The Model Organism

Kelly’s Field Notes

Common Name: Hornworms and Sphinx or Hawk Moths

Order: Lepidoptera

Family: Sphingidae

Genera: There are around 200 genera of Sphinx moths

Species of Note Near You (there are around 1,450 species of Sphinx moths):

• Five-spotted hawk moth/Tomato hornworm (Manduca quinquemaculata) - found throughout Australia and the United States, with more in the north than south.

• Blackburn's sphinx moth/Hawaiian tomato horn worm (Manduca blackburni) - it is endemic (only found in) Hawaii, specifically the Big Island, Maui, and Kaho’olawe.

• Caroline sphinx moth/Tobacco hornworm (Manduca sexta) - found throughout the United States, with more in the south than north.

• Hummingbird hawk moth (Macroglossum stellatarum) - found throughout Europe and Asia.

• Death's-head hawkmoth (Acherontia atropos, Acherontia styx and Acherontia lachesis) - found throughout Europe and Africa. Check out our episode, “The Goth Moth,” all about these species.

• fan-tailed bark moth (Callionima nomius) - found throughout Mexico and Central America.

• Cramer's sphinx (Erinnyis crameri) - found throughout South and Central America, and north into the southern United States.

• Oleander hawk moth (Daphnis Nerii) - found in many parts of Asia, Africa, and Hawaii.

Description: 

Adults vary in color but are generally camouflaged to fit in with their surroundings, with browns, tans, black, and white present. Others can be bright, such as the green Oleander hawk moth. Some even mimic bees, with fuzzy plump bodies and banded abdomens. The narrow-banded bee hawk moth (Hemaris tityus) is a great example of this. Generally speaking, the moths that resemble bees or hummingbirds are often seen during the day while those resembling more traditional moths are active in the evenings. Unusual among moths, even males generally do not have very fuzzy antennae. They also do not have tympanic membranes to pick up vibration, but some have hearing organs on their heads (group Choerocampini).

Some adults of these species have very long proboscis! In fact, Charles Darwin was sent an orchid from Madagascar in 1862. The incredibly long nectar tube, 30 cm, was so baffling Darwin exclaimed 'Good heavens, what insect can suck it!' He hypothesized it must be a moth. Alfred Russell Wallce, in 1867, went one step further and assumed it was a hawk moth, based on what he had seen of their longer proboscises across Africa. That moth was later identified and named after Wallace, Wallace's sphinx moth (Xanthopan praedicta); it had a 28.5 cm (11.2 in) proboscis, the longest of all insects.

Hawk moth caterpillars are chunky! Many are around 10.2 cm to 12.7 cm (4 to 5 in) in length, but the largest is the giant sphinx moth (Cocytius antaeus) growing up to 15.2 cm (6 in) in length. They are often referred to as “hornworms” because they have fleshy horns at the end of their bodies. Most are green or brown in color with lighter undersides (countershading). Hornworms are hairless, thick, and sometimes have striping or eye patterns along the sides of their bodies. Eye patterns can be confusing to predators. Some species such as, Hemeroplanes triptolemus, have large eye spots at their rear making them resemble snake heads in appearance. They can even puff it out which makes the “head” more realistic. The adults are called Sphinx moths because at rest, the caterpillar raises its legs off of the surface it is on and tucks its head down, which resembles the Great Sphinx of Giza. 

Life Cycle: 

Female hawk moths lay green eggs on a host plant, usually singly. They can produce several generations a year (multivoltine). Depending on species and environment, eggs hatch within 3 days to twenty-one days. Once they hatch they are eating machines! But, each species is not a generalist and tends to prefer very specific plants. It takes about 24 or so days to go from a little 0.03 gram larva to a chunky 10 gram larva. They then pupate over winter and emerge as adults in the spring. 

Adults are nectar feeders, though there are some weird exceptions. We covered the honey thief, Death's head hawk moth, in another episode. Some species also go for eye secretions (lachryphagy), usually of animals unable to swat them away such as reptiles or sleeping birds. The nectar feeders seem to be more attracted to white flowers than other colors and often those with long flower tubes (see the section above about proboscis length). Orchids are commonly on the menu, where some orchids are exclusively pollinated by hawk moths.

Model Organisms:

The tobacco hornworm (Manduca sexta) is what scientists refer to as a “model organism.” Model organisms are heavily studied species which help scientists understand behavior, physiology, and other biological processes both in those species and extrapolated (expanded) out to others. The tobacco hornworm has been used in studies which help us understand how endogenous hormones and environmental cues affect the development of larvae. Endogenous hormones specifically affect tissue morphology (form) and cell physiology. Other common model organisms are fruit flies (Drosophila melanogaster), mice (usually the house mouse Mus musculus), and roundworms (usually Caenorhabditis elegans). They have also been extensively studied due to their relationship as hosts of the parasitoid wasps in the genus Trichogramma. The tobacco hornworm is easy to rear and study how the parasitoid affects development of the host. Tomato hornworms (M. quinquemaculata) are often also used in these studies. Memorial Sloan Kettering Cancer Center has even been working on replacing many mouse trials with hornworm trials to test drugs before approval for human trials. Other scientists have similarly used hornworms in IBS research.

Super Powers:

• Caterpillar Size - hornworm caterpillars are big hefty stock! They are some of the larger caterpillar species. They are generally around 10.2 cm to 12.7 cm (4 to 5 in) in length, but the largest is the giant sphinx moth (Cocytius antaeus) growing up to 15.2 cm (6 in) in length.

• Toxin Resistance -  tobacco hornworm caterpillars can ingest tobacco and excrete out nicotine rapidly, keeping the caterpillar safe from the nicotine which can be harmful if retained. Other species sequester (store) toxins to use as predator deterrents. 

• Flight - moths fly, it’s what they do! These are also some of the fastest insect fliers, reaching speeds of 19 km/h (11 mph). 

• Hovering - a special ability of some hawk moths, they can hover in place like a hummingbird!

• Side-Slip - hovering hawk moths have the ability to quickly flit from side to side in order to avoid ambush predators in the flowers they drink nectar from.

• Day Walkers - some species of hawk moth are around during the day, often confused for hummingbirds!

• Long Tongues - hawk moths have evolved very long proboscises to reach nectar in long flowers. Wallace's sphinx moth (Xanthopan praedicta) the longest tongue (proboscis) of any insect at 28.5 cm (11.2 in). That’s four times the length of the moth’s body!

• Butt Horn - hornworm caterpillars (but not all Sphingidae caterpillars) have a soft horn on the end of their bodies. What is it for? There are many theories and no definitive answers. Bluff against predators, camouflage, pheromone distributor, sensory organ? There are plenty of theories.

Hornworms in Culture:

• Tomato and tobacco hornworms are common garden pests, eating tomatoes, peppers, and other fruits and vegetables.

• Tomato hornworms are common in the pet trade, used as food for reptiles.

References:

Askham, Beth. “Moth Predicted to Exist by Darwin and Wallace Becomes a New Species.” Natural History Museum, UK, 30 Sept. 2021, www.nhm.ac.uk/discover/news/2021/september/moth-predicted-to-exist-by-darwin-and-wallace-becomes-a-new-species.html.

Byron, Morgan, and Jennifer Gillett-Kaufman. “Tobacco Hornworm, Manduca sexta (Linnaeus); Tomato Hornworm, Manduca quinquemaculata (Haworth).” Entnemdept.ufl.edu, Oct. 2017, entnemdept.ufl.edu/creatures/field/tobacco_hornworm.htm.

Cherif, Asma, Ramzi Mansour, and Kaouthar Grissa-Lebdi. "The egg parasitoids Trichogramma: from laboratory mass rearing to biological control of lepidopteran pests." Biocontrol Science and Technology 31.7 (2021): 661-693.

Cranshaw, W.S. “Hornworms and “Hummingbird” Moths.” Colorado State University Extension, Colorado State University, July 2014, extension.colostate.edu/topic-areas/insects/hornworms-and-hummingbird-moths-5-517/.

Guinness World Records. World’s Longest Insect Tongue. Guinnessworldrecords.com, 2024, www.guinnessworldrecords.com/world-records/112734-longest-insect-tongue. Accessed 12 July 2024.

“Move Over, Mice: Caterpillars Could Replace Some Mammals in the Study of Human Disease.” Memorial Sloan Kettering Cancer Center, 12 Jan. 2023, www.mskcc.org/news/move-over-mice-caterpillars-could-replace-some-mammals-study-human-disease.

Nature, Research Communities by Springer. “Caterpillars as Alternative Animal Models for Inflammatory Bowel Disease.” Research Communities by Springer Nature, 21 Nov. 2022, communities.springernature.com/posts/caterpillars-as-alternative-animal-models-for-inflammatory-bowel-disease. Accessed 21 July 2024.

Potter, Kristen A., and H. Arthur Woods. "Trichogramma parasitoids alter the metabolic physiology of Manduca eggs." Proceedings of the Royal Society B: Biological Sciences 279.1742 (2012): 3572-3576.

Riddiford, Lynn M., et al. "Insights into the molecular basis of the hormonal control of molting and metamorphosis from Manduca sexta and Drosophila melanogaster." Insect biochemistry and molecular biology 33.12 (2003): 1327-1338.

“Sphingidae.” Wikipedia, 12 Mar. 2023, en.wikipedia.org/wiki/Sphingidae.