brown hydra vs Coastal Silver-stiletto

Hydra oligactis compared with Acrosathe annulata

Key Differences

• brown hydra is Not Evaluated while Coastal Silver-stiletto is Least Concern.

Taxonomic Classification

Rank	brown hydra	Coastal Silver-stiletto
Kingdom same	Animalia (Animals)	Animalia (Animals)
Phylum	Cnidaria (Cnidarians)	Arthropoda (Arthropods)
Class	Hydrozoa (Hydrozoa)	Insecta (Insects)
Order	Anthoathecata (Anthoathecata)	Diptera (Diptera)
Family	Hydridae	Therevidae
Genus	Hydra	Acrosathe
Species	Hydra oligactis	Acrosathe annulata

Evolutionary Relationship

brown hydra and Coastal Silver-stiletto share a common ancestor at the Kingdom level: Animalia. (Animals)

Conservation Status

brown hydra

NE — Not Evaluated

Coastal Silver-stiletto

LC — Least Concern

Physical Characteristics

Attribute	brown hydra	Coastal Silver-stiletto
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

brown hydra

Habitat

Native to Europe, inhabiting ecosystems characteristic of the region.

Range

Distributed across Denmark, Norway, and Sweden.

Coastal Silver-stiletto

Habitat

Typically found in virtually all terrestrial and freshwater habitats.

Range

Distributed across Belgium, Denmark, Norway, and Sweden.

brown hydra

The Brown Hydra (Hydra oligactis) is a species in the genus Hydra. Native to Europe, inhabiting ecosystems characteristic of the region. Distributed across Denmark, Norway, and Sweden. As a member of the Hydra genus, this species contributes to biodiversity in its native range.

Coastal Silver-stiletto

Coastal silver stiletto (Acrosathe annulata) is a slender robber fly in the family Therevidae, native to northwestern Europe, including the United Kingdom, France, the Netherlands, Belgium, and Scandinavia. Adults are found on coastal sand dunes and sandy heathland, where they perch on bare sand to ambush small flying insects. Stiletto flies in the family Therevidae are characterised by a slender body, long pointed abdomen, and predatory habits; adults prey on a variety of small dipterans and other flying insects during warm, sunny periods. Larvae develop in sandy soil, where they are also predatory, feeding on other invertebrate larvae. Acrosathe annulata is a habitat specialist restricted to open, sandy coastal habitats with sparse vegetation—environments that have declined substantially across northwestern Europe due to dune stabilisation, recreational disturbance, and the cessation of traditional dune management. The IUCN lists it as Least Concern, though regional conservation bodies in the United Kingdom have flagged population declines. It is considered an indicator of high-quality coastal sand dune habitats and is monitored through national invertebrate surveys.

Shared Countries

Both species can be found in 3 countries:

🇩🇰 Denmark 🇳🇴 Norway 🇸🇪 Sweden