In the described male and female, the abdomen is dark brown with lighter round patches and white hairs.
There are six short spines on top of the head. The carapace, long jaws and legs are reddish brown, with darker rings on parts of the legs.
Madagascarchaea rabesahala is a tiny spider with long jaws extending in front of its body. Its anterior median eyes rest on a prominent bulge. A small downward-pointing spine near the base of each jaw and the narrow, neck-like extension of the front body give it a distinctive profile.
The 2018 description examined variation in five males and four females. Total lengths were 1.56–1.66 millimetres in males and 1.91–2.07 in females. Mean lengths of the femur of the first leg, however, were 2.03 millimetres in males and 1.96 in females. In this sample, females had larger bodies while the mean length of this leg segment was greater in males.
A small spine between the lateral and anterior median eyes also varied. It was present in three of the five males and all four females examined. The male holotype lacked it. Rather than presenting just one individual as the species, the authors documented differences within the sample, using body size, leg proportions and the presence of spines as complementary observations.
An extinction-risk assessment has not been added yet.
The 2018 description reports material collected near Andranomay in 2000 and near Andasibe in 2009. Maintaining forest and its leaf-litter layer at documented collection sites, together with renewed surveys of occurrence, would help inform conservation planning for this species.