Canadian Journal of Arthropod Identification

Sciomyzidae of northeastern North America

CJAI 35 -- March 20, 2019

Sarah Schorno, Stephen A. Marshall, William L. Murphy, and Matthew J. Muzzatti

| Abstract | Introduction | Materials & Methods | Checklist | Similar Families | Glossary | Key to Genera | Acknowledgments | References | PDF | Cite |



The family Sciomyzidae (commonly known as snail-killing flies or marsh flies) is one of the best known dipteran families, in part because of the unique feeding behaviour of the larvae. Sciomyzidae is the only dipteran family with larvae almost exclusively obligate killers of molluscs (Murphy et al. 2012) and members of this family are the most frequently studied of all natural enemies of terrestrial gastropods (Barker et al., 2004). The feeding behaviour of larvae is diverse, ranging from saprophagous to predaceous to parasitoid, with many species having mixed or facultative behaviours (Knutson and Vala, 2011). Sciomyzidae have potential to serve as successful biological control agents of potentially harmful or destructive gastropods (Ehler and Miller, 1978).
Adult Sciomyzidae are slender to robust flies, ranging in length from 1.7 mm (Colobaea americana) to 13.0 mm (Salticella stuckenbergi). They range in colour from shiny black (Pteromicra spp.), to dull gray or brown (many Pherbellia spp.), to subshiny brown (Tetanocera spp.) or yellowish (some Pherbellia spp.) (Knutson and Vala, 2011). Characteristically, adults fly quite low, slowly and for short distances, while their resting posture is often described as frog-like, with the head usually directed downward (Knutson and Vala, 2011). Sciomyzidae are readily distinguished from most other acalyptrate flies by a combination of external features including: antenna often porrect with elongated pedicel, oral vibrissae absent, postocellar setae parallel to slightly diverging, no more than two fronto-orbital setae, costa entire, subcosta complete, one or more tibiae with preapical setae, and clypeus inconspicuous (Barker et al., 2004; Knutson and Vala, 2011). Many other families of acalyptrate are sometimes confused with species of Sciomyzidae, especially Dryomyzidae, Heleomyzidae, and Lauxaniidae.
The Holarctic region has the largest diversity of marsh flies, with 63 genera and more than half of the world’s fauna of 543 species (Murphy et al., 2018). Twenty-one genera and 98 species occur in eastern Canada and the adjacent U.S. states. All belong to the subfamily Sciomyzinae and can be readily segregated into two tribes, Sciomyzini and Tetanocerini, on the basis of presence or absence, respectively, of a well-developed proepisternal seta.
Here, we provide a full-colour photographic key to the genera and species of Sciomyzidae of eastern Canada, including species not yet known from Canada but known from adjacent U.S. states, and possibly occurring but so far unrecorded north of the border between the U.S.A. and Canada.