A new study takes a look at the increasing problem of frogs, rodents, snakes, lizards, birds, and even a bat ending up in people’s bagged produce.

A few years ago I wrote about all of the reasons that packaged greens are a horrible idea. Number 4 was the possibility of “free prizes” included inside. “The good news for one California woman is that she can be assured her choice of bagged salad was organic and uncut,” I wrote, “as confirmed by the live frog she found in her package of greens. After recovering from the startle, she kept the frog and named it Dave.”

You’d think stories like these are rare, right? Well it would be hard to know, since there is currently no public system to archive these incidents, write the authors of a new study taking a look at wild animals found in prepackaged produce in the United States.

Without a database recording such incidents, the scientists did what anyone else would do: They started doing online searches. They analyzed media reports and came to this conclusion:

Forty wild animals have been found in packaged produce since 2003

The 40 independent incidents of small wild animals found by customers represent four vertebrate classes: Amphibians, reptiles, mammals, and birds. Frogs and toads made up 52.5 percent of the events. Among the 21 amphibians, the most commonly identified groups were treefrogs and toads. And get this:

Seven of the nine frogs found alive by customers were treefrogs, and all but one toad was found dead.

And they note that this number is likely a significant underestimation of the frequency of such events. Here’s a table from the study cataloguing the macabre menagerie.

What is going on here?!

The story begins in the late 1980s when prepackaged produce became a staple feature of supermarkets across the country. While the rise in popularity of fresh produce in general has been a great thing for the health of the U.S. population, the skyrocketing popularity of prepackaged produce has led to some problems. Aside from all that unnecessary plastic, crops that were traditionally hand-picked, for example, became automated. The authors write:

The increased automation of farming methods combined with heightened expectations for fresh produce year-round and the fact that crop fields are not sterile environments—despite some attempts to make them so—have set the backdrop for a unique human–wildlife interaction.

And yes, that “unique human–wildlife interaction” is customers finding wild animals in their bags of salad. The automated harvesting process, combined with more agricultural land eating into natural habitat, has created a perfect storm for this bizzare scenario of agricultural collateral damage.

The study found that the rate of these unsavory surprises has been on the upswing since 2013.

Frogs appear to especially vulnerable. The study explains that “the natural history of frogs, especially their nocturnal habits and dependence on moisture due to their permeable skin, may make them more susceptible to ending up in prepacked salads over other animal groups.”

And when you think about it, it makes perfect sense. Leafy green crop fields are drenched in water and lush in vegetation – attractive habitats for frogs during dry periods.

“The modern harvesting methods for leafy greens may also have contributed to the higher frequency of frogs found in prepackaged items,” write the authors. Some greens, like baby varieties, are mechanically harvested at night when moisture levels are at their highest. “Consequently, the difficult task of detecting frogs that may be concealed in the folds of lettuce leaves has been further complicated by harvest practices that are rapid, mechanized, and conducted at night.”

One potential consequence of this – aside from the obvious trauma to both animals and salad eaters – is akin to a natural world freak accident.

At least two of the live frogs were released in non-native habitats: a pacific treefrog in Michigan and another pacific treefrog in Washington D.C. Frogs are currently in the midst of one of the greatest vertebrate die-offs of the current geological age, with the infectious disease, Chytridiomycosis, behind the decline and extinction of amphibian species across the globe. Previous research has found that the devilish pathogen was making its way around the planet thanks to to the “unintentional human-mediated dispersal of amphibians via the commercial pet trade, wars, and the global shipment of products.” The thought of this devastating amphibian pandemic being aldo nudged along by infected frogs being dispersed via ceasar salad mix is unsettling, at best.

Surprisingly, the research found that wild animals were found less frequently in organic products – one might think that organic fields would be more inviting – however, the researchers’ data did not factor in the relative rates of incidents per total acreage of organic versus conventional produce. That is, there’s a lot more conventional produce grown, and so more opportunity for accidental stowaways.

One of the things that the authors explored was the food safety risk of small animals mingling with food (they didn’t find much). Feral pigs and livestock runoff are just a few of the causes of tainted produce causing foodborne illness. The current method of negating such risks is with what the authors describe as the “scorched earth” approach; basically, removing nature from the fields. They suggest such an approach is futile, aside from not being very effective.

The solution, the authors say, is a radical idea in the face of feeding more people than ever, of increasing consumption and agricultural amplification:

“Rather than striving in vain to attain an entirely sterile growing environment (i.e., the currently employed ‘scorched earth’ approach,) growers should embrace more sustainable policies that attempt to non-lethally reduce the most salient risks of a wildlife-related incident.”

They say that the answer is not in trying to control wildlife, but in better studying a wider segment of biodiversity near farms, in order to better develop methods to minimize the risks.

As Tom Waits sings, “you can never hold back spring” – and you can’t keep a frog out of a lush baby-arugula rain forest.

The study, There’s a frog in my salad! A review of online media coverage for wild vertebrates found in prepackaged produce in the United States, was published in Science of The Total Environment.