Sphinx moth caterpillars are leaf-eating machines that feed on the foliage of specific host plants, while the adults are mostly nectar drinkers that use an extraordinarily long, coiled tongue to sip from deep-throated flowers. The family Sphingidae includes roughly 1,500 species worldwide, and their diets vary more than you might expect. Some adults raid beehives instead of visiting flowers, and a few species barely eat at all once they have wings. The caterpillar side of the story is just as varied, with host plant choices that range from a single plant family to dozens.
What the Caterpillars Eat
Sphinx moth caterpillars, commonly called hornworms because of the small horn or spike on their rear end, feed almost entirely on the leaves of their host plants. Different species within the family target different plants, and the range of acceptable hosts varies by lineage. Research on Southeast Asian sphingid caterpillars found that diet breadth and the diversity of utilized host plants differ between subfamilies and tribes, suggesting that evolutionary history shapes what each species can eat. Some sphinx moth caterpillars are strict specialists, feeding on just one or two plant families. Others are generalists that will munch through a wider botanical menu.
The two most familiar species in North America illustrate this well. The tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquemaculata) both target plants in the nightshade family, including tobacco, tomato, pepper, and eggplant. These caterpillars cause real economic damage to crops. Both species can strip a tomato plant’s foliage down to bare stems in a few days, and the losses to growers can be substantial.1Pedobiologia. Effect of aqueous extracts from vermicomposts on attacks by cucumber beetles (Acalymna vittatum) (Fabr.) on cucumbers and tobacco hornworm (Manduca sexta) (L.) on tomatoes Other sphinx moth species feed on entirely different plants: the white-lined sphinx moth caterpillar eats evening primrose, portulaca, and various wildflowers, while the pandora sphinx moth caterpillar targets grape and Virginia creeper.
The caterpillars’ appetites are impressive by any standard. During the fifth and final larval stage, a tobacco hornworm roughly doubles its body weight every day or two. Research on fifth-instar Manduca sexta larvae found that their approximate digestibility was about 60 percent, meaning they absorbed a little more than half of the dry weight and energy of the food they consumed. That digestibility held steady even as the caterpillar grew dramatically in size and ate more each day.2Journal of Insect Physiology. Food and water economy and its relation to growth in fifth-instar larvae of the tobacco hornworm, Manduca sexta The remaining 40 percent passes through as frass, the polite term for caterpillar droppings, which are conspicuously large pellets gardeners often notice before they spot the well-camouflaged caterpillar.
How Tobacco Hornworms Survive Nicotine
Feeding on tobacco presents an obvious problem: the leaves are loaded with nicotine, one of the more potent plant toxins in nature. Tobacco hornworms have evolved a remarkably effective system for dealing with it. Early research suggested that the caterpillars simply excreted intact nicotine before it could accumulate to a toxic dose.3Journal of Insect Physiology. Adaptation of tobacco hornworms to the ingestion of nicotine Later work revealed the picture is more complex: the caterpillars rapidly metabolize most of the nicotine they ingest, converting it into less harmful breakdown products. The pattern of metabolites changes over time as midgut enzymes ramp up, and the major metabolite has been identified as cotinine-N-oxide.4Insect Biochemistry and Molecular Biology. Metabolic fate of the allelochemical nicotine in the tobacco hornworm Manduca sexta
The speed of this induction is striking. When nicotine-naive caterpillars are injected with nicotine, about a third of the dose is still circulating in the blood 15 minutes later. But in caterpillars that have already been eating nicotine-containing leaves, 97 percent of the dose is cleared or broken down in the same time frame.4Insect Biochemistry and Molecular Biology. Metabolic fate of the allelochemical nicotine in the tobacco hornworm Manduca sexta The detoxification system is also reversible: within 24 hours of switching to a nicotine-free diet, the caterpillar’s ability to break down nicotine drops sharply. More recent molecular work has shown that ingesting nicotine triggers accumulation of specific detoxification gene transcripts in M. sexta larvae, though the exact metabolic products remain a subject of some scientific debate between older and newer studies.5PubMed Central. Differences in nicotine metabolism of two Nicotiana attenuata herbivores render them differentially susceptible to a common native predator
Interestingly, nicotine may not be purely a burden for the caterpillar. Research on Manduca sexta found that dietary nicotine appeared to stimulate the phenoloxidase immune response, an enzyme system involved in fighting pathogens and parasites. Plant toxicity did reduce growth and slow development, as expected, but it did not trade off against immune function. Nicotine, in other words, may function partly as a medicine.6Functional Ecology. Toxin or medication? Immunotherapeutic effects of nicotine on a specialist caterpillar
How Mother Moths Choose the Menu
Caterpillars do not pick their own host plants. The female moth selects where to lay her eggs, and the caterpillar eats whatever it hatches on. Female Manduca sexta use the scent profiles of host plants to make these decisions, and research has shown they are surprisingly discriminating. In wind-tunnel experiments, female moths significantly preferred the scent of Datura wrightii (sacred datura) over Nicotiana attenuata (coyote tobacco), even though both are acceptable host plants. This preference held up even when the concentration of the tobacco plant’s scent was diluted to match the datura’s, suggesting the moths distinguish between the actual chemical composition of the scent blends, not just their strength.7PLOS ONE. Host Plant Odors Represent Immiscible Information Entities – Blend Composition and Concentration Matter in Hawkmoths When the two plant scents were mixed together, any preference disappeared entirely, implying the moths need a clean signal to make a choice.
What Adult Sphinx Moths Drink
Once a sphinx moth emerges from its pupal case with wings, it switches to an entirely liquid diet. The vast majority of species are nectar feeders, hovering in front of flowers like hummingbirds and uncoiling a long, straw-like proboscis to reach deep into tubular blossoms. Proboscis lengths across the sphinx moth family range from just a few millimeters to more than 200 millimeters, depending on species.8PubMed Central. Evolutionary functional morphology of the proboscis and feeding apparatus of hawk moths (Sphingidae: Lepidoptera) That upper range is over eight inches, long enough to reach nectar at the bottom of the deepest tropical orchid spurs.
This proboscis length is central to a famous story in evolutionary biology. Darwin predicted in 1862 that a moth with an extremely long tongue must exist to pollinate the Malagasy star orchid, which has a nectar spur roughly 30 centimeters deep. Decades later, the hawk moth Xanthopan morganii praedicta was confirmed as the pollinator. But long-tongued hawkmoths are not limited to a single highly specialized flower. They also visit less specialized flowers with short tubes, feeding opportunistically when deep-throated blossoms are not available.9ResearchGate. Evolution of Long-Tongued Hawkmoths and Pollination of Long-Spurred Angraecoid Orchids
A global analysis of hawkmoth pollination found that proboscis length is a key factor shaping which flowers a moth species can access. Plants that depend on hawkmoth pollination have evolved floral tube lengths and nectar volumes that match the tongue lengths of their local moth pollinators.10PubMed Central. The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks Some of these flowers have also evolved visual features to attract the moths, including large petals with deeply divided, fringed margins that appear to exploit the moths’ preference for conspicuous shapes.11Flora. Hawk-moth pollination and elaborate petals in Cucurbitaceae: The case of the Caribbean endemic Linnaeosicyos amara
Nectar Is More Than Fuel
Sphinx moths are among the most metabolically demanding fliers in the animal kingdom. Hovering in front of a flower while feeding requires enormous energy, and the nectar they drink is not just calories. Research published in Science found that sugar-fed moths had lower oxidative damage to their flight muscle membranes than unfed moths. The moths shunt nectar glucose into the pentose phosphate pathway, which generates molecules that neutralize the damaging byproducts of intense aerobic exercise.12PubMed. Hawkmoths use nectar sugar to reduce oxidative damage from flight Nectar, in other words, functions partly as an antioxidant, protecting the flight muscles from the very metabolic demands that feeding requires. For a moth that may fly many kilometers in a single night, this is not a minor perk.
Moths are also pickier about nectar quality than you might assume. Manduca sexta strongly prefers higher sucrose concentrations, which makes intuitive sense since more sugar means more energy. But experienced moths also learn to forage for nectar that contains amino acids, the building blocks of protein. In laboratory tests, moths that learned to associate a flower color with amino-acid-enriched nectar shifted their foraging preference toward those flowers, even when the color conflicted with their natural inclinations. The strength of this learned preference was comparable to a 5 percent difference in sugar concentration, which is a meaningful nutritional signal.13PubMed Central. Associative learning of non-sugar nectar components: amino acids modify nectar preference in a hawkmoth
The Death’s Head Hawkmoth and Honey Raiding
Not every adult sphinx moth sips politely from flowers. The three species of death’s head hawkmoth (Acherontia) are honey thieves. They enter beehives and feed directly from the combs, a behavior known as cleptoparasitism. This feeding strategy is unique among hawkmoths.14Systematic Entomology. Phylogeny of the death’s head hawkmoths, Acherontia [Laspeyres], and related genera (Lepidoptera: Sphingidae: Sphinginae: Acherontiini) Field observations have documented Acherontia atropos raiding honeybee colonies in locations ranging from Europe to Pakistan.15Journal of Agriculture and Veterinary Science. First record of Deaths Head Hawkmoth Acherontia atropos (Linnaeus, 1758) (Lepidoptera: Sphingidae), A Kleptoparasite of Honey Bees from Rahim Yar Khan, Punjab, Pakistan
The moths have evolved physical adaptations for this lifestyle. Their proboscis is short and stout compared to nectar-feeding relatives, better suited for piercing wax comb cells and sucking up viscous honey. Researchers have hypothesized that feeding on thick honey drove the evolution of a specialized valve structure at the opening of the pharynx, a modified epipharynx that allows efficient intake. This same valve may have been co-opted for another of the death’s head hawkmoth’s famous traits: the ability to produce a loud squeaking sound, thought to mimic honeybee acoustics and reduce aggression from hive defenders.16PubMed. The unique sound production of the Death’s-head hawkmoth (Acherontia atropos (Linnaeus, 1758)) revisited
Sphinx Moths That Barely Eat as Adults
At the opposite extreme from death’s head hawkmoths, a few sphinx moth species have adults that eat little or nothing. These species rely entirely on the fat reserves they accumulated as caterpillars, and their adult stage is focused almost exclusively on reproduction. Morphological studies have found that even supposedly nonfeeding species still possess a proboscis and internal suction pump with the same basic architecture as their nectar-feeding relatives, just scaled down to a few millimeters.8PubMed Central. Evolutionary functional morphology of the proboscis and feeding apparatus of hawk moths (Sphingidae: Lepidoptera) Whether these vestigial mouthparts allow occasional opportunistic feeding or are truly non-functional remains an open question. It does suggest that the transition from feeding to non-feeding adult life has happened relatively recently in these lineages, evolutionarily speaking.
How They Find Flowers in the Dark
Most sphinx moths feed at dusk or at night, which raises the question of how they locate the right flowers. The answer involves both smell and surprisingly good color vision. Hawkmoths have three types of color receptors sensitive to ultraviolet, blue, and green light. Nocturnal species including Deilephila elpenor and Hyles lineata can discriminate flower colors at light levels equivalent to starlight, intensities at which humans and honeybees are effectively color-blind.17Oxford Academic. Colour Vision in Diurnal and Nocturnal Hawkmoths They also learn and remember flower colors, pairing visual cues with scent to build a mental map of which flowers are rewarding. This combination of acute low-light vision and associative learning makes sphinx moths some of the most effective nocturnal pollinators on the planet.
When Parasites Hijack a Caterpillar’s Appetite
The feeding life of a sphinx moth caterpillar does not always go according to plan. One of the most dramatic disruptions comes from the parasitoid wasp Cotesia congregata, which lays its eggs inside living hornworm caterpillars. The wasp larvae develop internally, feeding on the caterpillar’s tissues, and eventually bore through the skin to pupate in small white cocoons on the host’s back. The effect on the caterpillar’s feeding is severe and progressive. Parasitized caterpillars consume less leaf area, have shorter feeding bouts, and take longer pauses between meals compared to healthy caterpillars.18Journal of Experimental Biology. Manduca sexta caterpillars parasitized by the wasp Cotesia congregata stop chewing despite an intact motor system
What makes this especially interesting is that the caterpillar’s jaw muscles still work. The feeding suppression is not caused by physical damage to the chewing apparatus but by chemical manipulation from the wasp larvae. Research has shown that secretions from late-stage wasp larvae reduce the host’s weight gain when injected into healthy caterpillars, suggesting the wasps release substances that directly suppress feeding behavior.19Journal of Experimental Biology. The parasitic wasp Cotesia congregata uses multiple mechanisms to control host (Manduca sexta) behaviour In the final day before the wasp larvae emerge, the caterpillar stops eating entirely, ceases all spontaneous movement, and its metabolism drops dramatically.20Journal of Insect Physiology. Effects of Parasitism by the Braconid Wasp Cotesia congregata on Metabolic Rate in Host Larvae of the Tobacco Hornworm, Manduca sexta At that point the caterpillar is essentially a zombie bodyguard, sometimes remaining alive for days while sitting motionless over the wasp cocoons and protecting them from predators.
What Happens When Caterpillars Get the Wrong Diet
Laboratory studies that manipulate caterpillar diets have revealed how sensitive sphinx moth larvae are to nutritional balance. When Manduca sexta caterpillars were reared on diets with high fat content, the results were stark. Young larvae on high-fat diets suffered about 80 percent mortality and had body masses roughly 43 percent lower than those on medium- or low-fat diets. Even caterpillars that did not start the high-fat diet until their fourth instar still grew significantly more slowly than controls. By day four of the fifth instar, high-fat-fed caterpillars had daily growth rates six times lower than caterpillars on low-fat diets.21PubMed Central. Effects of high-fat diet on feeding and performance in the tobacco hornworm, Manduca sexta These findings underscore that sphinx moth caterpillars are finely tuned to a leaf-based diet rich in protein and carbohydrates but low in fat. The natural foliage they consume meets this profile well, but any substantial shift away from it has outsized consequences.
Sphinx Moths as Pollinators and Pests
The feeding habits of sphinx moths put them at the center of two very different human concerns. On the agricultural side, hornworm caterpillars are among the most damaging pests of tomato and tobacco crops. Greenhouse and field trials have explored biological control strategies, including vermicompost-amended soil, which has been shown to reduce the foliage damage caterpillars inflict.22Pedobiologia. Suppression of tomato hornworm (Manduca quinquemaculata) and cucumber beetles (Acalymma vittatum and Diabotrica undecimpunctata) populations and damage by vermicomposts Gardeners who grow tomatoes in temperate regions are likely to encounter hornworms at some point, and hand-picking remains a common first-line defense in home gardens.
On the ecological side, adult sphinx moths are critically important pollinators, especially for night-blooming flowers that have coevolved to depend on them. Because hawkmoths cover large distances during nightly foraging flights, they maintain gene flow across plant populations separated by distances that shorter-range pollinators cannot bridge.23PubMed. Hawkmoth and bee pollinators impact pollen dispersal at the landscape but not local scales in two species of Oenothera In tropical ecosystems, entire guilds of orchids, night-blooming cacti, and other deep-flowered plants depend on sphinx moths for reproduction. Losing these moths would leave those plants without a pollinator that can reach their nectar, a relationship that in many cases has been refined over millions of years of reciprocal evolution.