Family common name: common sawflies
Genus: Strongylogaster Dahlbom, 1835
The Tenthredinidae are the most species-rich family and are found throughout the world, in all continents but Antarctica. They are known as the “common sawflies.” They can generally be recognized by a cylindrical body and long, segmented antennae. Otherwise, they come in a variety of colors, sizes, and forms (Goulet 1992).
Sawflies in the Selandriinae subfamily are relatively small and slender. The range of Selandriinae is worldwide; it occurs on all continents except Antarctica (Goulet 1992). It is the most common and diverse group of tenthredinids in tropical regions, particularly in Central America, South America, and Southeast Asia (Smith 1969e). Selandriinae contains the only known sawflies that feed on non-vascular plants, specifically ferns (Smith et al. 2013).The subfamily can be distinguished from other subfamilies by wing venation (Goulet 1992).
Strongylogaster are medium-sized, about 7 mm in length, and generally black, white, and orange. The genus is fern-feeding (Smith 1969e).
Strongylogaster can be confused with similar species in the subfamily Selandriinae or tribe Strongylogastrini. It can be distinguished from most other genera by the narrow median lobe of the mesoscutum, and from closely related Thrinax by the length of the pedicel and the setae on the median lobe of the mesoscutum (Smith 1969e, Goulet 1992).
In North America, Strongylogaster feeds on ferns, including Athyrium filix-femina (common lady fern), Osmunda, Pteridium aquilinum (eagle fern), Thelypteris (maiden fern), Gymnocarpium (oak fern), Woodsia (cliff fern), and Woodwardia (chain fern) (Smith 1969e, Goulet 1992).
Strongylogaster lineata larvae in Europe have defensive behaviors to limit predaceous ants that live on bracken fern to feed on the fern's extra-floral nectaries. When a larva is first cut by an attacking ant, it bleeds out hemolymph that is extremely sticky and distasteful to the ants. The larvae usually can heal after the initial attack, and the associated ants do not return (Heads and Lawton 1985).
World: This genus is known from North America, South America in Brazil, Ecuador, and Peru, Europe in the United Kingdom, and in Japan and China (Enderlein 1920, Smith 1969e, Smith and Naito 1995, Taeger et al. 2010).
North America: Strongylogaster is common in the eastern United States and Canada west through the Rocky Mountains into Idaho, Washington, and British Columbia (Smith 1969e). One species, S. panamensis, is known only from Panama (Dalla Torre 1894).
Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Strongylogaster
Details about data used for maps can be found here.