Fauna
Invertebrate

Brown Hydra

Hydra oligactis

Also known as Stalked Hydra

Brown hydras are solitary freshwater polyps renowned for their remarkable regenerative abilities and distinctly slender, stalked body columns. Anchored to submerged vegetation or debris with a sticky basal disc, they extend ultra-fine tentacles equipped with venomous nematocysts to ensnare swimming micro-crustaceans. As water temperatures cool toward autumn, they shift from rapid asexual budding to sexual reproduction, producing hardy resting embryos that survive the winter.

FreshwaterAquaticCarnivorous
Brown Hydra reference1 / 5
(c) Igor Shelpiakov, some rights reserved (CC BY) · cc-by
—observations
—countries
—peak records
Not EvaluatedConservation statusIUCN Red List categoriesLCNTVUENCREWEXNot Evaluated — not placed on the risk ladderRed List categories, explained →
Key facts
Diet & preyDaphnia water fleas, Cyclopoid copepods, Ostracods
Predators
  • Line microstomum flatworm
  • Great pond snail
  • Juvenile freshwater fish
ThreatsChemical pollution, agricultural runoff, severe eutrophication, and heavy sedimentation
HabitatsPonds, calm lake margins, slow-moving streams, and permanent ditches
Life spanPotentially indefinite due to continuous cellular renewal; wild polyps live several months
Classification
  1. OrderAnthoathecata
  2. FamilyHydridae
  3. GenusHydra
  4. SpeciesHydra oligactis
Range & activity
Range data is not available yet.
Safe observation
Interaction riskLow
  1. Low
  2. Moderate
  3. High
  4. Very high
Why interaction risk is low
Harmless to humans; microscopic stinging cells cannot penetrate human skin.
Responsible observation
  • Jar Observation: Scoop submerged pond weeds into a clean glass jar and let it sit still for twenty minutes to watch polyps stretch.
  • Magnification: Use a 10x hand lens against direct sunlight to view budding clones and extended tentacle nets.
  • Gentle Handling: Polyps immediately contract into tiny brownish balls when jostled, so keep collection containers steady.
Related species
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