The sphinx moths are the family Sphingidae of the Lepidoptera, handsome moths that can hover in the air. Many fly by day or during dawn and dusk, so are more often spotted and admired than their relatives that fly in the dark.
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| sphinx moth pollinating vervain |
Sphinx moths adults are major pollinators, visiting flowers for nectar and carrying pollen between plants. They hover in front of flowers, the wings beating so fast you cannot see them. Few animals do that. One is the hummingbird, and the common name hummingbird moth reflects that similarity. I do not know the source of the common name hawk moth but it probably reflects the swift sure flight of these moths. Sphinx is based on the insect family, Sphingidae.
There are about 1,450 known species of sphinx moths, in about 200 genera. They are found all over the world but especially in the tropics. They are diverse and range in size from a wingspan of about 1" to 7" wingspans. Adults live a relatively long time for moths, 10 to 30 days, with a few living several moths. During that period they feed, mate, and lay eggs. Most sphinx moth adults primarily feed on nectar, and have relatively long proboscises that let them reach into flowers, making them good pollinators.
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sphinx moth, probably white sphinx moth, Hyles lineata,
feeding at catmint, Nepeta |
Sphinx moths will take nectar from a variety of flowers and flower shapes, but some flowers are specialized for sphinx moth feeding and those share a series of characteristics. The flowers are pale to white, a color easily seen at night, with a tube or a spur full of nectar. Classical sphinx moth flowers include evening primroses (Oenothera), four o'clocks (Mirabilis), columbines (Aquilegia) and tobacco (Nicotiana).
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tobacco, Nicotiana
This is a cultivated variety but the flowers
have the classical shape and color that
sphinx moths prefer |
Important pollinators shape the evolution of plant characteristics that match or take advantage of the pollinators' behavior and biology. Charles Darwin famously predicted a pollinator from the shape and size of a flower. The big white, tubular flower of the orchid
Angraecum sesquipedale from Madagascar has a nectar-holding spur that is more than a foot long. Darwin wondered in a letter what could possibly pollinate it, and predicted a moth with a foot-long proboscis! It took 150 years, but a Madagascar hawkmoth,
Xanthopan morganii, was discovered with a proboscis long enough to pollinate
A. sesquipedale, and then was indeed observed to pollinate the flower (
photos and more detail). For successful feeding by the pollinator and pollination of the plant, the two have to be a pretty good physical match. Evolving a very long nectar spur limited the insects that could take nectar from
Angraecum but increased the reward for
Xanthopan when it arrived. So long as nothing disturbs the pollinator-flower pair, such specialization works very well indeed. Most plants and most pollinators are more generalized, because each might shift in number independent of the other, so having several plants to feed from and several potential pollinators is better if (when) things change. In fact,
Xanthopan pollinates a number of related orchid species in Madagascar and southeastern Africa, and a second hawkmoth species,
Coelonia solani, has a tongue long enough for
A. sesquipedale, so even this famous system seems slightly buffered against the perils of specialization.
Sphinx moths are important enough pollinators that plants evolve the right colors and shapes to attract them. Columbine species (
Aquilegia) of the western United States range in color from red-and-yellow to blue-and-white, with solid whites, solid yellows and other variations. Miller's classic study showed that a red-flowered, nodding, odorless species
Aquilegia elegantula was pollinated by humming birds and several species of bumblebees, while the blue and white, erect, slightly scented flowers of the Rocky Mountain columbine
Aquilegia caerulea (
coerulea) was pollinated by sphinx moths and a number of bumblebees. The flowers of the Rocky Mountain columbine had evolved to better attract sphinx moth pollinators.
Miller went on to study geographic variation in flower color in the Rocky Mountain columbine, reporting a color gradient he attributed to moth behavior. At low elevations, Rocky Mountain columbine is white to pale blue, the flowers becoming darker blue at higher elevations. Its important pollinator, the white sphinx moth (
Hyles lineata photos), flies by night at low elevations; white is the most visible color in the dark. High in the Rocky Mountains, the sphinx moth is active by day because even summer nights are too cold for it. There, the columbines are blue, a color more visible by day. The gradual change in color up the mountains reflects the behavior of this important pollinator. A second sphinx moth
Sphinx vashti (
photos)
will have similar behavior,
though the bumblebees (genus
Bombus) that also pollinate it always fly by day. Recently Thairu and Brunet gave sphinx moths and bumblebees choices of columbines and artificial flowers in different colors. They found that quite consistently moths preferred blue flowers. They concluded that whatever created the increase in blue-ness up the mountains, it wasn't the white sphinx moth's color preferences. So the color gradient is a puzzle. Sitting in a mountain meadow watching sphinx moths and bumblebees visit columbine flowers is a really attractive way to do research, so we can expect future research papers looking for evidence explaining the pattern of Rocky Mountain columbine colors. Whether or not it is fun to study, the question of whether pollinator preferences or something else, maybe surface temperatures, drive flower petal colors is relevant for everything from insect-pollinated crop plants such as apples to understanding the interaction of plants with new pollinators as the climate changes.
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Colorado columbine, Aquilegia coerula from about 9000' elevation,
lower part of a range that takes it up to 13,000' |
Even as larvae, sphinx moths can be quite large and dramatic. The tobacco hornworm is the larval form of the Carolina sphinx moth, also called the tobacco hawk moth,
Manduca quinquemaculata. It is closely related to the tomato hornworm,
Manduca sexta. Both feed on plants in the tomato family, Solanaceae, tobacco, tomatoes, jimson weed (
Datura) and others. They grow into big caterpillars, 3" long, before pupating, and therefore big moths. (
Manduca caterpillar images from
Google)
The caterpillars of most species sphinx moth have a "horn" on their posterior (barely visible in the photo below
images at Google). Many are green with bright spots, some of the spots like false eyes. They are pretty easy to recognize. In North America they are among the largest caterpillars. I don't have a photo of a hornworm but here is a different sphinx moth caterpillar eating an evening primrose (
Oenothera), seen in western Nebraska.
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Sphinx moth caterpillar (likely white sphinx moth,
Hyles lineata) on evening primrose (Oenothera),
in western Nebraska |
Temperate zone sphinx moths usually have one or two generations per year, egg to larva to pupa to adult, but as the growing season gets longer, in the subtropics and tropics, they may have three or four.
Vervain, catmint, tobacco, columbine...sphinx moths will visit and pollinate flowers of many different colors and shapes. And origins. The catmint in the photos, Nepeta racemosa, a member of the mint family, Lamiaceae, was introduced from Eurasia. Our American sphinx moths are native to North America and their larvae require native plants to eat, whether tobaccos or evening primroses. The adults, searching for nectar, are not picky and will take nectar from, and pollinate, both native and introduced plants. They need numerous flowers, or ones with a lot of nectar, their only food, because flying requires a lot of energy, and hovering even more.
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white sphinx moth, Hyles lineata, feeding on dwarf catmint,
Nepeta racemosa |
Sphinx moths are a numerous and diverse set of important pollinators and really neat animals to watch.
Comments and corrections welcome.
References
Ardetti, J., Elliott, J., Kitching, I.J. & Wasserthal, L.T. 2012, 'Good Heavens what insect can suck it' – Charles Darwin, Angraecum sesquipedale and Xanthopan morganii praedicta. Botanical Journal of the Linnean Society. 169 403-432. link (Accessed 2/24/25)
Hone, D. 2013. Moth tongues, orchids and Darwin. The predictive power of evolution. The Guardian
link (Accessed 2/24/25)
Miller, R.B. 1978. The pollination ecology of
Aquilegia elegantula and
Aquilegia caerulea (Ranunculaceae) in Colorado. American Journal of Botany. 65: 406-414.
link (Accessed 2/24/25)
Miller, R. B. 1981. Hawkmoths and geographic patterns of floral variation in
Aquilegia caerulea. Ebolution. 35: 763-772.
link (Accessed 2/24/25)
Mitton, J. 2019 White-lined sphinx moth flight, agility a marvel. Colorado Arts and Sciences Magazine, University of Colorado Boulder. link (Accessed 2/24/25).
Proctor, M., P. Yeo and A. Lack. 1996. The Natural History of Pollination. Timber Press, Portland Oregon.
Thairu, M. W. and J. Brunet. 2015. The role of pollinators in maintaining variation in flower color in teh Rocky Mountain columbine, Aquilegia coerulea. Annals of Botany. 115: 971-979 link (Accessed 2/24/25)
Note: the Rocky Mountain columbine, also called the Colorado columbine and blue columbine, was registered as the state flower of Colorado as Aquilegia caerulea, but the correct name is Aquilegia coerulea. The literature is very confused; both names are in wide use. They refer to the same plant species.
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