The physiological effects of resource allocation due to dietary restriction in spiders are poorly understood; in fact, the system-wide effects of any environmental stresses on spider physiology remain relatively unstudied. The aim of this study was to show the consequences of dietary restriction in the pholcid spider Physocyclus mexicanus Banks, 1898. Male spiders were fed either a high (ad libitum) diet (n = 43) or low (5–8 Drosophila melanogaster/week) diet (n = 32) through their penultimate instar. We found significant differences in testis volume, body mass, and tibia-patella length [TPL] between the two groups. Linear regression analysis reveals that the differences in testis volume between the two groups are not solely due to differences in body mass; for any given body mass, the low diet group has a smaller mean testis size than the high diet group. Our results suggest that P. mexicanus males allocate resources away from testis volume in times of scarcity.