For some time I have suspected that spruce needles were eaten out by Oribatoid mites. h recent lot of spruce litter from the Great Smoky Mountains (North Carolina-Tennessee) made possible this investigation with the following results.Firm, undecomposed needles hold no mites. They are first acted upon by fungi which reduce the cell contents and a good deal of the mesophyll. In this condition the needles are soft and punky. It is only then that the mites are able to lay their eggs in the needles. Most punky needles examined sheltered an immature Phthiracarid mite (October 28th), sometimes two. These mites were found at one end of their excavation, having left behind them a completely dismanted needle and a litter of faeces. They leave the walls intact so that each of these soft, white mites is completely sheltered within its needle. The last molt is effected intra muros. Adults may thus be found within an undamaged needle. When hard and brown the adult cuts its way out and seeks a mate in the wide, moist world of the lower litter layer. The entire life of such a species is thereiore spent in the one horizon of the forest floor (the F2 layer). The leaf is left, a thin walled tube, its central stele and sclerenchymatous tissues completely eaten out and reduced to a thin litter of minute faeces (less than 0.1 mm. long).