco hornworm eggs and larvae on tobacco, jimson weed, tomato, and potato throughout the growing season, confirming that these are not just laboratory curiosities but genuine field hosts.1Oxford Academic. Seasonal Parasitism and Predation of Eggs of the Tobacco Hornworm on Various Host Plants in Kentucky Among wild plants, jimson weed and other Datura species are especially important hosts. In areas where tobacco or tomato crops are not available, these weedy nightshades serve as the primary breeding ground.
Not All Nightshades Are Equal
Hornworms do have preferences within the Solanaceae. Research on female hawkmoths (the adult form of hornworms) showed they strongly preferred laying eggs on plants in certain subgroups, especially those in the subgenus Potatoe (which includes tomato and potato), Nicotiana (tobacco), and Datura, compared with peppers (Capsicum), ground cherries (Physalis), and some other Solanum subgenera.2Ecological Entomology. Tritrophic interactions reinforce a negative preference–performance relationship in the tobacco hornworm (Manduca sexta) This preference hierarchy matters for gardeners: if you grow tomatoes and peppers side by side, the hornworms will overwhelmingly favor the tomatoes.
The ranking is not just about what tastes good to the caterpillar. Adult moths choosing where to lay eggs are balancing several factors at once, including leaf chemistry, leaf texture, and even the risk of predators and parasites that patrol certain plants more heavily. The result is that some nightshade species get hammered while others nearby may go largely untouched, even though the larvae could technically survive on either.
Surprising Non-Nightshade Hosts
Despite their reputation as strict nightshade specialists, hornworms can be coaxed onto and even thrive on a handful of plants outside the Solanaceae. In a systematic study testing first-instar tobacco hornworm larvae on ten nightshade and twelve non-nightshade species, researchers found that three non-host species were “acceptable” enough to support growth all the way to the fifth instar. The study proposed dividing plants into three categories for hornworms: true hosts, acceptable non-hosts, and unacceptable non-hosts.3Entomologia Experimentalis et Applicata. Foodplant selection and induction of feeding preference among host and non‐host plants in larvae of the tobacco hornworm Manduca sexta
Earlier work found that when the caterpillars’ mouthpart sensory organs (maxillae) were surgically removed, they would readily eat dandelion (Taraxacum officinale), burdock (Arctium minus), and mullein (Verbascum thapsus), all plants they normally refuse to touch.4Entomologia Experimentalis et Applicata. The Consumption, Digestion and Utilization of Solanaceous and Non-Solanaceous Plants by Larvae of the Tobacco Hornworm, Protoparce sexta (Johan.) (Lepidoptera: Sphingidae) The caterpillars could digest these plants perfectly well; they simply refused them because their taste sensors detected something “wrong.” This tells us that the hornworm’s specialization on nightshades is driven more by what it chooses to eat than by what it can physically digest.
Perhaps the most interesting wild exception occurs in Arizona, where hornworm larvae have been recorded eating devil’s claw (Proboscidea parviflora), a plant in the entirely unrelated family Martyniaceae. Genetic analysis of Manduca sexta populations across the United States found that Arizona hornworms show distinct genetic differences, including what appears to be a loss-of-function change in a larval sensory gene. Researchers have speculated, though not yet confirmed, that the loss of a single taste receptor could be enough to turn a strict specialist into a caterpillar willing to try new things, as similar knockout experiments in silkmoths have demonstrated.5G3 Genes|Genomes|Genetics. Population differentiation and structural variation in the Manduca sexta genome across the United States
How Hornworms Choose What to Eat
A hornworm’s food selection is not a simple yes-or-no decision. It is a multi-step screening process driven by chemical sensors in and around the mouth. The caterpillar has two main checkpoints: the maxillary styloconica (small sensory organs near the mouthparts) and a second set of chemoreceptors lining the roof of the preoral cavity, called epipharyngeal sensilla. Even when researchers removed the antennae and maxillary organs, larvae still managed to tell the difference between a host plant like tomato and a non-host plant like canna lily. The epipharyngeal sensors appear to function as a backup system that detects feeding deterrents, chemicals in non-host leaves that tell the caterpillar to stop eating.6Entomologia Experimentalis et Applicata. Chemoreceptors in the Preoral Cavity of the Tobacco Hornworm, Manduca sexta, and Their Possible Function in Feeding Behaviour
This layered sensory system means that hornworms are not simply attracted to nightshades. They are repelled by almost everything else. Many plants produce bitter or toxic compounds that trigger avoidance in intact hornworms, which is why removing the taste organs opens up a much wider diet. The caterpillar’s gut can handle a broader range of leaves than its brain will permit it to eat.
Surviving the Poison in Their Food
Nightshade plants are famously toxic, loaded with alkaloids like nicotine in tobacco and glycoalkaloids like tomatine in tomatoes. Hornworms have evolved a remarkably straightforward strategy for dealing with nicotine: they excrete it. Research showed that tobacco hornworms absorb nicotine into their blood, but rather than breaking it down into less toxic byproducts, they simply push it back out through excretion and egestion before it accumulates to a dangerous level at its site of action in the nervous system.7Journal of Insect Physiology. Adaptation of tobacco hornworms to the ingestion of nicotine There was no evidence that hornworms chemically detoxify nicotine at all. They just get rid of it fast enough that it never builds up.
This nicotine tolerance is more than just a defense against the plant. It may function as a weapon against parasites. Hornworms ingesting nicotine-rich diets appear to impair the development of parasitoid wasps like Cotesia congregata, which lay their eggs inside the caterpillar. By feeding on high-nicotine tissue, the hornworm essentially poisons its own parasites.8Academia.edu. Self Medication as a Response to Parasitoid Infection in the Tobacco Hornworm, Manduca sexta Whether hornworms deliberately seek out higher-nicotine leaves when parasitized is still an open question, but the protective effect itself is well documented.
Broader research on caterpillar gut bacteria has revealed another layer of defense against plant toxins. In lepidopteran species generally, gut bacteria can break down toxic plant compounds and use them as an energy source, effectively disarming the plant’s chemical defenses from the inside. One study demonstrated this causally: a gut bacterium isolated from silkworms could degrade a specific plant toxin, and when transferred to a caterpillar species that normally could not handle that toxin, it conferred resistance.9PubMed Central. Gut bacteria of lepidopteran herbivores facilitate digestion of plant toxins Whether hornworms rely on similar microbial partnerships for handling specific nightshade toxins beyond nicotine is an active area of investigation.
What the Plants Do in Response
Nightshade plants are not passive victims. Tomatoes, for example, fight back even before a hornworm takes its first bite. Research on tomato plants showed that simply touching or breaking the tiny glandular trichomes (hair-like structures) on the leaf surface, as a caterpillar or moth does while crawling, triggers an immune-like defense response. The plant ramps up production of proteinase inhibitors, proteins that interfere with the caterpillar’s ability to digest its food. This response is triggered by jasmonic acid released from the damaged trichomes and also requires hydrogen peroxide formed on the leaf surface. The plant does not need to be chewed on to start defending itself; physical contact alone is enough to sound the alarm.10PubMed Central. Plants on early alert: glandular trichomes as sensors for insect herbivores
This is part of why the relationship between hornworms and their hosts is a genuine arms race. The caterpillars have evolved rapid excretion of nicotine and a sensory system finely tuned to detect and avoid the most toxic tissues. The plants have evolved contact-triggered defenses, sticky trichomes, and chemical cocktails that make digestion harder. Each side pushes the other to escalate.
Tobacco Hornworm Versus Tomato Hornworm
The two species most commonly encountered in gardens, Manduca sexta (tobacco hornworm) and Manduca quinquemaculata (tomato hornworm), are easy to confuse. Both are large green caterpillars with a prominent horn on the rear end, and both attack the same set of crops. The quickest visual distinction: the tobacco hornworm has seven diagonal white stripes on each side and a red or red-orange horn, while the tomato hornworm has eight V-shaped markings and a typically black or dark blue horn.
Their host-plant ranges overlap almost entirely. Both feed on tomato, tobacco, pepper, eggplant, potato, and wild nightshades. In field surveys, they were frequently found together on the same tomato plants.11Wiley Online Library / Pest Management Science. High tunnels: protection for rather than from insect pests? For practical purposes, the control strategies and host-plant awareness needed are identical for both species, which is why many gardening references simply lump them together as “hornworms.”
What Hornworms Mean for Your Garden
If you grow tomatoes, peppers, or eggplant, hornworms are among the most destructive caterpillars you will encounter. A single large hornworm can defoliate a substantial portion of a tomato plant in a day or two, eating leaves, stems, and even unripe fruit. They are hard to spot despite their size because their green coloring blends remarkably well with tomato foliage.
Knowing their host-plant preferences gives you a practical edge. Because hornworms strongly prefer tomatoes over peppers, you can sometimes use this to your advantage by planting trap crops. Wild nightshades like jimson weed and ground cherry growing near a garden can draw egg-laying moths away from your prized tomatoes, though this cuts both ways: if those weedy nightshades are growing nearby, they may also serve as a nursery for hornworm populations that later migrate to your garden. Clearing wild nightshades from the immediate area around your garden is a sensible first step.
Hand-picking remains the most effective control method for home gardeners. Look for the caterpillars in the early morning or late evening, when they tend to feed more actively on upper foliage. Their frass (droppings), which looks like small dark pellets on lower leaves, is often the first sign you have hornworms before you spot the caterpillars themselves. Bacillus thuringiensis (Bt), a naturally occurring soil bacterium, is widely used as an organic spray and is effective against young hornworm larvae.
One important thing to watch for: if you find a hornworm covered in small white cocoons, leave it alone. Those cocoons belong to parasitoid wasps, usually Cotesia congregata, which have laid their eggs inside the caterpillar. The hornworm is already doomed, and the emerging wasps will go on to parasitize more hornworms. Removing parasitized hornworms actually works against your interests.
Diet Effects on Hornworm Appearance
Gardeners and researchers have long noticed that hornworms raised on different diets look different. In the laboratory, hornworms raised on tomato leaves are bright green, while those raised on artificial diet turn a blue or blue-green color. The green color comes from a combination of a blue bile pigment protein and a yellow carotenoid protein, together forming a complex called insectoverdin. On artificial diet, the caterpillar still produces the blue pigment but lacks the plant-derived yellow carotenoid, so it appears blue.12PLoS One. Standardized methods for rearing a moth larva, Manduca sexta, in a laboratory setting – Section: Larval color is affected by diet
This is mostly relevant to laboratory researchers and breeders who raise hornworms commercially as reptile food, but it does explain something home gardeners occasionally notice: a hornworm that has been feeding on one host plant species can look subtly different from one on another, depending on the carotenoid content of the foliage it has been eating.
Geographic Variation in Host Use
Hornworm populations are not identical across the continent. The Arizona devil’s claw example is the most dramatic illustration, but the principle is broader: hornworm populations in different regions can show distinct feeding behaviors and genetic makeups. Analysis of Manduca sexta genomes from populations across the United States revealed clear population differentiation, with genetic structural variants that differ between geographic groups.5G3 Genes|Genomes|Genetics. Population differentiation and structural variation in the Manduca sexta genome across the United States
This kind of geographic variation in host use has been well studied in other specialist insects too. In the Baltimore checkerspot butterfly, for example, populations in Massachusetts were far more likely to accept a non-traditional host plant (English plantain) than populations from Maryland, and the plant’s geographic origin mattered as well. Massachusetts females accepted Massachusetts-grown plantain about half the time, but Maryland-grown plantain only about a fifth of the time.13PubMed Central. Novel host plant use by a specialist insect depends on geographic variation in both the host and herbivore species The broader lesson is that specialist insects can shift their diets in ways that depend on local adaptation of both the insect and the plant, and hornworms are no exception. What a hornworm in Arizona considers food may not match what a hornworm in Virginia will eat.
Hornworms as Feeder Insects
Beyond their role as garden pests, hornworms have become one of the most popular feeder insects in the reptile and amphibian pet trade. Their large size, soft bodies, and high moisture content make them attractive food for bearded dragons, chameleons, and other insectivorous pets. Commercially raised hornworms are typically fed artificial diets rather than nightshade leaves, partly for convenience and partly because hornworms that have been eating tobacco or tomato foliage can carry plant alkaloids in their tissues. The nicotine-excretion mechanism described earlier means that hornworms clear most nicotine relatively quickly, but commercially raised feeder hornworms avoid the issue entirely by never encountering nightshade chemistry in the first place.
The blue-green coloring of diet-raised hornworms versus the bright green of plant-fed ones is immediately apparent to anyone who has seen both. It is purely cosmetic and has no bearing on nutritional quality, but it does serve as a quick visual indicator of what the caterpillar has been eating.
Wild Hosts That Act as Seasonal Bridges
For farmers growing tobacco or tomatoes commercially, understanding the full host-plant roster matters because wild nightshades serve as seasonal bridges. In the early spring, before crops are planted, hornworm moths emerging from overwintering pupae in the soil lay their eggs on whatever nightshades are available, often jimson weed, horsenettle, or ground cherry. These early-season wild hosts sustain the first generation of caterpillars. When crops are transplanted into fields a few weeks later, the second generation of moths has a much larger and more nutritious target available.1Oxford Academic. Seasonal Parasitism and Predation of Eggs of the Tobacco Hornworm on Various Host Plants in Kentucky
Managing wild nightshades around field edges can reduce the size of that bridge population, but it is a tricky balancing act. Wild nightshades also harbor natural enemies of hornworms, including egg parasitoids and predators that keep hornworm numbers in check. Removing all wild nightshades could paradoxically reduce the natural-enemy population more than the hornworm population, since the parasitoids and predators depend on those early-season hosts to build their own numbers before the crop season begins. Integrated pest management programs for tobacco and tomato typically recommend monitoring wild-host populations rather than eliminating them outright.