Experiments examined the accepted modes of action of the desiccant dust, diatomaceous earth (DE), against the flour mite, Acarus siro (L.) (Astigmata). Adult mites were exposed to three DE products for periods of 3, 18 and 72 h under conditions designed to allow partial desiccation of the mites without causing mortality. After exposure, the DE dust particles were washed off the mite bodies, and both the DE and the mites were examined for presence of cuticular hydrocarbons by gas chromatography-mass spectroscopy (GC-MS) analysis. GC-MS identified seven major cuticular lipids of chain length C(13)--C(26) that may have a role in the waterproofing of A. siro. After 18 h exposure, n-tridecane and several different long-chain fatty acid ethyl esters were detected on one of the DE products. After 72 h, n-tridecane was detected on all three DE products. Mite samples retained after removal of the DEs were examined by microscopy. Tentative evidence was observed by conventional low-power microscopy that might indicate uniform removal of the epicuticle. However, a detailed examination by scanning electron microscopy showed no signs of abrasion.