Sphinx moth caterpillars, also known as hornworms, are the larvae of sphinx moths (family Sphingidae). There are many different species of sphinx moths, and some of their caterpillars can potentially cause damage to agricultural crops or gardens. However, most sphinx moth caterpillars do not cause serious harm, and some are even beneficial insects. Here is a look at whether sphinx moth caterpillars are truly harmful or not.
What are sphinx moths and their caterpillars?
Sphinx moths, also called hawk moths, are a family of large, heavy-bodied moths with long, narrow forewings and a wingspan ranging from 1 to over 10 inches. They are characterized by their swift, sustained flying abilities resembling that of a hummingbird, and their caterpillars are called hornworms due to the horn-like structure on their hind end.
There are over 1,400 species of sphinx moths worldwide, with around 30 species native to North America. Some of the most common North American species include the tomato hornworm, tobacco hornworm, Carolina sphinx, laurel sphinx, grapevine sphinx, pandorus sphinx, and more. The caterpillars of different sphinx species feed on various host plants – tomatoes, tobacco, grapes, smartweeds, apple, elm, and more.
Life cycle
Sphinx moths have a complete metamorphosis life cycle. The adult female lays eggs on the leaves of host plants. The eggs hatch into larvae or caterpillars, which feed voraciously on the leaves. The caterpillar goes through 5-6 instars over 2-3 weeks, reaching a length of 3-4 inches when fully grown. It then forms a pupa and undergoes metamorphosis over 1-2 weeks. Finally, the adult moth emerges to start the cycle again.
Appearance
Sphinx moth caterpillars are quite large, ranging from 2-4 inches long when fully grown. They have a cylindrical body shape. Their most distinctive feature is the horn at the rear end, giving them the name hornworms. They usually have diagonal stripes or other markings along the body. The pupa is enclosed in a cocoon underground.
Adult sphinx moths have narrow forewings and more broad hindwings, allowing for their fast flight. They have stout, hairy bodies and long proboscises to drink nectar from flowers. Their antennae are often thickened or hooked at the tip. Many sphinx moths are quite large with a wingspan over 5 inches, though some are smaller.
Potential for crop damage
The voracious appetite of sphinx moth caterpillars, combined with their large size, means they can sometimes cause significant defoliation to crops and plants if infestations are dense. However, most sphinx moths are not major agricultural pests. Only a handful of species cause occasional economically important levels of crop damage.
Tomato hornworm
The tomato hornworm (Manduca quinquemaculata) and closely related tobacco hornworm (Manduca sexta) feed on plants in the Solanaceae family, which includes tomato, tobacco, eggplant, and potato. They can strip these plants of their leaves very quickly when present in large numbers.
Grapevine sphinx
Grapevine sphinx caterpillars (Sphinx vashti) feed on grapes and Virginia creeper. Heavy infestations may significantly defoliate vines.
Elm sphinx
The larvae of the elm sphinx or four-horned sphinx (Ceratomia amyntor) feed on elm, basswood, and other trees, sometimes causing complete defoliation on young saplings if abundant.
Catalpa sphinx
Catalpa sphinx moth caterpillars (Ceratomia catalpae) can occasionally skeletonize catalpa leaves when at high density.
Benefits of sphinx moths
While a small number of sphinx moth caterpillars can damage crops at high density, the majority of species are harmless or even provide ecosystem services.
Pollination
Adult sphinx moths are important pollinators of many night-blooming flowers, including orchids, petunias, jasmine, and more. Their long proboscises allow them to reach nectar in deep, tubular flowers. By transferring pollen between blossoms, they pollinate these plants.
Prey for other species
Sphinx moth caterpillars provide a food source for many birds, small mammals, and other insect predators, supporting wildlife diversity.
Insect pest control
Some sphinx moth caterpillars are specialists that feed on weeds and other undesirable plant species, helping control their growth. For example, the wild potato sphinx consumes buffalobur nightshade, a problematic agricultural weed.
Are sphinx moths caterpillars dangerous to humans?
Sphinx moth caterpillars are not dangerous to humans. They do not sting, bite, or transmit any diseases. There are a few aspects to be aware of, however:
Spines and irritating hairs
Some sphinx moth caterpillars have small spines or irritating hairs that may cause skin irritation through contact, especially in sensitive individuals. The tomato hornworm is an example. However, serious reactions are very rare.
Allergies
Rarely, individuals with severe allergy to caterpillars may react with hives, asthma, or anaphylaxis from touching sphinx moth larvae. But such severe allergies are very uncommon.
Plant toxins
A few sphinx moth caterpillars feed on plants containing toxic compounds, which are retained in their bodies for defense. For example, oleander hawk moth caterpillars eat oleanders, which contain cardiac glycosides. Accidentally ingesting the caterpillar could potentially be dangerous, though this is very unlikely to occur.
Keeping sphinx moth caterpillar populations under control
For sphinx moth species that occasionally cause significant crop damage like tomato hornworms, various control measures can keep their populations limited to prevent economic loss. Here are a few options:
Manual removal
Manually picking caterpillars off infested plants and dropping them into soapy water or a container with vegetable oil can provide effective control in small gardens. Check plants regularly for any larvae or egg clusters.
Natural predators
Encouraging natural enemies like parasitic wasps, predatory stink bugs, and birds can reduce caterpillar populations. Avoid use of broad-spectrum insecticides which may kill beneficial predators.
Targeted insecticides
When infestations are severe, using microbial insecticides based on Bacillus thuringiensis (Bt) is an option. Spinosad and tebufenozide are caterpillar-specific insecticides that can also be used.
Protective row covers
Row covers over crops can physically exclude moths from laying eggs. Ensure covers do not create overheating issues though.
Crop rotation
Rotating tomato family crops to different parts of the garden each year helps break sphinx moth life cycles.
Sanitation
Removing and destroying crop debris after harvest eliminates potential overwintering sites for pupae.
Conclusion
Most sphinx moth caterpillars are not truly harmful insects. Their damage to agriculture is occasional and limited to just a few species. Many sphinx moths are important pollinators as adults, while their larvae provide prey for other wildlife. Simple control measures can protect against the small number of sphinx moth pests without disrupting the benefits from the majority of harmless or beneficial species.
Sphinx moth caterpillars – summary table
| Species | Food plants | Level of crop damage | Benefits |
|---|---|---|---|
| Tomato hornworm | Tomato, tobacco, potato | Moderate | Prey for predators |
| Tobacco hornworm | Tobacco, tomato | Moderate | Pollination |
| Carolina sphinx | Ash, lilac, privet | Minor | Weed control |
| Elm sphinx | Elm, basswood, cherry | Minor | Pollination |
| Wild potato sphinx | Buffalobur, nightshade | None | Weed control |
As seen in the summary table, most sphinx moth caterpillars cause little or no crop damage, while providing ecosystem services like pollination and weed control. Only a couple species such as tomato hornworms occasionally reach pest status, but can be controlled through various organic methods if needed.
