NATURE HAPPENINGS - June 2005

Around the Edge of Darkness
by Damian Fagan

Hovering around the edge of dusk, a moth darts in and among the bed of Mexican evening primroses. Barely visible due to the impending twilight, I attempt to trace its path, its seemingly random flights between flowers. This moth does not labor like the others, with ponderous wings and erratic flight. No, it moves more like a hummingbird than a moth, its 3-inch long wings giving providing forward and backward movements that are punctuated by short periods of hovering.

Though it is getting dark, I can image the long proboscis of this moth probing the flowers for their sweet nectar. The plant, a member of the Onagraceae or Evening Primrose Family, has a long floral tube that requires a pollinator to posses a long proboscis to reach its nectar rewards. Sphinx moths have a 4-inch proboscis that they unfurl and slip into these floral throats. The pollinator then siphons up the sweet fluid through this tongue-like appendage, then proceeds to the next flower. When it departs, the moth carries a bit of pollen that has been dusted upon its forehead by the flower’s stamens. As the moth sticks its head into the next flower, this pollen comes in contact the flower’s style – the female structure that “captures” the pollen. The moth’s chore of pollination is done, and then repeated over and over again as it forages for nectar.

If the particular moth is a female, she may also be on the lookout for a suitable host plant. She will lay numerous eggs on the undersides of leaves. Tiny as a pinhead, the green eggs appear bolted to the leaf. When the larvae inside is ready to emerge, it enters into a world of sunshine, unless it comes out at night.

The caterpillar period goes through several molts called “instars” as the larvae consumes the leaves of its host plant. In my garden, evening primroses and tomatoes serve as luncheonettes for these voracious eaters. I once read that during wet springs when there are abundant larvae, one can hear the chewing from several feet away.

Sphinx moths and their near relatives have sleek green bodies lined with dots or marks. A fleshy process near their posterior is responsible the sphinx portion of their common name or the non-charismatic common name: hornworm. Never mind that the “horn” is at their rump, one relative of the sphinx moth gets a bad reputation due to their preference for tomato leaves. But just as the ugly cygnet turns into the beautiful swan, so too will this garden demon transform into a graceful night flyer.

After the larvae go through several growth stages, they are ready to pupate. Most crawl down the stem and burrow underground in late summer or early fall. Here they overwinter, awaiting warmer weather and the transformation into an adult. As spring rolls around, the larvae wiggle closer to the surface before they pupate. That way when the adults emerge they are just below the ground surface.

Though the adults are active mostly in the evening, they do come out in the day. These moths specialize in night blooming plants like datura, four o’clock, and evening primroses, and yet they feed on a wide variety of plants that bloom in the day. The moths aren’t selective like yucca moths, but they require flowers with high sugar contents to their nectar.

As the daylight fades and night flushes out the sky, I lose sight of these moths. With their spindle-shaped antennae and short, broad wings, I’m sure they are still out their feeding as they hover around the edge of darkness.