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Marsh flies (Sciomyzidae)

Taxonomic group

Family: Sciomyzidae

Diagnostic features

The Sciomyzidae is another one of the less common families of true flies in our fresh waters. Their larvae are maggot-like, but the body is characterised by a very “bumpy” outline. There is no visible head, but there is a spiracular disc (breathing structure) at the end of the abdomen.

Typical habitats

Sciomyzid larvae are most likely to be found in slow flowing weedy streams, wetlands, ponds or lakes.


The sciomyzids are predators, preying primarily on molluscs, including sphaeriid bivalves and snails.

Indicator value

  • Hard bottom: 3
  • Soft bottom: 3

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

The ability of sciomyzids to tolerate slow-flowing, low-oxygen habitats allows them to live in waters of relatively poor quality. They therefore have low tolerance values of 3 for both hard and soft bottom sites.