The Mystery of the Mushroom Flies

October 10, 2017

“We can do great things with the help of citizen scientists who extend our reach into urban areas that are generally off-limits,” said Entomology Curator Brian Brown, after he and then-Assistant Collections Manager Emily Hartop got a call out of the blue one day in April. That call was from the proprietor of a bed and breakfast in Los Angeles not far from the Natural History Museum of Los Angeles County. The B&B had some mushrooms growing in their yard that had flies all over them. Would the entomologists care to come and take a look?

Brian Brown had wondered about these little flies that often cluster around mushrooms for 30 years, but he had never been able to identify them. He could tell they were phorid flies, but identifying the exact species had proved tricky. To do that he would have to carefully inspect the male 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 find them.

Meanwhile, all around the Los Angeles area, the BioSCAN Project, in which community volunteers host insect traps in their yards and gardens, had been well underway since 2012 and NHMLA scientists were discovering many new species of phorid flies. Among those new discoveries was Megaselia marquezi, a newly identified species that was named by Hartop and Brown after the Marquez family, citizen scientists who hosted a Malaise insect trap in 2014 in the Union Avenue / Cesar Chavez Community Garden. Even though these flies were frequently found in the area, the scientists had only been able to observe them after the male flies had been collected in traps, so the rest of their life cycle remained a complete mystery.

photo of Jesus Marquez standing in a garden
Jesus Marquez at the Union Avenue / Cesar Chavez Community Garden, where he and his son, Humberto, hosted a Malaise trap for the BioSCAN Project in 2014.  The citizen science efforts of the Marquez family led to the discovery of a phorid fly that was named Megaselia marquezi in their honor.  photo: Kelsey Bailey


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

So, back to the mysterious mushroom flies. After that phone call, Hartop and Brown studied the fly-covered mushrooms at the bed and breakfast, and were able to observe the female flies laying their eggs (which is called ovipositing) between the gills of the mushroom caps.

Inside the mushrroom cap are fly eggs, carefully laid in between gills.

After the eggs hatched, the larvae then developed as they fed on the fungi. Eventually, the larvae left the safe harbor of the mushroom to pupate (like butterflies in their chrysalises) in the soil before emerging as adult flies to start the process all over again.

It was the just-hatched (the scientific term is teneral) males that Brown was finally able to collect and use to confirm the species. And, to his surprise, they were the BioSCAN’s widely collected Megaselia marquezi!

The connection of these two discoveries about the life cycles of these tiny flies is not just a win for entomology but also for citizen science — the fruitful collaboration of researchers and the public. So, now there is one more Megaselia marquezi mystery to solve: Where do the adult male flies hang out after they emerge from the soil? Hopefully, some day another curious citizen scientist will lead our entomologists to the answer!

The study is published in Biodiversity Data Journal.


(Posted by: The Citizen Science Program)

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