Hoverflies

Hoverflies, or syrphid flies, are one of the most beneficial insects you can attract to your garden.

Hoverfly on carrot flower

Hoverflies are members of the Syrphidae family. There are over 6,000 species worldwide and 300 on the West Coast. Many of them mimic bees and wasps to discourage predators, but they are harmless to humans. Hoverflies mimic bees and wasps in other ways, too, as both predators and pollinators.

Poster of hoverflies (Alvesgaspar) CC BY-SA 3.0

Hoverfly description

With so much variety, there is no one description that covers all hoverflies (also spelled hover flies). They can be as large as 3/4” long or so small that you won’t notice them. They can be black or colorful, spotted, striped, or plain. What they all have in common is the fact that they tend to hover over their favorite flowers. There are some bee flies that also hover, but they are equally beneficial as both pollinators and predators, so you don’t really need to know the difference* between the two species.
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* If you really need to know the difference, hoverflies have shorter legs, a prominent beak, and a line along the back of their wings, while bee flies have longer legs, a sloping face, and clear wings.  Also, bee flies are more likely to be hairy. There. Now you know.

​Hoverfly larvae are blind and deaf. They are only 1/32 to 1/2 of an inch in length. They may be green, brown, yellow, or nearly transparent. They may have a white longitudinal stripe.

Hoverfly lifecycle

Once a female has mated, she will seek out a good place to lay her white, elliptical eggs. A good place, to a hoverfly, is one that looks like there will be plenty of aphids for her young to eat. After they hatch, hoverfly larvae hang onto a leaf with their back end and swing back and forth, looking for prey. Once found, the prey are poked and sucked dry. The larvae leave a trail of empty husks to show where they have been feeding. Eventually, the larvae create a green or dark brown pupa around themselves, where they will metamorphosis into adults.

Hoverfly larva (Katja Schultz) CC BY 2.0

Hoverfly behavior

Not all hoverflies behave in the same way, but there is enough variety to safely assume these are bugs you want in your landscape and garden. Some hoverfly larvae are saprotrophs, which means they each decaying plant and animal matter in the soil. This improves soil structure and makes nutrients available to plants. Other hoverfly maggots are powerful predators, devouring a lion’s share of aphids and other plant-sucking pests.

Hoverflies as predators

Most hoverfly species larvae will eat aphids, thrips, mealybugs, mites, scale insects, and leafhoppers. That’s a good thing, because these pests spread several diseases, including curly top, powdery mildew, black spot, rust, and sooty mold, just to name a few! Other hoverfly larvae prey on caterpillars, slugs, and codling moth larvae. In my book, there are no bad hoverflies.

Hoverflies as pollinators

As adult hoverflies feed on nectar and pollen, they also pollinate many of your garden crops. In fact, hoverflies are second only to bees when it comes to pollination. Unlike bees, which tend to prefer specific species, hoverflies are generalists, landing wherever the picking looks good.

Attracting hoverflies

There are several insectary plants that attract hoverflies. Most of these plants provide pollen and nectar to the adult forms. Hoverflies prefer plants that have shallow or umbrella-shaped flowers. These plants are often members of the Umbelliferae or Apiceae family. Adding the following plants to your landscape is sure to attract these beneficial insects:

• alliums (onion, garlic, leeks, chives...)
• buckwheat
• caraway
• carrot
• celery
• chamomile
• cilantro/coriander
• cosmos
• cumin
• dill
• fennel
• parsley
• parsnip
• sunflowers
• sweet alyssum
• tansy
• yarrow
• watercress​

Hoverfly (Thomas Bresson) CC BY 2.0

Research has shown that hoverflies prefer yellow and white flowers over other colors. Since organic pesticides, such as spinosad, also kill beneficial hoverflies, you may want to think twice about when you spray. Once flowers are in bloom, you may want to hold off.

Orchid trivia - One type of orchid, Epipactis veratrifolia, emits chemicals that mimic the alarm pheromones used by aphids. This attracts hoverflies, resulting in pollination. Stuff like that makes me wonder what else is going on that we never notice.