First, protect your other reptiles
A king snake escape carries a risk no other snake on this list poses: kingsnakes are snake-eaters, and a loose one hunts by scent, which means your other snakes' enclosures are the most attractive destinations in the house. Before you search a single baseboard, check every other reptile enclosure in the home, confirm its lid is secured, and if any tank cannot be made escape-proof in a minute, move its occupant in a latched tub into a closed room. Only then start hunting the hunter.
Note the exit route while you are at it. King snakes are powerful for their size and defeat lids by sustained pushing at corners, so look for the corner or vent that flexed.
Where an active hunter holes up
Unlike a ball python, who picks one warm gap and stays, a king snake covers ground: along baseboards, up into closets, behind and inside appliances, and through any wall gap near plumbing. Search at night with a flashlight, working a room at a time with doors closed, and weight your attention toward warm equipment backs — refrigerators, washers, entertainment units — and toward the room that houses your other reptiles, where scent alone may have drawn him into a nearby crevice.
Check the cool spots too. A king snake who has found food or simply traveled far may settle somewhere merely dark and undisturbed: inside storage boxes, under the bottom drawer of a dresser, in the folds of stored bedding. Move items out of the room as you clear them so the searched ground stays searched.
Traps for a snake that is out hunting
A hunting snake is a moving snake, and movement can be mapped. Lay thin flour lines across doorways and along the baseboards of suspect rooms before dark; by morning, a trail through the flour tells you his corridor. Place his hide — or any snug box with a snake-sized entrance — on the floor against the wall on that corridor, with a water dish beside it, and let the hide do the waiting. Crinkly plastic bags taped along the wall line add ears to the trap: a king snake crossing them at night announces the room he is in.
Repeat the layout for several nights and resist declaring the house clear early. A king snake who has eaten — or found one warm, perfect gap — can stay invisible for days between patrols.
A calm capture and a stronger lid
When you corner him, expect the king snake repertoire: flattening, tail rattling against dry surfaces, musk, and possibly a bite that is more startling than harmful. Move slowly, let him smell your hand, and lift him mid-body into a ventilated, latched tub rather than seizing him behind the head, which escalates the struggle. Wash up afterward; musk lingers cheerfully on fabric.
Then rebuild against his actual strength: a lid that locks, not one that merely rests; vents he cannot flex; corners reinforced. And if the flour lines and hides come up empty for the better part of a week, consider the building itself — pipe chases and duct gaps can carry a slim snake astonishingly far — and warn your neighbors. KinsLe's Lost Pet Alert System alerts nearby pet lovers for free, so if your king snake surfaces in a neighbor's garage, that neighbor can message you directly through his profile.