Thursday night at eight, an Ijams Park naturalist takes a group out onto the trails to look up. The program is called Ijams After Dark: All About Bats, it runs an hour and a half, and the premise is that the animals doing the most work over South Knoxville after sunset are the ones almost nobody has ever knowingly looked at.

★The bat house is the real headliner

Out on the property there is a structure ten feet by twelve, fitted inside with vertical plywood slats and a walkway for the people who monitor it. It was built to hold up to a hundred thousand Brazilian free-tailed bats while they roost, rest and raise their young. It stands on ground that held industrial lime kilns until the early 1970s, which is the whole story of this park in one sentence: a place that was used hard, then handed back.

★What the night actually involves

You learn to tell species apart as they pass overhead, and you stop at blacklight stations, where a violet lamp on a patch of forest turns up an entire layer of insects and lichens that simply is not visible at noon. Expect up to a mile and a half of walking over rocks, roots and gravel, with stops along the way — real shoes, not sandals. Fifteen dollars, ages ten and up, and registration is required in advance.

★One rule, stated plainly

Never touch a bat. The park is blunt about it and so are we; these are protected wild animals and the reason for the rule is rabies. Watch from behind the fence at the observation area, keep your distance, and let the naturalist do the pointing.