Parental care entails physiological costs to the mother. These costs, even if dramatic, are usually reversible and do not result in mortality of the mother. In the spider Stegodyphus lineatus Latreille 1817 (Eresidae), maternal care is extreme and irreversible: mothers regurgitate food for the young and then die when consumed by them (matriphagy). We examined whether the mother's midgut tissues undergo structural changes in preparation for regurgitation and matriphagy. Our histological data show that the midgut diverticula (MD) tissues start to degrade during the egg sac incubation period. When the young emerge from the egg sac, the midgut tissues are partly liquefied and are retained within the MD. The degradation process intensifies when the female feeds her young by regurgitation and liquid tissue is observed within and among the diverticula lobes. The presence of the lumen of a diverticulum during the regurgitation process suggests that degenerated tissues enter the lumen and form the regurgitated fluid. At matriphagy, the abdomen is filled with liquid containing nutritional vacuoles, which the young imbibe after piercing the female's abdomen. We conclude that the MD undergoes a gradual degradation process that maximizes the nutritional potential of the female's body and finally enables complete consumption of her soma. These changes are consistent with the extreme semelparous reproductive system of S. lineatus, where a female invests all of her resources into a single reproductive event. This is the first demonstration of the mechanism underlying suicidal maternal care in an arthropod.