Hornworm: All You Need to Know About This Garden Pest

Hornworms are fascinating caterpillars that can be found in gardens, feeding on the leaves and fruits of various plants. These large, camouflaged creatures often go unnoticed until significant damage has been done to your plants. Some common species include tomato hornworms (Manduca quinquemaculata) and tobacco hornworms (Manduca sexta), which share similarities in appearance, life cycle, and host plant preferences. They can grow up to three inches in length, making them one of the largest types of caterpillars found in some regions.

These stealthy creatures are not only interesting in their larval stage but also transform into large, fast-moving hawkmoths with a wingspan of up to five inches. Adult hornworms are often mistaken for hummingbirds due to their size, rapid wingbeats, and quick movements. While hornworms can cause extensive damage in gardens, understanding their lifecycle and habits can help with effective management to protect your plants.

Understanding Hornworms

Hornworm Caterpillars

Hornworm caterpillars are the larval stage of the hawk moth, belonging to the family Sphingidae. They have a distinct green color and can grow up to four inches in length. Some common types include the tobacco hornworm and the tomato hornworm. These caterpillars primarily feed on plants from the Solanaceae family, which include tomatoes, peppers, eggplants, and tobacco.

Characteristics:

• Green in color
• Up to four inches in length
• Distinct horns protruding from the rear

Adult Moths

The adult stage of hornworms is the hawk moth. These heavy-bodied moths have a wingspan of up to five inches. They are known for their rapid wingbeats and quick movements, often being mistaken for hummingbirds. Adult moths do not cause damage to plants like their larval counterparts.

Features:

• Wingspan up to five inches
• Rapid wingbeats
• Mistaken for hummingbirds

Life Cycle

Hornworms have a typical life cycle consisting of multiple stages: egg, larva, pupa, and adult. The female moth lays eggs on the leaves of host plants. Once the eggs hatch, the green colored larvae emerge and consume the plant’s leaves and stems.

After some time, the larva finds a suitable place to pupate, forming a pupa. When the adult moth emerges, it seeks a mate to continue the life cycle.

Types of Hornworms

Tomato Hornworm

The Tomato Hornworm (Manduca quinquemaculata) is a common pest in gardens, mainly affecting tomato plants. Key features include:

• Green body with white stripes
• Blackdots along stripe edges
• Eight V-shaped markings
• Horn on the rear end

For instance, the Tomato Hornworm caterpillars usually feed on the upper parts of tomato plants, causing damage to leaves and fruit.

Tobacco Hornworm

Tobacco Hornworm (Manduca sexta) is another species affecting plants like tobacco and tomatoes. Some characteristics of this species include:

• Green body with diagonal white stripes
• Reddish-brown horn on the rear end

Tobacco Hornworms show similar behavior as Tomato Hornworms, causing damage to tobacco and tomato plants.

Comparison Table

Diet and Host Plants

Common Host Plants

Hornworms primarily feed on plants from the Solanaceae (nightshade) family, which includes several common garden crops. Some examples of their preferred host plants are:

• Tomato
• Eggplant
• Pepper
• Potato
• Tobacco

These caterpillars tend to start their feeding in the upper parts of plants, where they blend in with leaves and can often go unnoticed until most of the damage is done¹.

Other Plant Varieties

In addition to the common host plants, hornworms can also feed on some species of Solanum weeds and flowering plants². This diverse group of plants can attract adult hornworm moths for nectar feeding. Some other solanaceous plants they might target include:

• Nightshade
• Petunia
• Nicotiana (flowering tobacco)

In summary, hornworms primarily feed on garden crops from the nightshade or solanaceous plant families. They can cause significant damage to plants like tomatoes, eggplants, peppers, potatoes, and tobacco, and may also target weeds and flowering plants in the same family.

Damage and Impact on Gardens

Impact on Vegetable Crops

• Hornworm caterpillars can cause significant damage to vegetable plants, especially tomatoes.
• They feed on leaves, leading to defoliation and negatively affecting fruit production.

For instance, the tomato hornworm and tobacco hornworm primarily target plants in the Solanaceae family, such as tomatoes, peppers, and eggplants. These caterpillars can eat through several leaves and fruit, leading to noticeable damage in home gardens.

Environmental Factors

• Hornworms are more active during summer months.
• Their green color helps them blend into the environment.

During the summer, gardeners may find it challenging to spot these pests due to their camouflaged colors. However, caterpillar droppings can be a telltale sign of their presence. Checking the undersides of leaves is also essential to detect these pests early.

By keeping an eye out for hornworms and taking timely measures, such as handpicking or using biological controls like Bacillus thuringiensis (Bt), gardeners can protect their plants from these voracious eaters.

Controlling Hornworm Infestations

Natural Predators and Beneficial Insects

• Birds: Various bird species feed on hornworms, helping to control infestations.
• Reptiles: Lizards and frogs can eat hornworms and contribute to their control.
• Insects: Beneficial insects such as ladybugs, lacewings, and green lacewings can also help keep hornworm populations in check.

Insecticides and Pesticides

• Chemical insecticides: These can be effective, but may also harm beneficial insects and the environment. Use with caution.
• Organic pesticides: Products like Bt (Bacillus thuringiensis) are safe to use and target hornworms specifically ¹.

Cultural and Mechanical Controls

• Horsenettle: A natural deterrent, planting horsenettle around your garden can help keep hornworms away.
• Hand removal: Check plants regularly and remove hornworms by hand to prevent damage.
• Plant selection: Hawkmoths, the adult stage of hornworms, are less attracted to certain types of tomatoes, helping to reduce infestations.

Common Questions and Considerations

Hornworms as Feeder Insects

Hornworms are large caterpillars that can serve as a nutritious feeder insect for various pets, such as reptiles and amphibians. Some benefits of hornworms as feeders are:

• High moisture content
• Low fat
• Good source of calcium
• Easy to digest

However, some drawbacks to consider are:

• Rapid growth
• Can be expensive

Toxicity and Risks to Pets and Humans

Hornworms are generally harmless to pets and humans. They lack venom and cannot bite or sting. However, it is important to consider potential risks associated with their consumption:

• Diseases from wild hornworms
• Pesticides or chemicals on plants they eat

Care should be taken to source them from trusted suppliers.

Regional Differences and Diseases

Hornworms can be found throughout North America, with some regional variations. The Tobacco Hornworm and Tomato Hornworm are two common species. They can infest gardens and crops and should not be released in the wild.

In the table below, some key differences between these two species are outlined:

Some diseases hornworms might carry include:

• Bacterial and fungal infections
• Parasites, like the Braconid Wasp

It is crucial to obtain hornworms from reputable suppliers and keep them in a clean environment to reduce the risk of diseases.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – What's That Eyecatcher?

I guess you already know that you must have a male cricket to get singing. I have known people who bought large quantities of crickets from the pet store to use in art installations as a sound component, so I know that pet store crickets will sing, though their songs are frail. Additionally, store crickets, usually European House Crickets (Acheta domesticus) are not very attractive, since they are an anemic shade of tan. Garden crickets or Field Crickets (Gryllus species) are a beautiful glossy black and have a robust chirp. Singing generally occurs in spring and early summer. I had a Field Cricket move into my bathroom sink drain many years ago, and it managed to hide somewhere in the pipes whenever I ran the water, though I was careful to not scald the free-loader. My cricket would sing constantly. I would recommend locating a cricket in your garden by tracking its chirp. Give it a cool, dark place and hope for the best. I cannot come up with a logical reason why your captives are mute, and I would suggest patience. Give the guy a chance to adapt, and eventually his romantic inclinations should bring on the song.

March 14, 2002
This is Ken Blanchard from the forum of cryptozoology.com. After inquiring about a weird caterpillar sighting I had years ago, I was referred to your Daniel Marlos. I can’t find a specific e-mail address to him on any of the insect pages, so I’d appreciate it if you would forward this to him.
Seven summers ago, my family and I were camping in the Catskills of New York State. While walking across a sickly campground lawn, I spotted a mostly to entirely pink hornworm crawling across the grass. It was about 5 inches long and about 0.75 inches thick. Its body was very smooth and it lacked the characteristic spine on its rump that is characteristic of hornworms. The lack of a spine appeared to be normal as the larva was
completely uninjured. I captured it and it cocooned itself within a few hours. Being just a foolish kid at the time and not thinking about the possible cryptozoological importance of my find, I threw the cocoon into the woods and never retrieved it. Is there a known lepidopteran in NY that starts out as such a larva? If not, then I made a big mistake, but at least it shows that I can make another entomological discovery here in NY if I try hard enough.

Dear Ken,
Hornworms, the larvae of the sphinx moths, do not form cocoons, choosing instead to bury themselves in the ground where they pupate. Caterpillars from the Saturnidae or giant silk moths, do however, form cocoons. They are also among the largest caterpillars in North America. Members of this family include the Cecropia, the Polyphemus and the Prometheus moths. All have caterpillars of varying shades of green. The adult moths from this family live only a few days, do not eat as adults, and their sole purpose in life is to mate and produce a new generation. One of the rarest and most beautiful of the Saturnidae is the pale green Luna moth which flies near dawn in the late spring.
Your caterpillar was pink. You will not find this caterpillar in any text on North American lepidoptera, which makes it an excellent candidate for cryptozoology. I was lucky enough many years ago, just before dawn on a blue moon in May, to encounter the comely specimen in this photo in Northeastern Ohio. It is a very rare color variation of the luna moth (I am the only known observer) which I have named Actias luna var. magenta. Magenta is the complimentary color to green, the normal hue of the moth, but magenta does not exist in the visible spectrum. It is created when the longest light rays, the red ones, are combined with the shortest light rays, the blue ones, turning the visible spectrum into a man-made color wheel. Magenta has no true wavelength, and since it is composed of the longest and
shortest light rays combined, the color tends to vibrate.
Ken, had you not, in a youthful lapse in judgement, pitched your cocoon into the woods, you might have been fortunate enough to witness a similar moth metamorphose before your very eyes. Tough luck.
Dear What’s that Bug,
Being from Georgia I am used to hearing insects chirping at night and even bullfrogs doing their thing in the backyard. I am fond of these sounds and find them relaxing. And I know that having a cricket inside is supposed to be good luck. (Or is it just good luck if it is in your closet?)
However, the cricket or other chirping insect that is currently residing in my bathroom is not making me happy or relaxed. In fact, it is getting on my nerves and disturbing my sleep. I want to know what I should do. I don’t want to hear this sound that sort of echoes around in my empty bathroom but I don’t really want to kill this bug, nor would I really know how.
I have not spotted the bug, but it is really making it’s presence known. Any advice?
Thanks!
Amanda

Dear Amanda,
There are many folk beliefs in existence about crickets. Their presence in the home is generally thought to be an omen of good fortune in many parts of the world, and in China they are kept in captivity. The Chinese also match crickets for combat in a sport that is as popular there as cock fighting is in other countries. Extravagant wages are made on the outcome of championship fights.
The most common species in Southern California is the Tree Cricket (Oecanthus sp.) which is generally found in gardens and is almost always heard and not seen. They are usually green or white in color and only about 1/2 an inch long. It is common knowledge that the chirp rate of this cricket varies with the surrounding temperature, increasing at higher degrees and decreasing at lower ones. This fact has inspired formulas for calculating the temperature from the number of chirps per minute. The Snowy Tree Cricket, also called the Thermometer Cricket (Oecanthus fultoni) indicates the temperature in degrees Fahrenheit if one counts the number of chirps in 13 seconds and adds 40.
Your tenant is, however, more likely another type of cricket. Field Crickets (Gryllus sp.) are much larger than tree crickets, with body lengths up to 1 1/4 inches. Field Crickets live on the ground in fissures and under litter, vegetation and stones. They sometimes sing in the morning or late afternoon, but more usually at night when they come out to feed on all sorts of organic matter. They occasionally enter homes and become a nuisance by their unwelcome presence and incessant chirping.
A third possibility is that you are hosting a European House Cricket (Acheta domesticus) which are about 3/4 inch long as straw-brown in color. The species was apparently introduced into the eastern United States from Europe, although its original home may have been Africa. It has since become widespread in Southern California, where it is usually associated with human habitations. Lacking a dormancy period and hence being easy to raise, it is sold as fish bait and animal food in pet stores. Its chirp is frail and attracts less attention than that of its Field Cricket relatives. Bathrooms and kitchens are the most likely places to find crickets in the home.
I once had one who lived in the drain of my bathroom sink and I found its chirping to be quite soothing. I think you should lighten up and surrender to the sounds of nature.

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Dear What’s Th
at Bug,
I was walking through the woods yesterday evening when I ran across several of these creatures. We live in the southeastern U.S….these were found near dusk in a drizzle in a forest. I have always heard of them being called ‘cherry bugs’ due to the scent that they emit when startled or feel threatened…they are between 1.5 and 2.5 inches in length, black, with yellow spots down not only the sides, but also down the center of the back as well. All markings are symmetrical. They look *very* similar to a picture I saw of a yellow-spotted millipede…the difference being the extra row of yellow spots down the center of the back….plus, the yellow-spots are from Oregon…and we are in Tennessee. I am curious to know what exactly these are, they are interesting creatures, and I’d like to know a bit more about them. Also, any care advice would be appreciated as well.
Thank you! –
Christina Loder

Dear Christina,
Unfortunately, if you enclosed a photograph, it did not arrive. Based on your description, and your latitude and longitude, I would guess that you have stumbled upon some caterpillars, more specifically, the larvae of some local swallowtail (Papilio sp.) My guess would be the larvae of the black swallowtail butterfly, which feeds on parsley and related plants including Queen Anne’s Lace which grows in uncultivated meadows. The caterpillars are green, black and yellow, and have two orange horns which are hidden near the head. When the caterpillar is threatened, the horns emerge, along with a musty smell that I would not really liken to the scent of cherries. Try this: http://www.ivyhall.district96.k12.il.us/4th/kkhp/
1insects/BSC.html
If you keep them in captivity, you can feed them carrot tops. They will form a crysalid and a butterfly will eventually emerge.

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Dear Readers,

Dear Bugged by Buzzing Behemoth,
To the best of my knowledge, you have had an encounter with a female Valley Carpenter Bee (Xylocopa varipuncta). These very large (1 inch) bees are so named because they bore into wood, forming tunnel-like nests for the rearing of young. Telephone poles and fences are often attacked. The Valley Carpenter Bee has earned itself a bad reputation because of its formidable size and habit of “buzzing” people. The green-eyed male is light brown with golden hairs and looks velvety. The female is a shiny black with bronze reflections on the wings. The female bees can sting, but do so very reluctantly, causing only mild pain.

WHERE ARE THEY NOW?
Late in the afternoon on Labor Day, while preparing for Diorama Club, I noticed a very large, very shiny female Valley Carpenter Bee buzzing loudly and crawling around on a dead branch of my carob tree. I also noticed a perfectly round hole in her proximity. Issuing from the hole was additional buzzing. In the spring, a female VCB had been seen in the vicinity. At that time the honeysuckle was in full bloom along the street, and female VCB’s were often found lapping up nectar. Could it be that I was witnessing the emergence of her brood from the tunnel she had dug for them? I hoped if I watched long enough, I would get to see one of the males. The sexual dimorphism that occurs in the VCB is quite extreme, and a Casual Observer