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Anyone who has had a meal outside can attest: flies are gross. However, they’re far more so than most people realize. Flies have been found to carry an average of two million bacteria on their bodies, and are easily able to spread this onto surfaces, food, and people simply by landing on them.

In fact, a recent hot weather spell prompted a research study in England by scientists at the University of Surrey into how much bacteria is actually carried by flies and how easily they can be spread. The results of the study were startling, as they found that if a fly has recently fed on certain dirty substances, it may carry as many as six million bacteria on its feet. Dr Simon Park, of the Department of Microbial and Cellular Sciences at the University of Surrey, performed an experiment where he trapped a number of flies in a petri dish to examine how their presence affected bacterial growth. After examining the results, Dr. Park said, “I must admit that even as a well-seasoned microbiologist, these images make me slightly queasy.”


With all this bacteria crawling on them and being left behind wherever they walk or feed, the presence of flies can absolutely lead to the spread of disease. Some of the diseases caused by the bacteria often found on flies can include:

  • Anthrax
  • Cholera
  • Conjunctivitis
  • Diphtheria
  • Dysentery
  • Food poisoning / gastroenteritis
  • Leprosy
  • Poliomyelitis
  • Trachoma
  • Tuberculosis
  • Typhoid fever
  • Yaws

It’s important to keep flies away from food, especially when there are those nearby with weaker immune systems (children, elders, and those compromised by treatments like chemotherapy), though chemical repellants can themselves be a danger. Stick with non-chemical methods such as covering food or placing devices like the ShooAway around food, which have been proven to drive away flies and other pests.