Coastal Silver-stiletto vs common hydra

Acrosathe annulata compared with Hydra vulgaris

Key Differences

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

Taxonomic Classification

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

Evolutionary Relationship

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

Conservation Status

Coastal Silver-stiletto

LC — Least Concern

common hydra

NE — Not Evaluated

Physical Characteristics

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

Habitat & Geographic Range

Coastal Silver-stiletto

Habitat

Typically found in virtually all terrestrial and freshwater habitats.

Range

Distributed across Belgium, Denmark, Norway, and Sweden.

common hydra

Habitat

Native to Europe, inhabiting ecosystems characteristic of the region.

Range

Distributed across Denmark, Norway, and Sweden.

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.

common hydra

<em>Hydra vulgaris</em>, commonly known as the common hydra, is a small freshwater cnidarian in the family Hydridae. Its conservation status has not been formally evaluated by the IUCN. The species is recorded from Denmark, Norway, and Sweden, with its native range understood to encompass Europe broadly. It typically inhabits slow-moving or still freshwater bodies such as ponds, lakes, and streams, where it attaches to aquatic vegetation or submerged substrates. The common hydra is notable for its remarkable regenerative capabilities and has been the subject of substantial biological research. Diet information for this species is not available in current records. Biological traits of this species remain poorly documented in the scientific literature.

Shared Countries

Both species can be found in 3 countries:

🇩🇰 Denmark 🇳🇴 Norway 🇸🇪 Sweden