Fossorial Silkworm

Underground you can find strange solid animals hanging on the ceiling. Upon further inspection you find they love glowberries and after eating some will create a large rope that reaches all the way down to the ground. You can grab onto this rope and climb it all the way until you've escaped. Feeding it again will make it so happy that it will retract its rope and crawl up into your hand. Now you can use this lovely creature to traverse the caves easier as well as give yourself new friends to play with. breaking its string might drop a salvageable piece of string, but you'd need to feed it again to replenish its string.