Here's Why You Shouldn't Worry About COVID-Carrying Houseflies

Ordinary houseflies can pick up SARS-CoV-2, the virus that causes COVID-19, and carry the virus for up to 24 hours, according to a new study. But experts say you shouldn't worry about contracting the virus from pesky bugs this summer.

The research, which was published in the journal Parasites & Vectors, featured two studies. In the first, the houseflies were tested for SARS-CoV-2 after they were exposed to milk infected with the virus. The second study analyzed samples that were tested for the virus after they came into contact with flies that had been exposed to SARS-CoV-2.

As part of the study, the researchers swabbed the inside of containers holding the flies to see if they contained viral RNA (the virus’s genetic material) and infectious virus. The swabs in the containers that held the flies previously exposed to the contaminated milk, tested positive for the virus after four hours and 24 hours, suggesting that the flies could carry and transmit the virus to other surfaces.

“Further studies are warranted to determine if housefly transmission occurs naturally and the potential public health implications of such events,” the authors concluded.

Study coauthor Jürgen A. Richt, DVM, PhD, a professor at Kansas State University and director of the Center on Emerging and Zoonotic Infectious Diseases, tells Verywell that he and his fellow researchers decided to study this because “there are many cases of COVID-19 where we don’t know how someone contracted the virus.”

Houseflies are “known to be attracted to biological fluids that can be contaminated with the virus” and are also known to transmit bacterial, parasitic, and viral diseases to humans and animals, he says. But your chances of contracting the virus from a fly are pretty slim, if not impossible.

"The research was conducted within a controlled environment and the results demonstrate that although houseflies can acquire and harbor the virus SARS-CoV-2, they do not transmit the infectious virus to other surfaces," Dana Nayduch, PhD, study coauthor and research leader at the U.S. Department of Agriculture Arthropod-Borne Animal Diseases Research Unit, tells Verywell. "Additional research is needed to test if houseflies can harbor the virus outside of a controlled environment."

How COVID-19 Spreads

According to the Centers for Disease Control and Prevention (CDC), COVID-19 primarily spreads from close contact with an infected person. People who are within six feet of a person with COVID-19 are at the greatest risk of being infected, the CDC says. When people with COVID-19 cough, sneeze, sing, talk, or breathe, they produce respiratory droplets that can be inhaled or land on mucous membranes like those that line the inside of the nose and mouth.

Sometimes, infections can spread through exposure to the virus in small droplets and particles that can linger in the air for minutes and even hours.

The CDC also states that a person could contract COVID-19 by touching an infected surface and then touching their own mouth, nose, or eyes, but that is not thought to be a common way the virus spreads.

Can Flies Spread COVID-19?

While his research was conducted in a laboratory, Richt says that it was done “in an environment which mimics normal circumstances.”

“The question we were looking to answer was ‘Can houseflies acquire the virus?’ The answer is yes,” he says.

However, their ability to spread the virus is likely limited. "The second part of our study (the transmission study) showed that flies did not transmit detectable infectious virus," Nayduch says. "All we could detect was the genome of the virus (it’s RNA) which is not infectious. We have no evidence houseflies would be important in the transmission of SARS-CoV-2."

Experts Say Not to Worry

Overall, infectious disease experts are skeptical about a fly's ability to transmit the disease. “Houseflies can carry a range of viruses and bacteria but, just because you can find that something can mechanically transfer a virus, doesn’t necessarily equate to an epidemiological risk,” infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, tells Verywell. “This is not how COVID-19 is spread.”

Adalja says it would also take a lot to mimic the experiment under normal circumstances. “How often is there milk that has COVID in it sitting out, that a fly bathes itself in, in real life?” he says. “I wouldn’t worry about this at all.”

John Sellick, DO, an infectious disease expert and professor of medicine at the University at Buffalo/SUNY, agrees. “We went through this with HIV and Ebola,” he says. “Just because you can show in a laboratory setting that you can get a mosquito or fly to have a virus after feeding on something doesn’t mean the virus spreads that way.”

Sellick stresses that COVID-19 is a respiratory virus and that the risk of contracting the virus from touching an infected surface is low. “What you can show in a lab and real-life are totally different things,” he adds.

But Richt says he’s not trying to suggest that flies are the primary driver of COVID-19. “Are flies the main way this spreads? No, first it’s respiratory droplets, then aerosols,” he says. “But flies could be a source if there is no other explanation for how someone became infected.”

Nayduch adds that, while flies may not be a crucial component in transmission, they may play another role. "While flies may not play an important role in the epidemiology of this virus and the disease it causes, we could potentially screen flies for traces of the virus and use them as sentinels to detect virus in the environment," Nayduch says.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.