Spider bites cause a range of symptoms from simple swellings to disfiguring necrotic lesions, and occasionally death. While spider bites are not a major medical problem in Korea, it would be of great value to know which species of spiders pose a threat to human health. A middle molecular weight protein, sphingomyelinase D, has been identified in the venom of the brown recluse spider and strong evidence suggests that they have a major role in spider bite necrosis. For the identification of necrotizing species, we have investigated using recently developed non-radioactive assay of sphingomyelinase for rapidly screening the necrotizing venoms. Here, we demonstrate the fetal toxicity of total 65 species (24 genera, 9 families) of the web-building spiders among 622 identified spider species in Korea. It has been revealed that four species of the orb-weaving spider, Araneus ventricosus (family Araneidae, 0.3509), Dipoena castrata (0.2413, family Theridiidae), Argiope minuta (0.1836, family Araneidae), and Paracoelotes spinivulva (0.1760, family Amaurobiidae) have relatively strong activities among themselves. However, comparing to that of the brown recluse spider, Loxosceles reclusa (1.814) in North America, the necrotizing shpingomyelinase activities of these Korean web-building spiders are still very low. Based on our results, we may thus conclude that there would be little possibilities in South Korea to create serious medical problems caused by necrotizing arachnidism.