It is one of nature’s great migrations: the fall migration of hummingbirds, mostly Ruby-Throated Hummingbirds, along the Texas coast. It’s an annual treat for those of us who enjoy watching these tiny and colorful birds.
On a recent morning, I was doing just that: watching the hummers fly around my deck. Then I spotted an odd one feeding at the blue sage. It was bronzy-green on the back with brownish wings, much like a Ruby-throat. As it hovered over the flowers, I saw it had a broad, white band across its back, dividing the thorax from the abdomen. It was unlike any hummingbird I had ever seen.
But wait a minute. Did I say it had an abdomen and a thorax? Those terms are usually used to describe an insect’s body regions. So I looked at the hummer again. Now I noticed it had antennae. It also was uncoiling a tube from under its head to reach into flowers. This creature wasn’t a hummingbird at all, but an insect.
It had to be a species of hummingbird moth. They are sometimes called hummingbird-mimic moths. These moths mimic not only the size and coloration of a hummingbird, but also their behaviors. The moths hover at tubular flowers and insert their long proboscis (straw-like tongue) inside to get at the nectar. And like the hummingbirds, they emit an audible hum as they go from flower to flower.
A question remains: what led to these similarities? In biology, mimicry is defined as the likeness of one species to another with the result being beneficial to one (or both) of the species. If a hummingbird-mimic moth looks and acts like a hummingbird, what is the advantage of this? Does the moth get more food if it looks like a hummingbird? Does the moth have some protection from predators if it looks like a bird? Somehow this doesn’t seem likely.
Instead, I think this similarity between bird and moth is a case of “convergent evolution.” In other words, it was coincidence. The two species evolved independently of each other. Both developed characteristics that allowed them to adapt to a similar habitat and lifestyle. They each had the same job in the same place with the same conditions. It is no wonder that they look and act alike.
Over eons of time, and in completely different time periods, certain insects and birds gained the ability to fly, to feed on nectar, and to reach deep in to flowers to get that nectar. Hummingbirds developed long tongues inside protective bills. The moths had a mouthpart that they could uncoil to suck up the nectar.
Plus, if they could hover while they take the nectar, time and energy would be saved. The ability to hover while feeding occurs in only four kinds of organisms: hummingbirds, hummingbird-mimic moths, certain bats and hover-flies. It is a behavior that gives them an edge over other nectar feeders which have to land on the flower or crawl up the plant.
Jimmy Jackson identified the moth I saw as a Clavipes Sphinx Moth. They are mostly tropical and are found only in the southernmost parts of the United States and southward. But there are over 1,000 species of sphinx moths worldwide. Anytime you see a large moth with broad, patterned wings, it is probably some type of sphinx moth.
Do you know how they got the name “sphinx” moth? It is from a peculiar behavior the caterpillars have. At their plumpest, just before they pupate, they adopt a posture that resembles the Egyptian Sphinx. The caterpillar holds its front legs off the surface and curls its head under. It is said to look like the Sphinx. It helps to have a good imagination.
To me, the caterpillars are more noteworthy for their size; they are almost 3 inches long. Most are bright green or brown and have diagonal slash marks on their sides. And almost all of them have a vertical “horn” on their posterior end. You’ve probably seen a tomato hornworm, unfortunately after it has eaten your tomato plant. Tomato hornworms are the caterpillars of a species of sphinx moth.
Uh-oh. A dilemma. Kill the hornworm that has eaten your tomato plant down to the stems. Or, let it go to pupate in the leaf litter and produce an interesting moth. It is hard to decide. I really like tomatoes.
There is one thing to say about the Clavipes Sphinx Moth. Its caterpillars feed on wild plants like Buttonbush. So it is not in direct conflict with our desire for tomatoes. But why not let them all develop into interesting moths?