The anatomy of the gaster of Trichosurolaelaps crassipes is illustrated. Protonymphs, deutonymphs and adults were all seen with a scarlet gut and gave strongly positive results to occult blood tests. Host blood cells were identified in a gut smear from a female mite. An adult female gut could hold about 7.1 x 10-6 ml. The mite was seen frequenting small open skin lesions. Gram-negative bacteria identified in the mite`s gut are most likely to be endosymbionts. Mite larvae have their gastric caeca invaded by these bacteria before birth. There is a potential for this mite to act as a weak vector of disease from one possum to another.