Do The Flies Buzzing Around Red Tide Fish Kills Carry Toxins? Scientists Find Out

As red tide continues to leave behind a trail of dead fish along parts of Florida's Gulf Coast, it's also drawing in "filth flies," or “blow flies.” Now, there’s a study looking at whether these flies can carry red tide toxins, known as brevetoxins.

Edwin Burgess, a veterinary entomologist at the University of Florida, said the normal flies that you might see while enjoying an outdoor picnic — the little shiny green or blue ones — are known to vector all kinds of pathogens, like salmonella and E. coli. They can cause foodborne illnesses in animals and humans.

So, Burgess wants to know if the flies swarming around red tide fish kills are picking up the brevetoxins.

"We're also looking at things like bioaccumulation, any kind of potential consequences that flies picking up brevetoxins could have further down in the food web. Lizards and birds and other terrestrial organisms eat these flies," he said.

Burgess doesn't think this would affect humans as much as animals.

"If we know that [fly populations] are exploding once red tides are happening, and they're carrying brevetoxins and they're affecting wildlife in some way, we can start to create plans that will help to mitigate the flies getting access to these tissues and contaminating themselves that would then kind of go downstream into into wildlife," he said.

But these flies aren’t just pests, said Burgess. They actually serve an “important” ecological role, too, as pollinators and decomposers.

“That's really what they're doing on these beaches in Tampa, St. Pete, is they're kind of doing their natural thing,” he said.

These types of flies also lay their eggs into decaying flesh. It will be scientifically relevant whether or not they can successfully accomplish this act within a carcass filled with red tide toxins, according to Burgess.

"If they don't carry brevetoxins, we are interested to know that as well, because it means the flies are likely using some kind of chemical or environmental indicator to show that it's safe for them to start to colonize these fish tissues. And that's an equally interesting thing," he said.

In order to do this research, Burgess and his team wear protective gear, use sweep nets to catch the flies, and then put them on dry ice to freeze them down.

“Dry ice is a very good … short-term preservative for getting samples back from the field into the lab, where we can then put them on a deep freeze, which pretty much arrests all metabolic processes and any kind of decomposition,” said Burgess.

Secondly, the group will collect any dead sea life that has larval activity and take it back to that lab to allow them grow into adults, and continue testing for brevetoxins.

“We're interested to know that at each of their life stages, if they're carrying it to that next life stage, so not only adults visiting and feeding and laying eggs, but larvae, maybe picking it up and transferring it from life stage to life stage,” he said.

The whole project will cost an estimated $6,000, coming from Burgess’ own startup fund and some outside contributors.

Burgess said he expects to have initial results in just a couple weeks, and he hopes to eventually mobilize the lab to do sampling in other states, like Texas and Louisiana, which also experience red tide algae blooms.

Copyright 2021 WUSF Public Media - WUSF 89.7