If you find these walnut-like growths on your Christmas tree, “don’t bring them in.”

It’s that time again when people cut down live trees and bring them indoors to hang plastic decorations to celebrate the birth of a man who may have been born in April.

Although real trees are slightly better for the environment than plastic artificial trees, it’s best to check them over a bit before bringing them indoors. Small walnut-like growths sometimes found on Christmas trees are not part of the tree itself, but “oothecae” that may house hundreds of praying mantis eggs, one family has discovered.

Andrea Coward from Ohio, USA, and her family decided to cut down a tree from a nearby farm. Two weeks later they noticed movement between the branches and needles.

“They were on the branches of the trees and then they just started running,” Coward said in an interview with Inside Edition. “They ran down the tree, across the ground and just scattered everywhere.”

According to a Facebook post from officials in Erie County, Ohio, if you see such growth on your tree, the best advice is not to bring it indoors.

“PSA: If you happen to see a walnut-sized/shaped egg mass on your Christmas tree, don’t worry, cut the branch and place it in your garden,” they wrote in the post. “That’s 100-200 praying mantis eggs!”

Of course, this advice only applies to people living in areas with praying mantises, and the danger is to the praying mantises themselves. The creatures are completely harmless to anyone other than their prey, which – fortunately – we are not.

“Don’t bring them in,” the post says, “they will hatch and starve!”

Even with their rare, venomous bites, they are unlikely to pose a threat to humans and do not transmit disease. The praying mantis, on the other hand, would be at serious risk of food shortage if it were brought into a nice, cozy, insect-free living room at Christmas.

Of course, in areas where praying mantises live, Christmas tree farms will try to keep an eye out for these bags.

“We train our workers to look for them as we process the trees our customers cut in our fields,” Alan Binger, owner of Hidden Pines Christmas Tree Farm in Ohio, told The Dodo. “We put each tree on a shaker after felling, which sometimes separates the bag from the tree, but other times we pull the bag off the tree manually. We save any bags we find and place them back in smaller trees in the field so they can hatch in the spring and do their great work.”

However, if they are missed, Ohio officials suggest that you simply cut the branch and place it outside before witnessing up to 200 praying mantises crawl out of their eggs.

An earlier version of this article was published in December 2021.