For most people, finding a dead fly in your cup of tea is gross. Finding a piece of it is even worse. The mere thought of insects in a beverage is enough to ruin your day — but this shouldn’t be the case here.
According to a new study, the leaves found in tea bags have likely interacted with thousands of insects before they were harvested and shipped to your local grocery store — and scientists can still find evidence of this in commercial tea bags by analyzing minute bits of DNA, a method known as environmental DNA (eDNA) analysis. According to recent research that employed this method, there were DNA traces of over 1,200 different arthropod species found in just four tea plants: chamomile, mint, tea, and parsley. You shouldn’t find this concerning, though. On the contrary, this rich presence of insect DNA in the tea is a good indicator that pesticides haven’t been used and that the tea is safe to consume.
More than 99.999% of the DNA in the tea comes from plants, and only a tiny fraction belongs to insects. So you’re still drinking tea, not insect brew — but that’s not the point. Even this tiny fraction is enough to inform scientists about the health of the ecosystems the tea is the source from, as well as the complicated route food often takes as it travels down the global supply chain to the local supermarket shelf.
This all speaks volumes about the power of eDNA analysis and its potential to augment field research in biology. The method was first employed on sediments, revealing DNA from extinct and extant animals and plants, but has since been obtained from various terrestrial and aquatic environmental samples, as well as samples from the air.
Rather than setting up insect traps in remote areas of the world, biologists can reach the same results or even find out more from the comfort of their local lab, simply by looking at the eDNA of various plants, such as tea leaves. In this case, the sampling — which is often the most difficult and time-consuming part of field research — was done by the companies that produce and ship the tea products.
Naturally, the researchers at Trier University in Germany took advantage of this situation in which all the hard work was already done for them. They simply went to their local grocery store and bought teas originating from four continents. To cover as many regions of origin as possible, the researchers purchased several versions of the same product but from different brands.
“I basically just went to a couple of different grocery stores and bought a whole bunch of different types of tea they had,” lead author Henrik Krehenwinkel, an ecological geneticist at Trier University, told Smithsonian Mag. “They must have thought I’m a pretty heavy tea drinker.”
In order to distinguish arthropod DNA from plant DNA, the researchers were able to find a key sequence that differs between them. Each tea sample contained more than 200 different types of arthropods. Not all of this arthropod DNA could be matched with known species, which again is a very good sign — it highlights the fact that we still have many species that scientists haven’t described yet.
In fact, the same method could be used for other types of commercially available dried plant material, such as spices and herbs. By piggybacking on the existing shipping infrastructure, biologists could study ecosystems faster and in farther-reaching areas of the globe than ever before. Analyzing eDNA from old plant samples collected decades ago could also inform researchers about how insect populations fared in the past and compare them to the present.
In 2022, researchers in the UK warned of an ongoing hidden insect “apocalypse”, after they found areas with high-intensity agriculture and significant climate warning had a 49% lower number of insects than in natural habitats with no recorded climate warming. Almost half of all the world’s insect species are in decline, and a third is already endangered, a 2019 meta-study found. Comparing old and new plant samples could improve conservation efforts by highlighting which regions are in trouble and in need of the most help.
The findings appeared in the journal Biology Letters.
