Sminthurides malmgreni is a very common and widespread species (more common and widespread than Sminthurides aquaticus). The body is yellow in colour with longitudinal bands of blue pigment (Fig. 1), although Paul Ardon has recently found the black form Sminthurides malmgreni ssp nigrescens on the surface of peaty pools on Dersingham bog, Norfolk. Males reach 0.3 mm in length whereas females grow to 0.6 mm.
In Sminthurides species, the male antenna is modified to grasp the female during mating and the long spine on the second antennal segment (ant2) is curved (Fig. 2). Females do not possess sub-anal appendages (SAA). In Sminthurides malmgreni, the fourth antennal segment in the female is not divided into clear subsegments (Fig. 3). The mucro is about one third as broad as long and the ventral lamella is striated (Fig. 4). A tibiotarsal organ (tt organ) is present on the third leg and the long seta bears a lamella (Fig. 5). The empodium of the foot has a long filament that reaches well beyond the tip of the claw (Figs. 6, 7).
Sminthurides malmgreni is most frequently found on the surface of standing water; its mucro shape is thought to help it jump off the water surface.