One of the ‘big five’ soldierflies (4 Stratiomys species plus Odontomyia ornata). This is the only one with an entirely black abdomen, though patches of pale hairs can create the impression of a pattern, and very small yellow spots are rarely present (nearly always present in southern European populations). Beware of S. singularior individuals with very small yellow spots – these have extensively dark hind tibiae and usually average larger. It also has a more hirsute appearance than other Stratiomys species
S. longicornis is almost entirely restricted to coastal areas, typically upper saltmarsh, tidal rivers and coastal grazing marsh where brackish pools, ditches and lagoons are present within (e.g. borrow dykes and old salt-winning areas). It will typically occur alongside S. singularior in such places but seems to specialise in more saline habitats. As a result of its more specialised needs, it is a much scarcer species with the bulk of the British population occurring within the Solent area, Sussex coastal marshes, Thames marshes and East Anglian coast.