neutral; feeds on nest debris

Name and classification

Acarus Linnaeus, 1758

Superorder Acariformes » Order Sarcoptiformes » Suborder Oribatida » Infraorder Desmonomata » Hyporder Astigmata » Family Acaridae » Genus Acarus

Type species
Acarus siro [var.] farinae Linnaeus, 1758 (=Acarus siro Linnaeus, 1758 as selected by Latreille, 1810)

Common synonyms
Tyroglyphus Latreille, 1796; Aleurobius Canestrini, 1888 (common historical synonyms)

Common names
flour mite (Acarus siro)


Adult: Bell-shaped structure present at entrance of canal of spermatheca in female (Fig. 11). Male with leg I enlarged and bearing a ventral apophysis (external projection from body wall) on femur (Fig. 14).

Other diagnostic characters

Phoretic deutonymph: Tarsal setae aa I, ba II present (Fig. 3). Seta ba I absent (Fig. 3). Solenidion ω3 of tarsus I situated in the middle of the tarsus, disassociated with ω1 (Fig. 3). Dorsal body surface with rounded depressions (Fig. 3). External conoidal setae ps2 of attachment organ lateral to median sucker (ad1+2) (Fig. 5). Sternal apodeme and anterior apodemes II not extending to level of coxal apodemes III. Setae of coxal fields I and III present, but very fine and short (Fig. 2). Empodial claws of pretarsi III-IV similar in form (Fig. 5). Solenidion ω2 of tarsus I absent, represented by vestigial alveolus (Fig. 3). Setae gT I-II and hT I-II distinctly barbed (Fig. 4). Genua III-IV subequal to tibiae III-IV (Fig. 5). Genu III without a short dorsal solenidion (σ) in addition to seta nG (Fig. 5).

Adult: Setae ve situated between the level of internal vertical setae (vi) and one-third the distance to scapular setae (se, si) (Fig. 10). Grandjean's organ complex, multifurcate (Figs. 10, 12). Genu I with solenidion σ' more than 3 times longer than σ'' (Fig. 13). Ventral apex of tarsus I with proral (p, q) setae thin (Fig. 12), and unguinal (u, v) setae short, stout spines (Figs. 12, 13).

Species identification

A dichotomous key is available in Griffiths, 1970. Although new species have been described since 1970, this key can be used to identify all known species found in association with bees.


The genus is cosmopolitan. Records from bees are from the Palaearctic and Oriental regions.

Bee hosts

Adults live in a variety of habitats, including bee nests (Apis and Bombus).

Host association level


associated exclusively with bees or their close relative, wasps; cannot live without these hosts


some life stages are associated with bees, while others are not

Facultative or opportunistic

can complete entire life cycle without bees or their close relative, wasps


Host associations, feeding, and dispersal

  • These mites live in various habitats (including bee nests), where they feed on decomposing organic matter and fungi.
  • Phoretic deutonymphs opportunistically attach to any arthropod carrier they can find nearby and use it for dispersal to a new habitat. Phoresy on adult bees has not been documented but is possible.
  • All stages can be found together in bee nests.
  • One species, Acarus immobilis, forms immobile, non-phoretic deutonymphs that can survive in adverse conditions.


The genus Acarus includes species that primarily inhabit nests of warm-blooded animals: mostly rodents and birds, but they are also peridomestic. These species are serious pests of stored products, primarily infesting grain and flour. Some species infest cheese (Fig. 15). Phoretic hosts include various arthropods (e.g., beetles, flies, fleas, and large mites).

Five species have been recorded from nests of European honey bee (Apis mellifera): Acarus farris, Acarus gracilis, Acarus immobilis, Acarus siro, and Acarus tyrophagoides. In addition, Acarus siro has been found in nests of Apis cerana and Bombus pascuorum. Acarus farris was the third most common species of Astigmata found in beehives in Poland (after Glycyphagus domesticus and Carpoglyphus lactis). In beehives Acarus species prefer pollen and bee bread, followed by bee hive debris. More rarely Acarus species occur on combs, wax, dead brood and bees, and mold. A few species can reproduce on propolis (A. immobilis) and honey (A. siro) but none on royal jelly (Chmielewski, 1991c).