Flour mite, grain mite Acarus siro

Key features

Acarus siro is around 0.5 – 0.7 mm in length.
It is white in colour with a pearly iridescence, its legs often have a brown or pink colouration. Its body is divided into two clear sections with a distinct line between the two sections known as the proterosoma (the anterior end) and the hysterosoma (the posterior section).This mite has two pairs of long setae protruding from the posterior end of the hysterosoma.


The female can live for around 40 days as an adult and during that time she can lay as many as 500 eggs. The small white eggs are deposited in the food and within 3 – 4 days the first stage larvae emerge. These are around 0.15 mm long and have three pairs of legs. They feed for a few days (4 – 5 days normally) and then prepare for moulting to the next stage, the first nymphal stage, which has four pairs of legs. There is then a second nymphal stage which moults to produce the adult. Total nymphal span is around 15 – 20 days.
The total life cycle from egg to adult can vary from as little as 30 days at 10-15″C to 140 days at TC. Temperature and humidity significantly influence the mite life cycle & mites rarely exist in a relative humidity of less than 65%. Mite populations can increase seven-fold each week and thus very heavy infestations may develop


Worldwide. Significance

Acarus siro is probably the most serious and frequently encountered mite pest of stored products. It is a pest of a wide variety of different kinds of products such as flour, grain, linseed, cheese, dried fruits, etc. Its presence in commodities often imparts a taint known as “mintiness” and this effectively renders such contaminated product unusable. Animals fed on mite-infested feed may develop digestive problems. Mites of this genus have been implicated in causing dermatitis, rhinitis, respiratory tract irritation and intestinal upsets.


For treatment of the infestation, remove and destroy any infested commodities. Reduce humidity in the property.
Acaricides may be used on the fabric of the building, skirting boards, floorboards. etc.
Reducing the moisture content of a commodity below 12% prevents mite development. Detection of an infestation may be difficult as the mites appear dust-like.

Illustration: Acarus siro adult.

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