--- title: "Hydra (Hydra vulgaris) | AnimalTracks.wiki" description: "A small freshwater polyp whose death rate in lab studies stayed flat as it got older." image: "https://animaltracks.wiki/images/animals/hydra-1.webp" published: "2026-10-11" updated: "2026-10-11" --- # Hydra (*Hydra vulgaris*) > **Status**: Checked against 9 sources, listed under Sources below. > **Tagline**: A small freshwater polyp whose death rate in lab studies stayed flat as it got older. > **Soundtrack Vibe**: Glacial Ambient & Drone Soundscapes // GAS, "Pop 4" > **Soundtrack Links**: [Spotify](https://open.spotify.com/track/6tjzp1mCVaTeK5ZFAye3Ou) > **Vibe Match**: A hydra replaces all of its cells within four weeks, and in the lab its death rate stayed flat as it aged. Pop 4 is built the same way: one loop keeps cycling while the sounds layered over it keep changing. ## Biological Superpowers & Stats - **Taxonomy**: *Hydra vulgaris* - **Danger Level**: Low - **Conservation Status**: Not Evaluated ([IUCN Red List](https://www.iucnredlist.org/)) - **Superpower**: Replaces all of its cells within four weeks - **Habitat**: Fresh water, with Hydra strains collected from around the world - **Diet**: Small prey such as copepods and other zooplankton - **Tags**: cnidarian, freshwater, regeneration, predator ## Natural History & Behavior ## Tiny tube, loaded tentacles Hydra is a freshwater polyp, an animal with a tube-shaped body. It measures between 2 and 10 mm in length, though the body can reach up to 30 mm. Its head is ringed by tentacles. It belongs to the phylum Cnidaria, the group that also holds jellyfish, sea anemones and corals. Researchers have collected Hydra strains from around the world. The tentacles are packed with cnidocytes, cells that hold stinging parts and are rich in neurotoxic substances that paralyse prey. Hydra feeds on small animals such as copepods and other zooplankton, which are tiny creatures that drift in water. Once the tentacles have caught a meal, it is moved to the hypostome, the mouth opening. ## A death rate that stays flat For a long time, scientists thought that every animal that breeds repeatedly would see its death rate rise and its fertility fall with age after maturity. A 2015 study put that to the test on 2,256 Hydra from two closely related species. Spread across 12 groups in two labs, they had extremely low, constant rates of mortality. > **Forever young, in a dish** > In a lab in Rostock, Germany, researchers cared for about 1,800 polyps over almost ten years, each in its own small glass dish at a constant 18 degrees Celsius, fed three times a week. Their yearly chance of dying stayed at a low 0.6 percent. For humans, it reaches levels as high as 50 percent at advanced ages. The lab is a kind place, though. In the wild, Hydra's average life span is counted in weeks rather than years, because of high extrinsic mortality, which is the death rate from outside causes. ## Rebuilt every four weeks The researchers say features such as a high proportion of stem cells and rapid cell turnover may make that flat death rate possible. Its stem cells can develop into any part of the body. Hydra replaces all of its cells within four weeks, and it regularly expels cells that mutations have changed. It can completely replace body parts that are damaged or lost, and it can fully regenerate if its body is almost completely destroyed. It reproduces mostly without a partner, by budding, which makes genetically identical clones. Warmth boosts budding. By the end of one lab test, an average of 45 polyps were budding at 25 degrees Celsius, against 4 at 15 degrees. ## Frequently Asked Questions ### Does a hydra have a nervous system? Yes. It was long described as a simple nerve net. In 2017, researchers used calcium imaging to record the activity of essentially all of its neurons and found a series of networks that do not overlap, each tied to a specific behavior. One network is active when the body contracts lengthwise, another when it stretches in response to light. *(Source: [Dupre & Yuste 2017]())* ### How does a hydra make more hydras? It can reproduce sexually, but it also buds. Under favorable conditions, a bud forms in the lower section of the body, passes through 10 stages of growth and tentacle formation, then detaches as a new polyp. *(Source: [Destry, Cochran & Macias-Muñoz 2025]())* ### How did scientists test whether hydra age? One test, published in 1998, followed three groups of hydra for four years and tracked deaths and reproduction. Death rates stayed extremely low and reproduction showed no apparent sign of falling. *(Source: [Martı́nez 1998]())* ## Sources 1. [Auclair et al. (2024). Ecotoxicity of a Representative Urban Mixture of Rare Earth Elements to Hydra vulgaris. Toxics.]() 2. [Klymenko & Lutz (2026). From Hydra to Humans: Head Activator in Neurogenesis and Neurorepair. Cells.]() 3. [Destry, Cochran & Macias-Muñoz (2025). The effect of temperature on asexual reproduction in Hydra vulgaris. microPublication Biology.]() 4. [Schaible et al. (2015). Constant mortality and fertility over age in Hydra. Proceedings of the National Academy of Sciences.]() 5. [Forever young. Max Planck Institute for Demographic Research, press release.]() 6. [Martı́nez (1998). Mortality Patterns Suggest Lack of Senescence in Hydra. Experimental Gerontology.]() 7. [Sahm et al. (2024). Hydra has mammal-like mutation rates facilitating fast adaptation despite its nonaging phenotype. Genome Research.]() 8. [Schenkelaars et al. (2020). The polymorphism of Hydra microsatellite sequences provides strain-specific signatures. PLOS ONE.]() 9. [Dupre & Yuste (2017). Non-overlapping Neural Networks in Hydra vulgaris. Current Biology.]() *Published October 11, 2026. 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