Yep, that greenish "dirt" on your kale is caterpillar droppings
What you see: A greenish brownish, maybe wet "dirt" on your kale leaves What it is: Caterpiller poop Eat or toss: If the kale is otherwise healthy looking, give it a gooooooood rinse, and then eat. Trim off any nibbled on areas. If the caterpillars have really sabotaged the rest of kale, leaving lots of holes, discoloration and rotting areas, dump it.
The story: Witness the very hungry caterpillar in real life. It chews ragged holes into crops like kale (and broccoli and cabbage), digests the leaves and then, this was left out of the popular children’s book, excretes little bundles of poop salad.
In this case, you’re probably looking an imported cabbageworm, which is eating voraciously as it prepares to transform into a little white butterfly.
So, obviously you’re not going to eat the caterpillar excrement and you’ll want to wash it off with an aggressive rinse (and not just a water soak). But, once you’ve done that, can you be certain that the kale is still good to eat?
I posed the question to Don Schaffner, a microbiologist at Rutgers. He noted that he had never seen reports of human disease outbreaks traced to caterpillar feces, or any kind of insect feces for that matter. The scientists looking out for the safety of our food system are more concerned about flies who land on animal excrement and then on human food, than the feces the insects themselves are leaving behind.
“It’s probably more a theoretical yuck factor,” he said of the kale pictured above. “I can’t think of any reason why it would be especially risky but I can certainly think of loads of reasons why nobody would want to eat it."
Trim chewed areas
The greatest potential risk comes not from the excrement, but from the areas the caterpillars have been feeding on. If they’ve damaged part of the leaf, microbes, possibly some human pathogens, could move in. So while a thorough rinse is sufficient to get rid of the caterpillar’s leavings on healthy parts of the kale, you’ll want to trim off any areas that they’ve nibbled.
“You’re consuming the clean and intact part of the plant and that should be fine,” said Ric Bessin, extension entomologist with the University of Kentucky.
If the kale is riddled with chew holes and is looking discolored and sad, maybe even getting soft and slimy all over, then you’ll want to say goodbye to the whole thing.
Another fun fact: insects like these caterpillars are cold blooded and can survive low temperatures. So while the fridge may slow them down, they’ll keep eating and pooping in your crisper drawer. If you spot some bugs in your fresh veggie haul, consider cleaning and drying the produce to remove creepy crawlers before you stash it in the fridge.
A tricky balancing act
Bessin pointed out that when it comes to minimizing both insecticide use and kitchen insect encounters, farmers face a tricky balancing act.
“I hear from consumers on both sides of the issue,” he said. “Some would rather have less pesticide and put up with a little more damage. Others don’t want to be bothered at all with the pests. They see it and it turns their stomachs and they don’t want to eat the produce.”
Jeffrey Hahn. Extension entomologist. College of Food, Agricultural and Natural Resource Sciences. University of Minnesota. Don Schaffner. Microbiologist. Extension Specialist in Food Science and Distinguished Professor at Rutgers University. Featured Creatures: imported cabbageworm. John L. Capinera. University of Florida, Entomology and Nematology. Imported cabbageworm. Missouri Botanical Garden