Researchers found dozens of tea and herb samples contained environmental DNA from over 1,200 species of arthropods.
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Fresh cup of tea in a glass mug
Credit: Anna Janecka / Getty Images

Before eating fruits and vegetables, you're usually encouraged to wash them. It makes sense: Produce is grown outside so maybe check that a frog didn't hop into your bagged salad. (It happens!) Along those lines, some cross contamination is inevitable: The FDA even sets acceptable levels of things like insect fragments in all sorts of foods.

But recent research that looked at dried tea and herbs came back with some surprising findings of just how many bugs — or more specifically, arthropods — came into contact with these items: each sample contained environmental DNA (eDNA) from at least 200 different creatures.

The researchers from Germany's Trier University and the Max Planck Institute for Evolutionary Biology, said they chose to look at tea and herbs because they undergo less processing than other products before landing on grocery store shelves. "In a sample like coffee, which is very heavily processed, you probably have very little DNA left,"  Henrik Krehenwinkel, an ecological geneticist at Trier University, told Smithsonian Magazine, "so we tried things which were kind of as natural as possible."

In total, the study, which was published in Biology Letters, was able to identify genetic traces of over 1,200 different species of arthropods by looking at 40 samples of tea, chamomile, mint, and parsley purchased from local grocery stores. And as should probably be expected, many of the samples contained DNA from species that "could be assigned to biogeographic regions" which allowed the researchers to "reveal the geographical origins of plant samples," the paper states. "For example, many arthropods from mint tea originate in the Pacific Northwest of America, a major peppermint growing area, while typical East Asian species are only found in green tea."

But why would we want to know how many bugs have trampled all over our tea? The researchers offered plenty of practical applications. "Our work suggests that eDNA from dried plants is a useful complement to traditional monitoring, providing critical information on plant–arthropod interactions," the paper explains. For instance, this kind of analysis could be used by regulators to trace the origin of plant products. Better understanding of insect populations could aid in pest management. And this sort of research can raise awareness of biodiversity in general.

Plus, the paper opens up another intriguing possibility: Could a similar method be used to on even older samples? "Follow-up work should explore whether decade-old stored dried plant samples like herbarium specimens could also be suitable for recovering arthropod DNA," the paper states. If so, researchers could potentially peer into the past by unlocking information about change in biodiversity over the years.