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Home > Research & Collections > News > Mysterious Mushroom Flies

Mysterious Mushroom Flies

The lifecycle of a secretive fly is revealed

A close-up of a female Megaselia marquezi by Emily Hartop.

Entomology Curator Brian Brown had known about them for 30 years — these little flies that often cluster around mushrooms. But he had never been able to identify them. He could tell they were phorid flies, but identifying the exact species is tricky. To do that you have to carefully inspect the males’ genitalia under a microscope. And that was the problem: only female flies were ever found buzzing around the mushrooms. Where were the males? No one could ever find them.

a closeup photo of the inside of a mushroom, with oblong eggs laid inside it
Inside the mushrroom cap are fly eggs, carefully laid in between gills.

Brown and then-Assistant Collections Manager Emily Hartop got a call out of the blue one day in April that would lead them to the answer. It was the proprietor of a bed and breakfast in Los Angeles not far from the Natural History Museum of Los Angeles County. They had some mushrooms with flies all over them. Would the entomologists want to take a look?

At long last, Brown and Hartop found the well-hidden males and could then identify this mysterious fly — it’s Megasela marquezi. This particular species is the sixth most commonly collected species in the Los Angeles area in the BioSCAN Project, where volunteers host an insect trap in their backyard. But even though this fly is commonly found in the area, its life cycle had been a complete mystery, so no one knew it was this species that had been seen around mushrooms for decades.

a photo of a man standing in a garden smiling
The fly was named by Hartop and Brown after the Marquez family who reside in the Pico-Union district of LA. Jesus and Humberto Marquez, a father/son team, help manage the Union Avenue / Cesar Chavez Community Garden where they hosted a Malaise trap for the BioSCAN Project in 2014.

Now we know the females lay their eggs (which is called ovipositing) between the gills of the mushroom caps, where the larvae develop as they feed on the fungi. Eventually the larvae leave the safe harbor of the mushroom to pupate (like butterflies in their chrysalises) in the soil before emerging as adult fies to start the process all over again.

It was these recently hatched (the scientific term is teneral) males that Brown was able to use to identify the species. Where the adult male flies hang out remains a mystery.

Peering into the secretive life of these tiny flies is a win not just for entomology but also for citizen science — the fruitful collaboration of researchers and the public.

“We can do great things with the help of citizen scientists who extend our reach into urban areas that are generally off-limits,” said Brown.

The study is published in Biodiversity Data Journal.


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