TRR photo by Ed Wesely A syrphid fly on butterfly bush flowers. (Click for larger image)

First killing frost. Along the Delaware River near Milanville, we had a light frost on October 23 and a heavy killing frost the next morning when the mercury fell to 27 degrees.

Nasturtium and zinnia flowers drooped in the garden, as did surviving Jerusalem artichokes. Survivors included calendulas and lilac colored flower heads on a couple of butterfly bush shrubs (Buddleia).

Three cheers for Butterfly bush. These shrubs are aptly named. Once they flower in late June, their nectar is sought by squadrons of bees, moths and butterflies, whose species vary with the seasons.

Because the flowers are frost hardy, they also serve as autumn oases for migrating monarch butterflies. In the course of a big day on September 27, about four dozen monarchs refueled at Buddleia plants in our garden.

Syrphid flies. The picture above shows a syrphid fly, a little bulkier than a honeybee, extracting nectar from butterfly bush flowers on the afternoon of October 26. Its shape and colors mimic bees and wasps, as does its preference for flower nectar.

Because these beautiful, harmless flies have a habit of hovering above flowers, stationary as humming birds, they are sometimes called hover flies.

Also, because adult syrphids feed almost entirely on nectar, and because there are many species of them, they are among our most important flower pollinators.