Invertebrates
Tongue Worm
Pentastomida · also called tongue worms, pentastomids
A tongue worm looks like a simple segmented worm and lives somewhere genuinely unpleasant to imagine, inside the lungs or nasal passages of a snake, lizard, or crocodilian, gripping internal tissue with small hooks while feeding on blood and tissue fluid. Its real identity is stranger still: genetic studies place it as a highly modified crustacean, a far closer relative of crabs and shrimp than of any true worm.
Overview
Tongue worms, subclass Pentastomida, are internal parasites found wherever suitable reptile hosts occur across tropical and subtropical regions. Adults typically live within a host’s respiratory system, most often a snake, lizard, or crocodilian, feeding on blood and tissue fluid.
A worm in name only
Despite the name and wormlike body shape, tongue worms are now understood to be highly modified crustaceans. Many species pass through an intermediate host before reaching their reptile host through the food chain, completing a life cycle spread across more than one animal.
Status
Least Concern — its population tied directly to reptile host abundance, remaining widespread wherever suitable hosts persist.
Tongue Worm: common questions
Is a tongue worm really more closely related to crabs than to earthworms?
Yes, despite its long, segmented, superficially wormlike body, genetic and detailed structural analysis has shown that tongue worms are highly modified crustaceans, placing them much closer, evolutionarily, to animals such as crabs, shrimp, and copepods than to true segmented worms like earthworms, making the tongue worm's actual evolutionary relationships considerably different from what its appearance alone would suggest.
Where inside an animal does a tongue worm actually live?
Adult tongue worms most commonly live within the respiratory system of their reptile host, typically in the lungs or nasal passages of snakes, lizards, or crocodilians, where they attach to internal tissue using small hooks near the mouth and feed on the host's blood and tissue fluids for an extended period.
How does a tongue worm get from one host to another?
Many tongue worm species rely on an intermediate host, often a smaller animal that the primary reptile host later eats as part of its normal diet, and the parasite is transmitted from the intermediate host to the reptile host through this predator-prey feeding relationship, allowing the tongue worm to complete different stages of its life cycle across more than one host animal.
Can tongue worms infect humans?
While tongue worms primarily parasitise reptiles, certain tongue worm species have been documented in rare cases infecting humans, generally through accidental ingestion of contaminated food or water containing infective larval stages, though such human infections are considered uncommon and are not the typical or intended life cycle pathway for most tongue worm species, which are adapted specifically to reptile hosts.