Mystery Fly Plagues Terrapin Nests

Turtle nests have many predators: red foxes, raccoons, skunks and flies. How much damage can a fly do? A good deal when it’s in its larval form—or a maggot.

Maggots have been associated with many diamondback terrapin nest failures over the years, though it’s not clear whether maggots actually target healthy nests or are  attracted to damaged/dead eggs.

Which fly is it? (photo by Karen Strauss)


Because diamondback terrapins are listed as a threatened species in Massachusetts, terrapin team field leader Ronald Kielb Jr. and veteran volunteer Karen Strauss wanted to learn more.

Their first objective was to determine which species of fly they were dealing with. Last fall, they collected some pupae from a turtle nest on Indian Neck.  Later, Ron managed to get adults to emerge in the wet lab. He then contacted an expert on sarcophagid (flesh-eating) flies at the Smithsonian Institution who was unsure about the species and referred him to Thomas Pape, a world authority at the University of Copenhagen.


These fly pupae are typically found near the top of a terrapin nest.


“Dr. Pape asked us to mail the flies over to him,” Ron says. This proved to be easier said than done. “The clerks at the post office were perplexed when I said I would like to send some flies to Denmark”.

The lab samples had been fixed in ethanol which is banned by the US postal service for any packages that require air flights. So Ron removed the flies from their liquid preservative and placed them in small tubes which were double bagged. Then there was the matter of what to declare on the customs form.

“Should I just write ‘dead flies’?” he recalled asking. Ultimately, that’s pretty much what he did do. ” I was instructed to write ‘Dead flies for scientific research. No commercial value’.”

This week, Ron received an answer from Dr. Pape, who was able to identify the fly species: Tripanurga importuna . He also forwarded a paper submitted by Canadian scientists in 2007 which concluded that these flies primarily are drawn to dead tissue but will on occasion go for live embryos and hatchlings too.

So what have we gained from this project?  Science coordinator Mark Faherty says it’s the nature of scientific inquiry to investigate something

for its own sake because you never know what might end up being useful in the future. “It’s pieces of the puzzle,” he says. But Ron is hoping for more.

“Now that we know what fly it is,” he says, ” maybe we’ll get a better understanding of its ecology which could lead to experiments for ways to better protect our terrapin nests.”

First terrapin nest of the year on Lieutenant Island (photo by Ronald Kielb)



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