How to Give Your Compost a Boost—with Maggots

  • The larvae of the black solider fly are tenacious eaters that can speed up decomposition in your compost pile. Photo: Mike C. //

August 7, 2015

The Allegheny Front’s Kara Holsopple has a confession to make: There are maggots in her compost pile. Really big, fat ones, like she’s never seen before. A quick internet search helped her make an ID—they were black soldier fly larvae. And like any good citizen scientist, she posted a photo of the writhing mass to It's the online grassroots almanac where people can post their questions and observations about weather and climate. Because she'd never seen them before, Kara wanted to know if these black soldier flies might be a species that we could see more in the area because of global warming.

“That's not unreasonable,” says Sandy Feather, a horticulture educator with Penn State Extension in Allegheny County. “But the winters have been bitter cold these last couple years. "They wouldn't have survived those winter temperatures so they would have had to come back and repopulate.”

It turns out black soldier flies—and their larvae—are not native to our region. But they do make it up here from more southern climates when it's warm and wet, often blowing into the area during heavy storms. They're strongly attracted to organic matter, whether that's animal manure or a compost pile. In fact, they used to be pretty common when we all used outhouses. Some farmers and gardeners even buy them because they're such great decomposers.

One of their other benefits is that they discourage the egg laying of nuisance species like horse flies—possibly by eating their eggs. In addition, adult black soldier flies don't bite, so they don’t transfer diseases.

“They’re really considered beneficial as far as manure management—particularly in confined animal-feeding operations,” Feather says.

Because they’re not likely to survive the winter in this region, home gardeners who grow fond of their decomposing skills might have a hard time keeping populations going from year to year. But Feather says gardeners could try transferring compost bins to indoor locations, like garages, in cooler months to help the bugs overwinter.

So how do you know if you have them in your compost bin? Sandy Feather says when the larvae first hatch, they’re creamy white. But as they start to feed and mature, they darken to a reddish-brown color.

“They're kind of funky looking actually,” Feather say. “When they're mature, they can be more than an inch long—maybe a little bit longer.

So what are you seeing out there? We want to know. All you have to do is go to and share your thoughts, photos or videos.