Bark Lice

• It reproduces by parthenogenesis and no males are known: each female produces clones of herself, which lets it colonise a whole store from a single individual.
• Its presence indicates high humidity: it disappears if the space is ventilated and dried out, because it depends on fungi that need that moisture.
• It is a serious pest in archives, libraries and natural history collections, and in the food industry too, where it contaminates stored grain.
• For decades only females were known: it reproduces by parthenogenesis and populations are almost entirely female. The first male was not found until 2002, in Hawaii.
• Every parthenogenetic line analysed carries an endosymbiotic bacterium of the genus Rickettsia, absent from those that do reproduce sexually, which points to the bacterium causing the parthenogenesis.
• It is tiny — around a millimetre — and wingless, and goes unnoticed until the population explodes.
• It can cause a 9.7 % weight loss in cracked wheat grain over three months, and carries pathogenic micro-organisms and allergenic proteins.
• In 2019 it was identified as a predator of mosquito eggs in an FAO and IAEA laboratory.

Habitat & environment

Books, herbaria, grain stores and damp corners of houses

Sources consulted: Perlman et al.; Yang et al. (2015), Scientific Reports; Bai et al. (2025), Insects