By LESLIE BISHOP, guest columnist
“Look at that beautiful butterfly!” my friend said as we watched the dogs playing in the garden.
On close inspection, I saw that the butterfly was really a moth.
The moth was resting with its large, dark, velvety wings open on a sedum plant, and I could easily see its long, feathery antennae and stout, fuzzy body and legs. Butterflies have thin antennae and slim, smooth bodies.
Both moths and butterflies belong to the insect order Lepidoptera and share the characteristics of two pairs of wings covered in minute scales as well as complete metamorphosis.
This particular moth was a Promethea Moth, a type of giant silk moth in the family Saturniidae. These large moths are characterized by bright eyespots on the upper rim of the dark forewings and white, crescent-shape spots on both forewings and hindwings.
Our moth was a male, much darker than the toffee-colored females, and he must have just emerged from his cocoon because his wings looked so perfect. His only job now is to find a mate, and he was probably in the process of doing so when we found him.
If he is lucky, somewhere within a mile radius a female Promethea Moth will be releasing pheromones from a gland in her abdomen. This olfactory plume can be detected by our male by specialized sensory cells located on his feathery antenna. He will follow these airborne chemical signals along a concentration gradient directly to the female.
Unlike other moths, the Promethea Moths mate during the day instead of night. Finding a mate quickly is vital; these moths have only vestigial mouthparts and do not feed. They can live for several days on energy stored from caterpillar fat.
Later in the evening, after mating, the female will lay a cluster of eggs on the leaves of a host plant, which will provide immediate food for the leaf-crunching caterpillars when they hatch. The Promethea Moth uses a wide selection of woodland plants as hosts, including sassafras, spicebush and tulip tree.
The caterpillars grow and shed their skin (molt) in several stages (instars). After their final molt, these handsome green caterpillars with black dots have red tubercles protruding from their heads and yellow ones on their rears. Their salivary glands are modified into silk glands, and the Promethea Moth caterpillar uses this strong silk to build a protective cocoon. The caterpillar will reinforce the attachment of a leaf stem to its branch and then line the leaf with silk. Then the caterpillar will roll the leaf around itself like a burrito and seal up the crease with silk. Within this protective silken leaf cocoon, the caterpillar will pupate. To see photos of all the life stages and videos of behavior, check out this website: performance-vision.com/promethea-2010.
In Indiana, Promethea Moths have two reproductive periods. The moth we found completed metamorphosis and reproduced in early June. He overwintered as a pupa in his silken cocoon. His offspring will reproduce this summer and their caterpillars will pupate. The adult moths will reproduce in the early fall. The caterpillars that result will become pupa that overwinter.
Biologists found that several species of Saturniidae moths, such as our Promethea Moth, have biological clocks in their brains that can detect day length. When their brains detect the shorter days of fall, then the caterpillars’ pupae will go into a state of diapause, or suspended development, in order to overwinter. When their brains detect the longer days of summer, their pupa will complete development.
These beautiful Promethea Moths, along with other large Saturniidae moths such as the Luna Moth, Tulip Tree Moth and Polyphemus Moth, used to be quite common in our deciduous woods. Now it is rare and exciting to observe these spectacular moths in nature. Biologists have determined that their rarity is due to attempts to control gypsy moth caterpillars such as the use of Bt (Bacillus thuringiensis) and the introduction of a tachinid fly parasitoid. These attempts at biological control of an insect pest have had the unintended consequence of also harming benign caterpillar species.
When I come across such a beautiful moth as Promethea, I feel I have received a gift. And this gift is even more delightful when shared with a friend.
