Blow flies can help monitor the environment

Blow flies could provide scientists with a non-invasive way to monitor the environment and important changes within ecosystems, according to a new study from Indiana University. 

The research is based on the analysis of stable isotopes, which provide important information about the diet and surroundings of any given animal. 

Study co-author William Gilhooly noted that the disruptions of climate change have increased the need for new ways to monitor animals’ environments without disturbing them.

“Blow flies are found on all continents, with the exception of Antarctica,” said Gilhooly. “Therefore, blow flies are effectively sentinels of animal response to climate change in almost any location in the world.”

More than four years ago, the researchers set out to investigate what blow flies are eating in the wild.

“We know these types of flies feed on dead animals, but until now, we really had no way of actually determining the types of carcasses they were utilizing without actually finding the carcasses themselves,” explained study co-author Charity Owings. 

Stable isotopes including carbon, nitrogen, hydrogen, and oxygen are found in the food we eat and become a part of our body through our diet. 

“When we eat a hamburger, we are getting the carbon isotopes that came from the corn that the cow was fed. Flies do the exact same thing,” said Gilhooly.

The researchers collected blow flies in Indianapolis, Yellowstone National Park,  and the Great Smoky Mountains.

“Collecting flies is easy: Have rotten meat, can travel,” said Picard. “That is it: We would go someplace, open up our container of rotten meat, and the flies cannot resist and come flying in. Collections never took longer than 30 minutes, and it was like we were never there.”

The blow flies were placed in a furnace to convert the nitrogen and carbon into a gas form. The gases were analyzed in a stable isotope ratio mass spectrometer.

“Nitrogen and carbon isotopes hold valuable information about diet,” said Gilhooly. “Animals that eat meat have high nitrogen isotope values, whereas animals that eat mainly plants have low nitrogen isotope values.

“Carbon isotopes will tell us the main form of sugar that is in a diet. Food from an American diet has a distinct isotope signature because it has a lot of corn in it, either from the corn fed to domesticated animals or high fructose corn syrup used to make most processed foods and drinks. This signal is different from the carbon isotopes of trees and other plants. These isotope patterns are recorded in the fly as they randomly sample animals in the environment.”

The stable isotope analysis was used to determine whether the blow flies were feeding on carnivores or herbivores when they were larvae.

“With repeated sampling, one can keep an eye on animal health and wellness,” said Picard. “If the flies indicate a sudden, massive of dead herbivores – and knowing what we know right now, that typically the herbivores are readily scavenged and not available for flies – it could tell us one of two things: Herbivores are dying, yet the scavengers don’t want anything to do with them as they may be diseased; or there are more herbivores than the carnivores/scavengers, and perhaps the populations of these animals has decreased.”

In Indianapolis, the majority of the blow fly larvae had been feeding on carnivores. The researchers believe this is because of the large number of animals being hit and killed by cars, making carcasses more available to the blow flies to lay their eggs.

The experts found that the larvae fed on carnivores across the national parks, despite greater numbers of herbivores. This indicates that the competition is higher to scavenge for the larger herbivore carcasses.

The study also revealed some of the impacts that humans have on the animals. The carbon isotopes of corn-based foods were present in flies from Indianapolis, as expected, but also in flies from the Great Smoky Mountains. As the most visited park in the country, scavengers have greater access to human food in the Smokies.

“This wealth of information provided by the blow flies will be fundamental to detecting changes within the ecosystem,” said Picard.

“This research has the potential to revolutionize the way biologists investigate important global issues, especially in the era of climate change,” said Owings. “Researchers will no longer be restricted to finding animals themselves, which is a daunting task; the flies can easily find the animals and then can be ‘called in’ by scientists.”

The study is published in the journal PLOS ONE.

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By Chrissy Sexton, Earth.com Staff Writer