Some winters ago a low-grade creeping panic set in at our house in the form of a bug we did not recognize. This winter I’ve noticed a lot of images of this bug posted online, with apparently similar dismay. So let me tell you the story.

At first we thought they were aliens.

Long spindly legs. An abdomen like a squared-off arrowhead. A sticklike head out of a science fiction movie. They lumbered lonely along countertops then fluttered away in drunken V-trajectories sounding like toy outboard motors.

“Where is it now?”

“Don’t let it land on me.”

“What are these things, anyway?”

A Western conifer seed bug. Photo by Dana Wilde

This last question worried us because the first time we noticed them we had just returned from living in mainland China. What if these bugs had stowed away in a suitcase in Xiamen, traveled with us to Maine, propagated to tens of thousands, and were set to decimate North America’s ecosystem?

The real shock came when we killed one, which was not hard to do because they move like they have a load in their pants. I slammed one with a folded-up magazine as it paused along a margin of the bay window, hoping it wouldn’t splatter. It didn’t. In fact it did not even seem crushed. It just dropped to the sill among the geraniums. Then came the alarm: It stank. Bad. A sharp, sour odor, like pine pitch gone rancid in the refrigerator.

Naturally, we started calling them stink bugs.

As March labored into April, we saw fewer of them and thought maybe these Chinese stink bugs were unable to adapt to the lengthy Maine cold and died out. Maybe we would not be responsible for an ecological holocaust after all.

We more or less forgot about them. Summer came and went, as usual, in about four days. Then in October, the bugs started appearing again, on couch cushions, bedspreads, Bonnie’s head — buzzing in the night. Appearing like lugubrious wraiths on the kitchen table.

We kept calling them stink bugs and avoided killing them. I developed a technique of herding the invader onto a sheet of paper, then flicking it out the door. Bonnie’s students recognized her description and said they called them “pine bugs.”

It seemed impossible that I could have lived in Maine (with sojourns in China and the Balkans) for nearly 50 years without noticing a house bug that seemed so common. So I did what every backyard naturalist does in the 21st century — I looked for pictures on the internet.

It turned out they are not a stink bug, but one of its relatives in the order Hemiptera, also known as “true bugs,” which includes water striders, damsel bugs, ambush bugs, stilt bugs, assassin bugs, bed bugs, and thread-legged bugs, among others. The true bugs invading our house were leaf-footed bugs, family Coreidae. The cartoon-character species of leaf-foots at our house, and whose pictures alarmed people have been posting online lately, was Leptoglossus occidentalis, the Western conifer seed bug.

The reason we never saw them before 15 years or so ago is not because they came from China or Zeta Reticuli, but because they’ve been moving eastward in recent decades from their original range around the Rocky Mountains, inspired by milder winters, aka climate change. They appear in the house during cold weather because they’re looking for a warm place to wait for spring.

They stink when you damage them, but they feed on the cones of pines and firs, not human flesh, so they’re harmless to us. (Though one did nip me once, an apparently very rare occurrence.) Still, it’s unsettling to find one in the chicken soup pot (which I did once) or scaling Bonnie’s shoulder (which I did not tell her, I just hugged her with a sweeping hand, thinking what warmth the bug had brought in that way). What a nuisance.

Dana Wilde lives in Troy. You can contact him at naturalist1@dwildepress.net. His book “A Backyard Book of Spiders in Maine” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.