A railroad worm is a larva or larviform female adult of a beetle of the genus Phrixothrix in the family Phengodidae, characterized by the possession of two different colors of bioluminescence.
It has the appearance of a caterpillar.
The "railroad worm" name arises because these glowing spots along the body resemble the windows of train cars internally illuminated in the night. The light emissions are believed to be a warning signal to nocturnal predators of their unpalatability.
Here, it is representing a portal that transits to another universe.