Family: Acaridae  - stored product mites 

Description:
Adults: Tiny, pale, translucent, slow moving, long hairs at rear, no antennae, four pairs of legs. Enormous numbers can occur in damp grain, residues, oilseeds and animal feeds. Mites are rarely found in large numbers in grain with moisture content below 14%. Other mites that occur in stores are predatory or parasitic.

Life cycle (Tyrophagus putrescentiae)
Optimum: 8.5 days at 32°C, 90% r.h.
Range:  8 - 36°C, 60 - 100% r.h.
Maximum population growth rate per month:  500 times.

Biology
Eggs:     Laid at random
Nymph:  Similar in appearance to adult but smaller
Adult:     Short lived, feeds, moves at a slow but steady pace.
 
 Note: Mites are arachnids (related to spiders) not insects.

Further information is contained in the article "Storage management: A range of control methods may beat grain pests"