This week a pair of exquisite creatures arrived at Bug of the Week. The first was an enormous scary caterpillar discovered in a residential landscape. Bedecked with strange orange and black horns and almost half a foot in length, the hickory horned devil takes the prize for the largest caterpillar in Maryland. This behemoth grew from a small larva that hatched from eggs deposited several weeks ago on tree. Plants most commonly selected as food for the young are those in the walnut family such as walnut, butternut, and hickory, but larvae also occur on ash, beech, lilac, persimmon, sumac, and sweet gum among others.
The caterpillar featured in this episode is almost fully-grown and will soon leave its host, descend to the ground, and burrow in the soil or leaf litter. There it constructs a cell in which it will pass the winter as a pupa. In spring, the gorgeous adult, known as the regal moth or royal walnut moth will emerge and alight on nearby vegetation. The female releases an irresistible scent called a sex pheromone that attracts a hopeful male. If the match is mutually acceptable, they mate and within a day or two, the female deposits dozens of eggs on a suitable tree. Adults do not feed and live only a few short days, but caterpillars require several weeks to develop. The hickory horned devil occurs from Florida to New England. In southern states, two generations of this beauty occur each year and in the north, only one generation completes development each year.
Our second guest this week is the fascinating and energetic hummingbird moth. Hummingbird moths are beautiful insects as both adults and larvae. The adult flies very rapidly to a blossom, inserts a long, straw-like proboscis into to the flower, withdraws nectar in just a few seconds, and flies to the next feeding station. The proboscis or “tongue” of the hummingbird moth is a remarkable structure and in some species, this appendage reaches astonishing length. Charles Darwin discovered an orchid with a nectar receptacle almost a foot from the tubular opening of the flower. He predicted that a species of pollinator with an exceptionally long tongue must have evolved to service the orchid. Although Darwin never observed the pollinator, his prediction proved correct many years later with the discovery of a giant hawk moth, Xanthopan morganii praedicta. Its tongue is more than nine inches long and it is the putative pollinator for the Malagasy orchid. Returning to our hummingbird moth, its favorite flowers are honeysuckle, snowberry, lilac, phlox, bee balm, trumpet vine, vetch, butterfly bush, and thistles. Its amazingly long proboscis allows it to reach deep inside tubular flowers to drink nectar.
Unlike its cousin the regal moth, the hummingbird moth feeds often and likely lives for weeks. In addition to feeding like a hummingbird, some say that the greenish hairs on the back of the moth resemble feathers of a ruby throated hummingbird. While a tasty moth might make a fine meal, a predator might think twice about eating a hummingbird. Hummingbird moths are found throughout the United States and venture as far north as Alaska. Hemaris thysbe has two generations in southern states and one in its northern range. A close relative of the hummingbird moth is the snowberry clearwing, Hemaris diffinis. I was fortunate to discover a caterpillar of one consuming leaves of honeysuckle. As you see, it bears a horn on its tail and, like the hummingbird moth, belongs to a family known as sphinx or hawk moths the larvae of which bear the name hornworms. We visited the tobacco hornworm in a previous episode of Bug of the Week. So, next time you see a hummingbird at a thistle or butterfly bush, look twice, you may have an unexpected surprise.
Bug of the Week thanks Bonnie Deahl for sharing the image of the hickory horned devil and Paula Shrewsbury for the image of the hummingbird moth that served as inspiration for this episode. Two marvelous references “Darwin’s Madagascan Hawk” by Gene Kritsky and “Caterpillars of Eastern North America” by David Wagner were references for this Bug of the Week.