Family common name: common sawflies
Genus: Heptamelus Haliday, 1855
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).
Heptamelus is monotypic in North America (Taeger et al. 2010). Heptamelus dahlbomi is small, about 5 mm in length, with a black body and light yellow-colored legs. This species is a fern-feeding sawfly (Smith 1969e).
Heptamelus can be confused with similar species in the subfamily Selandriinae. It can be distinguished from most other genera by the fewer number of antennal segments and combination of wing venation characteristics (Smith 1969e, Goulet 1992).
North American hosts for H. dahlbomi are not known. Hosts in Europe include ferns Athyrium filix-femina (common lady fern), Athyrium distentifolium (alpine lady fern), Blechnum (hard fern), and Polypodium (Goulet 1992, Liston et al. 2018).
Female H. dahlbomi deposit eggs into the lower part of the frond where it meets the petiole. Larvae are grayish-white and feed on the petiole, causing damage to the leaf growth above (Vikberg and Liston 2009).
Heptamelus dahlbomi was likely introduced to North America, but it is not clear from where or how (Liston et al. 2018). No males in native or introduced range are recorded, suggesting this species is parthenogenetic (Vikberg and Liston 2009).
North America: Heptamelus dahlbomi occurs in British Columbia, Maryland, and Virginia (Vikberg and Liston 2009).
Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Heptamelus and the Smithsonian National Museum of Natural History Entomology Collection (USNM)
Details about data used for maps can be found here.