railroad worm

noun
  1. the larva of a fruit fly, Rhagoletis pomonella, that burrows through apples, forming tunnels that sometimes appear on the skin as faint depressions or darkened trails: a serious pest of apples in colder regions of North America.

Origin of railroad worm

First recorded in 1905–10
Also called apple maggot.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018