Although the house dust mite lives for only three months, as a species it has been on the earth for over 23 million years. It is a scavenger of organic matter, living or decayed. As an efficient scavenger the house dust mite considers its droppings as a source of future nourishment. The nourishment comes from discarded, ‘hard to digest’ food put into parcels by the mite´s gut and then encased in a dropping. Outside the body of the mite, active enzymes go to work to break down stubborn organic matter for future mite food. This is a process that can go on several times, until the mite can smell that it is nolonger food.
A healthy mite can produce between 20 to 30 droppings a day. On a moist surface the dropping dissolves and spills out its contents including the active enzymes and the collected material of the food parcel which may be from fungi, bacteria, plant fibres, yeast and scales from insects and animals. Unidentified bacteria have also been noted growing prolifically on the wall of the midgut of the house dust mite. Cells from this area are shed regularly into the debris that makes up the mite’s droppings.
It is true to say that the mite does not bite, but the enzymes in its dropping are as effective as a bite because they are found as far from the original entry point as in the fluid surrounding unborn children. If the enzymes can travel that far, where could bacteria go£ Of the fungi that the mite eats, Aspergillus penicillioides (an allergen in its own right) can be found living in mite droppings. No recent accessible research can explain why this fungi survives or fully describe the contents of ‘wild’ mite faeces.
Reference
‘Micro organisms associated with the house dust mite Dermatophagoides’, Heinan Oh et al,’ Jpn. J Sanit. Zool. 1986, Vol. 37, No 3, p229-235 Bacteria noted in the gut of the mite: Bacillus spp., Staphylococcus spp., Gram-negative non-fermenting rods and Gram-positive coryneform rods. Fungi noted: Aspergillus spp., Penicillium spp., Cladosporium spp., Alternaria spp., Acremonium spp Paecilomyces spp., and yeasts.
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