The creature stole across the painted rocks on the lakefill. She did not know what it was, and even though it was about 6 a.m., she texted the photo she took of the animal and sent it to a friend. His response: “American mink.”

The American mink (Neovison vison) is not only common in northeastern Illinois but are widespread in Canada and the United States. The head-body length of the adult mink is between 12 and 17 inches; the tail adds another five to nine inches to the measure, according to information posted on the website of the Illinois Department of Natural Resources, https://www2.illinois.gov/dnr. Minks have small ears, and the toes have webbing at the base. Red-brown fur on the body darkens at the tail, the last third of more of which is all black.

Minks tend to be active at night, “So, generally speaking people don’t see them around much. And they’re small and they’re dark and they can hide in the shadows really well,” said Lawrence Heaney, Curator of Mammals at the Field Museum of Natural History in Chicago.

Minks are “inconspicuous … and for the most part pretty innocuous,” Dr. Heaney said, adding, “They don’t really bother things much.”

Semi-aquatic, minks live near freshwater streams and ponds, where they find their feed on small mammals such as voles that live near the water’s edge as well as little crustaceans like crayfish. Birds, reptiles, amphibians, insects, ?shes, muskrats, mice and cottontails are also part of their diet.

A mink may live under a brush pile or take over the house or bank burrow of a muskrat, according to the Illinois Department of Natural Resources. Anyone who wants to look for a mink should look near the water for footprints and be aware of odors. Their latrine “would have this very strong, almost skunky sort of odor,” Dr. Heaney said.

Not seen – or maybe not recognized – as often as their relatives, the otter, the weasel and the ferret, minks are prized for their furs. “They spend so much time in water that they have very, very dense, soft fur that repels water really well,” Dr. Heaney said. “You know, when you when you clean it up, it’s really gorgeous.”

As do many mammals, minks mark their territory with a “very, very strong musky material produced by the oil glands,” Dr. Heaney said. Asked whether people eat minks, Dr. Heaney said the musk likely permeates the meat as well “so you really wouldn’t want to eat it.”

The four-month mating seasons runs from winter to spring – January through April – with a litter of three to six babies, called kits, born before the summer. The gestation period, according to the Illinois Department of Natural Resources, “is variable and determined by when the fertilized eggs implant and begin development in the uterus.”

Born helpless but able to live on their own after about two months, the kits may remain near their birthplace but the young eventually leave the mother and look for a new place to live, said Dr. Heaney. “And when they do that, sometimes they’ll go a long way away from water. And so people will occasionally see them in other places, but for the most part, they’re going to be near a creek or a river or a pond or lake.”

Asked what minks contribute to the environment, Dr. Heaney said, “I’d have a hard time saying this particular species is critically important in some ways. They’re part of the community of organisms that live around us. And, yes, if we were to remove them, I’m sure that there would be some effects that would probably be increases in some of the things that they eat. Maybe that would cause some trouble.

But for the most part, they just belong here. It’s great.”