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Earth Notes: Sphinx Moths

A large brown moth with whirring wings drinks from a purple flower
Sphinx moth

At dusk on summer nights, white-lined sphinx moths flutter like hummingbirds around flowers of datura and evening primrose. Their dark wings bear light bands, and the underwings are cotton-candy pink. They hover above a flower only long enough to dip their long hollow tongues deep into the sugar-rich nectar stores. Then they fly off to another source, exhibiting some of the fastest flying speeds in the lepidopteran world.

The large, white, trumpet-shaped flowers of datura are often seen growing along roads and riverbanks. Each blossom unfurls for only one night, beckoning the moths like a bright beacon. By morning, the flowers spiral shut and wilt.

Sphinx moths come for the nectar, and as they feed, the females are also busy laying eggs on the leaves. In that process, they spread pollen to neighboring plants.

An egg hatches into a garish green-and-yellow caterpillar called a hornworm--named for the fleshy horn or “tail” on the back segment of the body. When monsoon rains are plentiful, these large caterpillars are abundant, munching leaves of datura and other members of the nightshade family, like tomatoes and peppers. That makes hornworms the bane of gardeners. All parts of datura are loaded with toxins, but the caterpillars can ingest them without ill effects.

Once they have their fill of greenery, the larvae burrow into the ground, overwinter, and miraculously morph into adult moths the following year. Food for the insect, reproduction for the plant—another fascinating story of co-evolution in the natural world.

This Earth Note was written by Rose Houk and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.

Rose Houk is a Flagstaff-based writer and editor, specializing in natural history and environmental topics.  Rose was a founding contributor of KNAU's Earth Notes and has written nearly 200 scripts for the series. She is also the author of many publications about national park and monuments, along with audio productions. 

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