Mexican black kingsnake hunger strike

[Bogertophis]

As Homebody said, I'd weigh him every other week to make sure he's not losing more than 10% of his body weight. I can't remember the MBKs I used to have ever refusing food for ANY reason, but it still could be the spring-mating thing with yours, although it's not as common for immature snakes like yours. What size (approx. length & weight) is yours? I'm very much a colubrid keeper, btw.

Have you listened closely to his breathing? For signs of an RI? Respiratory infections can put off a snake's appetite, as can other illnesses.

Have his stools looked normal? Getting them tested by a qualified herp vet is another way to go- as parasites can also affect appetite. https://members.arav.org/search/custom.asp?id=3661

Was he fed live prey ever? Live prey can pass along intestinal parasites to the snake consuming them.

Probably a silly question, but how warm is he being kept? Have you checked to make sure his UTH (heat) is still operating & at the right temperature??? Or whatever you're using for heat? Details about his home would help- for example, if his enclosure is near the floor, it's much cooler there than if kept higher up- so maybe his heat is not adequate. Snakes that feel too cool anticipate winter & fast intentionally so they don't die if they get caught with undigested food in their gut that they cannot digest because it's too cool. And if you using only an overhead heating method, have you double checked the temperatures on the floor of his home? All this may matter- snakes are stuck where they are in captivity- they can't go searching for the right temperatures- we have to provide them, & if we fail to do so, it shows up in their lack of appetite.

Another thing that can affect a snake's appetite is excessive handling. Also, if your house/room is on the cool side because it's winter, & you have him out of his warmer home for a significant amount of time, that alone may be enough to put him off food. But also there's the stress aspect of handling, regardless of temperatures- & not everyone means quite the same thing by "handling" either. For best results, if a snake isn't eating, it should not be handled until it is- in case the food refusal is actually due to stress.