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that helps fund projects to combat the climate crisis.
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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.
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 liquified,
the flies are able to slurp up the food with their spongy mouth.
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 cookstoves
for refugees in Uganda.
This project will help humans and nature
by providing over 1 million refugees with a 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!
This episode is sponsored by Wren,