Identifying and Managing Walnut Husk Maggots and Flies

What Are Those Worms in Your Walnuts?

If you're hulling black walnuts and find small, maggot-like larvae inside blackened husks, you're dealing with one of two common pests: the walnut husk maggot (Rhagoletis suavis) or the walnut husk fly (Rhagoletis completa). Both are widespread across the central United States.

Identification

Adults are small, light-brown flies with two transparent wings marked by dark crossbands—smaller than a housefly. Larvae are legless, pale yellow, and grow up to ½ inch long. They feed exclusively within the husk, not the nutmeat.

Life Cycle & Damage

Flies lay eggs in nearly mature husks in early autumn. Larvae burrow in, causing husks to turn black, slimy, and adhere tightly to the shell. While the nutmeat's flavor and color are unaffected, the messy husks are difficult to remove and reduce commercial value.

Management Strategies

Cultural & Sanitation

• Remove and destroy infested nuts promptly.
• Place a tarp under the tree from July through August to catch falling larvae before they enter soil to pupate.
• Soak difficult-to-hull nuts in a damp burlap bag for a few days to loosen husks.

Chemical Control (If Necessary)

For severe or early infestations, apply malathion mixed with a bait (commercial Nu-Lure/Mobait or, experimentally, molasses at 1–1.5× the malathion rate) starting in July on a 21-day interval. Stop within one month of harvest. Spray only the lower half of the canopy when using bait.

Bottom Line

Most home growers tolerate this pest since kernels remain edible. Focus on sanitation to reduce next year's population.