Video: Identifying Syrphid Fly Larvae: Important Beneficial Insects in Controlling Aphids

eOrganic author:

Carmen Blubaugh, Washington State University

This eOrganic video was created by members of a project of the USDA National Institute of Food and Agriculture, Organic Agriculture Research and Extension Initiative (NIFA OREI) entitled Biodiversity and Natural Pest Suppression (BAN-PestS). 

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Video Transcript

Syrphid flies, also known as hover flies, are beneficial insects. The adult fly lays its eggs on leaves near aphid colonies. As adults, they are important pollinators feeding on a wide range of flowers. In their larval stage, they prey on aphids. Each larva that hatches can consume hundreds of aphids. Syrphid fly larvae are aggressive aphid predators. They are commonly considered to be the most important aphid predator in vegetable crops.

Identifying Syrphid Flies

There are many species of syrphids. The adult flies are usually yellow and black and thus resemble bees. However, like other flies, they only have one set of wings. As their namesake indicates, they can often be seen hovering above flowers or aphid colonies. The eggs resemble a grain of rice and are often laid singly on leaves.

The larvae are frequently confused with common caterpillar pests that feed on vegetable crops. Being able to distinguish between the caterpillar pest and the beneficial syrphid fly larvae is crucial as you make decisions about pest management on your farm. Luckily, there are a few simple features that will allow you to distinguish between syrphid fly larvae and caterpillars. The first thing to look for is whether or not the insect has legs. Syrphid fly larvae do not have legs and move in an undulating manner. Caterpillars have legs. If you are unsure if an insect has legs, try getting the insect to move. The legs will be apparent on a moving caterpillar.

Syrphid fly larvae have nondescript heads, no eyes, and no chewing mouthparts. Caterpillar pests have distinguishable heads with chewing mouthparts. Impressively, these blind legless syrphid fly larvae manage to consume entire aphid colonies. These are valuable creatures to respect and support on your farm.

Promoting Syrphid Flies on Your Farm

You can make your farm more hospitable for syrphid flies by planting flowers that provide nectar for adult flies, such as sweet alyssum. Studies in apple orchards and collards have shown that planting sweet alyssum greatly increased the population of syrphid flies, leading to reduced aphid infestations (Gontijo, Beers, & Snyder, 2013; Ribeiro & Gontijo, 2017). Research out of California has looked at how to most efficiently intercrop sweet alyssum to attract aphid predators to lettuce fields. Their work indicates that as few as 1 to 2 alyssum transplants per 50 lettuce transplants is sufficient (Brennan, 2015). 

Syrphid flies are an important aphid predator and pollinator to promote on your farm. Knowing a few identifying characteristics—no legs, eyes or chewing mouth parts—can help you distinguish these beneficial insects from caterpillar pests. Being able to identify these insects will assist you in making pest management decisions that support these important predators and pollinators.

Follow this link to find a user-friendly flier that will help you distinguish between specific syrphid species.

References and Citations

Published July 13, 2017

This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.