Blister beetle 101: Your guide to a bad bug

Blister beetles give off a toxic chemical called cantharidin when stressed, which can raise blisters on human skin. It can also harm animals like horses if they eat enough of the insects while grazing.

Beetle can create blisters on skin, discomfort if eaten

This beetle was found in a package of organic spinach by a Saskatoon woman. (Darcy Parenteau)

Darcy Parenteau is worried about ever eating packaged spinach again.

The Saskatoon woman found an iron cross blister beetle while making a salad. The large red and yellow insect is about  the length of a toonie.

Apart from that, the bug gives off a toxic chemical called cantharidin when stressed, which can raise blisters on human skin. It can also harm animals like horses if they eat enough of the insects while grazing.

So, is this insect dangerous if eaten?

"Having a blister beetle in your salad probably isn't going to kill you," said Peter Warren, an entomologist with the University of Arizona. "It's probably just going to give you a bellyache. And maybe some indigestion in your digestive tract."

The blister beetles give off the toxic chemical when they are stressed, generally when they're picked up.

"It's a defense mechanism," he said. "You don't want to pick them up."

Warren said blister beetles are fairly common in Arizona, especially in vegetable patches and barley fields. 

"Wildlife is likely to stay away because of the danger colours, yellow and red," he said. "But humans are not always as attuned to the nature of their surroundings."

Ultimately, Warren said bugs in your food might not be the end of the world

"I probably have more tolerance for bugs in my food than most people do, because I'm an entomologist," he said. "Pretty much every grocery product we buy from a grocery store has a chance of having bug parts in it. And if people could just wrap their brain around that, I think they wouldn't think so much of it."


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