Folsomia brevicauda is a common species of bogs and other acidic habitats with a pronounced western bias to its distribution. It is greyish brown with 2+2 ocelli (Fig. 1) and reaches a maximum length of 0.7 mm. The body setae are short; the ratio of the length of the longest setae at the tip of the abdomen/length of mucro is between 2.0 to 3.0. The manubrium has 1+1 apical ventral (anterior) setae. The short and stout dens has only 3 ventral (anterior) setae and 3 dorsal (posterior) setae (Fig. 2). The PAO is quite narrow and is about the same length as the width of ant1. A unique feature is the presence of 4 (sometimes 3) setae on the tenaculum (all other UK/Eire Folsomia have only one seta on the tenaculum).
Blackith (1974) rather implausibly, considered Folsomia brevicauda to be the most abundant arthropod in Ireland. This impression doubtless came about from the high densities that this species can be found at in its preferred acid bogs; virtually every soil core that Peter Shaw extracted from the forested moors of Spadeadam (Borders, near Hexham) was numerically dominated by this species.