Size: 1 mm
Det. H.C. Proctor 2010: "During sperm transfer the female, who is completely globular in shape, is glued to the extension of the male's body by glandular secretions. Adult and nymphal Arrenurus spp. feed mainly on ostracods, and larvae are parasites on either mosquitoes or odonates."
Image at BugGuide.net
iNaturalist observation