Say, you don't want to get lost in a tunnel, so you set a rope that leads back to the entrance (or likewise follow another rope set by another person).
I searched for guide rope and guiding rope but I'm not sure whether it's the right word:
Example sentence (in case it is needed):
The male can find a female miles away, as if they were following a [...]
If you want to be mythological, the term is Ariadne's Thread. When Theseus entered the Labyrinth to kill the minotaur, he unwound a ball of thread given to him by Ariadne. Following the thread allowed him to escape the maze.
breadcrumbs. See breadcrumb trail.
Actually, guide rope (or guiderope) makes the most sense and it is easy to understand. It is also used in various contexts for a rope that guides you back.
In caving:
He lost his light but was still able to pull himself out as he hadn't let go of his guide rope.
"Caving in Ontario; Exploring Buried Karst" By Michael Gordon
In freediving:
Free immersion apnea is a discipline in which the athlete uses the vertical guiderope to pull him or herself down to depth and back to the surface. It is known for its ease compared with the Constant Weight disciplines, while the athlete is still not allowed to release weights (AIDA). [Wikipedia]
In firefighting:
Before entering the building, secure one end of the guide rope to a substantial object on the outside. The remaining rope is then carried by one member, designated as the "anchor".
You should deploy a guide rope in any building where disorientation and depletion of air supply are possible. Large-area office building, hospitals and schools are excellent candidates for the guide rope, as are tunnels, ships and subways.
"Fire Officer's Handbook of Tactics" By John Norman
Note: Guide rope has another meaning also but context is everything.
Lifeline is another that could sensibly be used here, though it also has other meanings.
This also has an echo in the thread that in some mythologies connect a body to the soul or spirit, allowing it to find its way back.
Also, you can just refer to it as a "string" or "twine" or "spool" or if you want to be archaic, a "clew" (which has a nice homophone in "clue", which such a trail is!).
[edit: in the example sentence, "wire" would work too, at least for flying creatures like moths, bats: "The male can find a female miles away, as if they were on a wire". Also consider "...as if guided by a beacon", "...as if following a map", etc]
