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) considered Folsomia brevicauda to be the most abundant arthropod in Ireland. If this is the case then it is very under-recorded!

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Fig. 1 (above): Post-antennal organ (PAO) and ocelli of Folsomia brevicauda collected from Glen Coe in Scotland in September 1966 by T. Clay.

Fig. 2 (left): Furca of Folsomia brevicauda collected from Glen Coe in Scotland in September 1966 by T. Clay. ma, manubrium; d, dens (bent under cover slip on one side); *, 1+1 apical ventral (anterior) setae on manubrium.