Semelparity is prevalent in arthropod species that exhibit maternal care. Previous hypotheses postulated that long-term maternal care constrains future reproduction in females, leading to the evolution of semelparity. Nevertheless, females may occasionally lose all or part of their offspring because of predation or other causes. Where females lose the first egg mass for any reason, the potential for females to produce an additional egg mass could be adaptive. This potential may be found widely among semelparous arthropods as a conditional strategy. We tested this hypothesis using the crab spider Lysiteles coronatus whose females guard their egg mass against predators. L. coronatus females did not consume food during the 40-d guarding period; this resulted in a 30.2% loss in their weight. When the females were separated from their eggs immediately after oviposition and were provided with food, they resumed feeding and their ovaries redeveloped. Dissection of guarding females indicated that their ovaries developed temporarily during egg guarding and that the developed ovaries were subsequently reabsorbed. These results suggest that the females maintain the potential to produce a second egg mass in case of egg loss, but that this potential declines towards the end of the guarding period. Field observations showed that a small fraction of the females oviposited in late July, when most females had completed egg guarding. The size of the late broods was similar to the oocyte numbers that we found in the females fed in the laboratory. This result suggests that a few females produced a second egg mass after they had lost the first one. Thus, we suggest that facultative second oviposition in L. coronatus females has evolved as an adaptation to egg loss, and that the development of ovaries during the guarding period is intrinsically programmed for compensatory oviposition.