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Wiktionary
railroad worm

n. 1 A larva or larviform female adult of a beetle of the genus (taxlink Phrixothrix genus noshow=1), characterized by two different colours of bioluminescence, red and green, like railroad signals. 2 The (vern: apple maggot) ((taxlink Rhagoletis pomonella species noshow=1))

WordNet
railroad worm

n. larvae bore into and feed on apples [syn: apple maggot, Rhagoletis pomonella]

Wikipedia
Railroad worm

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. The luminescent organs of their body can glow green, while those on their head can glow red; this is probably due to different luciferases in their bodies, as the reaction substrate, called luciferin, is the same. This is believed to be an adaptation to help confuse and frighten predators.

The term "railroad worm" is also sometimes applied to the apple maggot.