Riccardoella limacum or the slug mite is a member of the Acari (mite)[1] family which is parasitic on slugs and snails. Slug mites are very small (less than 0.5 mm in length), white, and can be seen to move very rapidly over the surface of their host, particularly under the shell rim and near the pulmonary aperture. While once thought to be benign mucophages, more recent studies have shown that they actually subsist on the host's blood,[2][3] and may bore into the host's body to feed.


Mite infection among gastropod populations varies greatly. Dense gastropod population favors infection; isolated populations may remain uninfected. Older and larger gastropods are more likely to show infection. Mites have been observed to move from host to host when hosts mate, and when gastropods congregate in moist soil and under rocks during the day. It has been shown that mites move preferentially towards fresh mucus when they travel along mucus, enabling them to follow mucus trails to new hosts. Once infected, individual gastropods take longer to mature and show reduced mating, activity, and feeding. Infected slugs and snails lay fewer eggs than uninfected individuals. Infected gastropods also show decreased winter survival rates.

At least 31 species of mollusks are exploited. Common hosts include the following:

  • Deroceras agreste
  • Arianta arbustorum
  • Arion ater
  • Arion hortensis
  • Cornu aspersum
  • Helix pomatia
  • Limax maximus
  • Milax budapestensis
  • Milax gagates
  • Milax sowerbyi


The slug mite was first identified in 1710 by entomologist René Antoine Ferchault de Réaumur. Three species were subsequently named, though they were synonymized as Riccardoella limacum in 1946.

Life cycleEdit