So-called mythical creatures that were the plague of switchboard operators, controversial even unto the 1980's.
The story goes that there are insects that live in the nest where the cables rest that have a nasty bite. The Bell System repeatedly sent exterminators, entomologists, and other experts to find and eliminate these vermin; exterminators, entomologists, and others failed to find any insects whatsoever. However, switchboard operators continued to report insect bites and rashes on their hands, wrists, and arms up to the elbow, and sometimes respiratory and worse problems.
AT&T kept to its guns: there are no insects, therefore cable mites do not exist, thus consigning cable mites to cryptozoology.
The real culprit emerged with the discovery of dust mites. Fabric-wrapped cables invited dust, dust mites swarmed to consume the shed hairs and skin flakes of the operators, with the problem of dust mite feces, which in the human internal ecosystem, register as probable worm action, either internally or without. Skin, and sometimes other systems cry Red Alert! Worms Present!, and the body goes into overdrive trying to eject these nonexistent intruders.
A rare instance of a true urban legend, let's all keep 'truth' on a sliding basis.