Closely related spiders often exhibit similarities in traits such as development, morphology and behaviour. Here, we compared development, adult body size and reproduction in two closely related spiders, the rabbit hutch spider, Steatoda bipunctata, and that triangulate cobweb spider, S. triangulosa (Araneae: Theridiidae). Both species are native to Eurasia and synanthropic, often co-occurring in the vicinity of human habitation. Development time from neonate to adult was similar in both species. Both species exhibited sexual-size dimorphism, where females were larger than males. Although females were also approximately the same body size, male S. bipunctata were significantly larger than male S. triangulosa. Mean brood sizes were also larger in S. bipunctata than S. triangulosa over the first seven egg sacs. Our results show that some traits in these two species overlap considerably, but with some differences such as in the degree of sexual size dimorphism and male morphology.