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Of Assassins, Soldiers, Damsels and Hovercraft: Four Beneficial Insects

This is an abridged version of the article written by Darrell g.h. Schramm, U.C. Master Gardener, Solano County from the Solano County Master Gardeners Spring 2010 Newsletter, “Seeds for Thought.”    Click here to read the full article.

As the inhabitants of our injured world move increasingly from less toxic to non-toxic methods in agriculture and gardening, it is vital to be informed of insects in our landscapes that are beneficial to us. Spraying and fertilizing with toxins has too often destroyed our allies along with our enemies. If we recognize and befriend insects that are good for us, we may need not to work so hard on those that are against us. Among the beneficial insects that assist us in garden, landscape, and crops are the assassin bugs (Reduviidae), the soldier beetles (Cantharidae), the damsel bug (Nabis spp.), and the syrphid fly (Syrphidae)—also known as hover fly or flower fly.

Several types of assassin bug inhabit the West, the most common being Robust Assassin Bug (Apiomerus spp.), Spined Assassin Bug (Sinea diadema), and Leafhopper Assassin bug (Zelus renardii). These long-legged insects have a small head with bulbous eyes and a syringe-like beak with which they inject a poison into their captured prey. While the adults do not fly well, they—like the nymphs—move quickly when disturbed. While they feed on many insects, they feast significantly on aphids, caterpillars, leafhoppers, asparagus beetles, Japanese beetles, and, regrettably, the beneficial lacewing. Some prey on termites.

If you wish to attract assassin bugs, grow Queen Anne’s lace, plants of the carrot and of the daisy family, goldenrod, alfalfa, oleander, and/or camphorweed. Provided you do not use toxic sprays, a combination of these plants is sure to host them. In the fall they seem to prefer yellow and white or all-yellow flowers.

spined assassin bug

An adult spined assassin bug. Photo by Jack Kelly Clark.

The adults of the damsel bug are long, slender insects as well, about two-fifths of an inch, typically matte brown, grey, or somewhat yellow-tan. The body looks rather like a long, false fingernail. The head is somewhat like that of the assassin bug, small with bulbous eyes; the antennae are quite long. The nymphs look similar but are shiny in hue, unlike the adult. Both move swiftly when disquieted or stirred by outside stimuli. Tree crops, row crops, and roses welcome them. Why? Because they feed on aphids, small caterpillars, leafhoppers, mites, thrips, and other bugs.

Like most beneficial insects, they prefer tiny flowers that offer both nectar and pollen. Some of the flowers that attract them are the following: coneflowers, sunflowers, daisies, asters, and cosmos; angelica, fennel, yarrow, and dill; lavender, goldenrod, hyssop, and other spiked flowers; evening primrose, poppies, and buttercups. Plant any of these generously, and the damsels will help you in your distress.

damsel bugs

damsel bug adult (top) and nymph (bottom). Photo by Jack Kelly Clark.

Soldier beetles help keep enemy pests in check and also pollinate. These half-inch, narrow insects sport flattened, leathery but soft wings covering their backs. Usually dark brown or black, sometimes grey, the wings contrast with the orange, red, or yellow head. Soldier beetles have long, thread-like antennae. Generally hatching in the spring, the larvae are dark, flat, and multi-segmented, the head rather rectangular and usually deep blood red. In litter, in soil, or under bark, they feast mostly on the eggs and larvae of beetles, grasshoppers, moths, and—sadly—butterflies, as well as on root maggots, aphids, and mites.

Want to attract them? As pollinators, they favor cluster-flowered plants in the sunflower and umbel families, such as milkweed, fennel, yarrow, goldenrod, and cosmos. They prefer a moist habitat. If you grow these plants, keep them watered to keep the soldiers around.

soldier beetle

Adult soldier beetle. Photo by Jack Kelly Clark.

The syrphid fly is one of few insects that can fly backwards. Reminiscent of a honeybee, it wears black and yellow crossbands around its abdomen.  Drawn to aphids in gardens, landscapes, and agricultural sites, the females lay their eggs near or in colonies of aphids. The whitish or grey eggs, oblong and generally found lying on their sides, metamorphose into legless larvae that appear maggot-like, usually with a yellow stripe on the back from the tapered head to the toe. Up to a half-inch in length, they show a translucent skin that reveals internal organs. It is when syrphid flies are in the larval stage that they feed on insects—primarily plant-eating insects. One syrphid larva can consume hundreds of aphids a month.

California lilac (ceanothus), asters, buckwheat, fleabane, helianthus, roses, and slender sunflowers attract the fly. But they also feed on aphids found on citrus, grains, corn, alfalfa, grapes, lettuce and other vegetables. They do not sting. Welcome them.

Syrphid fly larvae on rose. Photo by Jennifer Baumbach.

Want to  learn more?  The Integrated Pest Management Program online has a fantastic gallery of beneficial insects.

Haggard, Peter and Judy. Insects of the Pacific Northwest. Portland, OR: Timber Press, 2006.
Lavoipierre, Frederique. Garden Allies: Soldier Beetles. Pacific Horticulture. July 2008.
UC IPM Online. ‘Pests in Home, Garden, Landscape and Turf: Natural Enemies Gallery.’


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