Coastal Silver-stiletto vs Floating Fern

Acrosathe annulata compared with Salvinia natans

Key Differences

Coastal Silver-stiletto is Least Concern while Floating Fern is Not Evaluated.

Taxonomic Classification

Rank	Coastal Silver-stiletto	Floating Fern
Kingdom	Animalia (Animals)	Plantae (Plants)
Phylum	Arthropoda (Arthropods)	Tracheophyta
Class	Insecta (Insects)	Polypodiopsida (Polypodiopsida)
Order	Diptera (Diptera)	Salviniales (Salviniales)
Family	Therevidae	Salviniaceae
Genus	Acrosathe	Salvinia
Species	Acrosathe annulata	Salvinia natans

Conservation Status

Coastal Silver-stiletto

LC — Least Concern

Floating Fern

NE — Not Evaluated

Physical Characteristics

Attribute	Coastal Silver-stiletto	Floating Fern
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.

Floating Fern

Habitat

Typically found in moist, shaded forest floors and tropical canopies.

Range

Widely distributed across Asia (4 countries), Europe (9 countries), North America (Honduras), and Oceania and the Pacific (Australia).

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.