This episode is sponsored by Wren, a  website with a monthly subscription that helps fund projects to  combat the climate crisis.

Click the link in the description  to learn more about how you can make a monthly contribution to support projects  like rainforest protection programs. [♪ INTRO] Don’t you just hate it when you’re at  a picnic, about to enjoy your food, when suddenly flies begin showing up, buzzing around and landing  on your watermelon slices? House flies in particular seem to  know the exact time to crash a picnic.

But aside from being an annoyance,  are flies also a food safety hazard? Because flies usually regurgitate  some of their stomach contents when they land on something they plan on eating. And, eww.

So you might wonder if you need to  toss that picnic lunch in the garbage if you find it infested with flies. And it’s complicated, but it might depend  on what’s next door to your picnic. House flies are just one of many fly species that regurgitate their  stomach contents upon landing.

And there are multiple reasons why flies do this. First, flies have no teeth. They just have a straw-shaped mouth  that they use to slurp their food.

But first they have to make their food… slurpable. So, when they land, they secrete a bit  of digestive juices onto their food, in order to break it down. This works in a similar way to our saliva, which contains enzymes to help  break down our food as we chew.

The difference is, flies rely on the  digestive juices in their stomachs to do the chewing for them. Once it’s been liquefied, the flies are able to slurp up  the food with their spongy mouth. YUM.

Second, flies might regurgitate some of their food in order to make room for… more food. That regurgitated food hangs as a little  bubble from their straw-like mouth, which allows moisture to gradually evaporate. Then they slurp it back up in  its now more concentrated form, making more space in their stomachs for more food.

Finally, the act of evaporating  some of the liquid in their food also helps remove heat from the flies’ bodies. With all that said, the real danger might  lie with their feet, not their mouths. Because, while a fly might  not regurgitate its food immediately upon touching down, the  rest of the fly isn’t exactly sanitary.

Flies spend time on rotting food,  decomposing animals, and feces. And these can be sources of disease. E. coli, typhoid, and cholera  are among the worst cases.

Lab studies have found flies are  able to pick up and transfer bacteria even if they are only in contact with  a surface for a short period of time. And in many countries, there are  regulations in place that limit how close animal breeding facilities can be in  relation to food processing facilities. Because those facilities  are a great source of flies, and the research shows that more  flies equals more bacteria.

That said, it’s actually hard  to say how those lab numbers translate into real-life  contamination of your food. So, if several flies are  hanging around on your food, you might want to weigh the risks of getting sick against the rewards of finishing up  that sandwich you were munching on. Consider covering up your food if you’re  going to be away from it for a while, and packing a fly swatter on your next picnic.

And maybe don’t set up right next to a petting zoo or other potential source of  contamination that flies could bring in. In the end, though, we looked into it  and our research hasn’t turned up much in the way of actual illness resulting  from flies landing on a picnic. It’s your call really, but a  couple of flies on your plate are probably more a nuisance  than a public health threat.

So, could you pass the watermelon? In contrast, an unequivocally serious  public health threat is the climate crisis. That’s why Wren, a website that helps fund  projects that combat the climate crisis, is currently raising funds to provide  clean burning fuel and cook stoves for refugees in Uganda.

This project will help humans and nature  by providing over 1 million refugees with clean cooking fuel and  preventing thousands of acres of land from deforestation… per year. Once you signup to make a monthly  contribution to projects like this one, you’ll receive monthly updates on their progress. You’ll get to see the good you’re  doing and what your money is spent on.

You can start helping today  by learning more at wren.co. But you won’t be alone in this effort. We’ve partnered with Wren to plant 10  additional trees for the first 100 people who sign up using the referral  link in the description down below!

Thank you to Wren for supporting this  SciShow video and thank you for watching! [♪ OUTRO]