Just hop to cultist sites until you find one with mothman at it. They are the head icon with the horns on it on the map.

If you have done the BoS Steel Reign etc quests, you can find one at Transmission Station 1AT-UO3 (south of Tyler County Fairgrounds).

Enclave Research Facility, always has one.

the medical facility in watoga i recall

edit: i was wrong

https://fallout.fandom.com/wiki/Queen_of_the_Hunt
gives you a chance to come across the mothman
what you should not do is kill a non-mothman (it'll end the spawns)
FT to each spot (hop to aother world if no mothman on the 3 locations) until it spawns

The Moth Man actually has multiple locations he can spawn at, but only with a 2.5% chance at each location and only at night. I'd personally recommend doing the Queen of the Hunt Daily quest when it is night time in game as that can spawn the moth man as the cryptid you have to kill for completion.

Originally posted by Eccentric Recluse:

The Moth Man actually has multiple locations he can spawn at, but only with a 2.5% chance at each location and only at night. I'd personally recommend doing the Queen of the Hunt Daily quest when it is night time in game as that can spawn the moth man as the cryptid you have to kill for completion.

you sure it has to be night?

Random encounters and certain spawns only at night.
I re-rolled that @#$%.

Originally posted by BizarreMan:

If you have done the BoS Steel Reign etc quests, you can find one at Transmission Station 1AT-UO3 (south of Tyler County Fairgrounds).

Originally posted by Ildun:

Enclave Research Facility, always has one.

What these two said.