The Geocoridae are easily distinguished from other hemipteran families by their very typical head shape. Some members of other families (e.g. Phlegyas spp.: Pachygronthidae) have a similar head shape, but only Geocoridae have large, reniform eyes reaching the lateral borders of the pronotum (Kóbor, 2020). Within this family, the genus Isthmocoris can be separated from the sole other North American genus, Geocoris, by the relative size of the rostrum segments. In the genus Geocoris, the second rostrum article is shorter than the third, whereas in Isthmocoris, its the opposite (Henry et al., 2015; Kóbor, 2020). Isthmocoris piceus (Fig. 2) is easily identified by the very characteristic shape of the head (strongly transverse), by the position of the ocelli (halfway between the middle of the vertex and the margin of the eyes), as well as the uniformly black coloration except for the vertex and the front of the head, which are bright red (Readio & Sweet, 1982; Scudder, 1985) (Fig. 3). It cannot be confused with other species in Quebec.

The Geocoridae family (previously included in the Lygaeidae) is small, with around 30 species in 2 genera in North America (Delapé and Henry 2024). In Quebec, only 4 species were known, all belonging to the genus Geocoris (Roch, 2020). The discovery of I. piceus increases the number of species in Quebec to 5, in 2 genera (Geocoris and Isthmocoris). Isthmocoris piceus is a widespread species in northeastern North America. It has been known from Ontario since 1985, following examination of a specimen captured in 1958 (Scudder, 1985), and from New York, Vermont, New Hampshire and Maine (Roch, 2020), as well as Massachusetts, Pennsylvania, Delaware, Illinois, Iowa, Kentucky, Wisconsin (BugGuide , 2024), Michigan and Indiana (INaturalist 2024). Its discovery in Quebec therefore comes as no great surprise, as its presence was already known in most of the neighboring territories. A specimen on the INaturalist site was also observed in the City of Ottawa, not far from the Ontario-Quebec border, indicating the species is potentially present in this area too.

Geocoridae are primarily predators of other arthropods, and are frequently studied for their impacts on various insect pests (e.g. Davis, 1981; Asa and Watson, 1982; Hutchison and Pitre, 1983; Eubanks and Denno, 1999; Olson et al., 2018). However, it is common to observe individuals feeding on plants, mainly for hydration purposes (Naranjo and Stimac, 1985).