Hummingbird hawk-moth (Macroglossum stellatarum) visiting a thistle. Video: gifer.com
One of the more curious insects you’re likely to run into as a gardener is the hawk moth, also called sphinx moth, a member of the Sphingidae family. There are over 1400 species found all over the world—big ones, medium ones, large ones—and what impresses most about them is their unique way of flying. Unlike the lazy movement of so many moths, they beat their narrow wings so rapidly, some up to 85 beats per second, that all you can see is a whir, often accompanied by a humming sound. This allows them to hover in the air, move forwards and backwards and travel at great speeds. Some are mistaken for hummingbirds!
This hovering capability is only known to have evolved only four times in the animal world, always in nectar feeders: in hummingbirds, certain bats, hoverflies and hawk moths. It’s an example of convergent evolution.
Hovering requires a huge amount of energy and indeed, hawk moths are heavy feeders, attracted to a specific sugary, energy-rich food: flower nectar. By hovering, they can gain access to flowers not available to other insects, often using a proboscis as long as or longer than their body to suck up the sweet liquid.
Some hawk moths are nocturnal or crepuscular, but others fly during the day, wowing gardeners with their acrobatics. For many plants, they’re important pollinators: many night-blooming plants give off heady aromas just to attract the nocturnal and crepuscular species. Think of flowering tobacco (Nicotiana sylvestris), a fairly popular annual, with its white, tubular blooms, wonderfully scented at night, but floppy and scentless during the day.
Indeed, for some plants, hawk moths are the only pollinator. The best-known case is that of Darwin’s orchid (Angraecum sesquipedale), whose white flower has a spur nearly 18 inches (45 cm) long that can only be pollinated by a specific hawk moth (Xanthopan morganii) with an equally long proboscis. The flower was discovered first, but Darwin accurately predicted that a corresponding moth would be discovered. You can read more about Darwin’s orchid and its pollinator here.
Behind Every Moth…
Yes, while the hawk moth may fascinate you and you certainly have nothing against its pollinating activities, you may have more trouble putting up with the caterpillar it arises from. Different species have different host plants (most are quite specific to certain plant species or families), but they all eat plants of some sort.
The five-spotted hawk moth (Manduca quinquemaculata), for example, prefers tomatoes. Its larva is called the tomato hornworm. (Many hawk moth caterpillars have a spike at their tip and are thus called hornworms.)
Eating people’s plants is not considered genteel behavior from a gardener’s point of view, so any hawk moth caterpillars spotted on a favorite plant (there is rarely more than one per plant) can be handpicked and disposed of or moved to a related plant of lesser value.
Hawk moth caterpillars tend to be smooth and hairless and come in camouflage shades of green or brown. Some larvae are said to mimic snakes as a protective strategy. When resting, the caterpillar often bends its head down into a praying position, like the Great Sphinx of Giza, as in the photo above, whence the name “sphinx moth.”
The caterpillars have a propensity for plants that are poisonous to other caterpillars, chewing on the soft new growth. Most then excrete the toxin, although some species retain it and become poisonous to their predators.
Hawk moths: fascinating creatures, aren’t they?