Tiger flatworm
Girardia tigrina
The tiger flatworm is a freshwater planarian native to North America that has spread globally as a non-native species in various aquatic ecosystems. It is characterized by a brownish base color with irregular light spots or stripes, giving it a tiger-like appearance. The species is well-known for its extreme regenerative capabilities and its adaptability to different types of water bodies.
Details
Identification
Triangular head with two distinct auricles, two light eyespots, characteristic dark mottling on a lighter background.
Social behavior
Mostly solitary, but forms dense aggregations when food supply is high.
Diet
Carnivorous and scavenger; feeds on small crustaceans, insect larvae, snails, and oligochaetes.
Hunting strategy
Uses chemoreceptors to track prey and entangles it using sticky mucus.
Spawning substrate
Undersides of stones, wood, or aquatic plants.
Overwintering
Overwinters in the sediment or as egg capsules; tolerant of low temperatures.
Ecology
Ecological role
Important benthic predator; can displace native planarian species through competition and predation.
Natural predators
Fish, predatory insect larvae (e.g., dragonfly larvae), and water beetles.
Competitor species
Native flatworms such as Polycelis nigra or Schmidtea polychroa.
Ecosystem service
Contributes to the decomposition of organic matter (carrion) in water bodies.
Threats
No significant threats; benefits from anthropogenic water body alterations.
Scientific profile
Profile
Distinguishing features
The most important feature is the distinctly triangular head with two short, laterally projecting auricles (sensory lobes). Unlike many native Dugesia species, the body is mottled rather than monochrome. The pharynx in this species is pigmented. The eyes are positioned relatively close together in the anterior third of the head.
Diet
Small invertebrates such as oligochaetes (worms), isopods, chironomids (midge larvae), small snails, and amphipods (gammarids).
Reproduction
Both sexual (as a hermaphrodite via egg cocoons) and asexual by transverse fission followed by regeneration. In European invasion areas, asexual reproduction dominates almost exclusively.
Role in food web
Secondary consumer; as an invasive species, it can displace native planarians (e.g., Polycelis species) through predation and food competition.
Protection & threats
Status not on standard scale
Main threats
None known; the species is a successful neozoon in Europe and benefits from the warming of water bodies.
Conservation measures
No conservation measures required; monitoring of its spread to assess the impact on native biodiversity.