Two species of Asian praying mantids, Tenodera angustipennis (Saussure) and Tenodera aridifolia sinensis (Saussure), which have become common to old fields in the northeastern United States, share a common resource base that raises the question of how they can coexist in the same habitat. We studied the reproductive output measured by numbers of oothecae of naturally established populations of these two species in an old field during 7 yr (2009–2015) of secondary succession. During the initial herbaceous vegetation-dominated stage, T. angustipennis oothecae were more abundant than those of its congener, but numbers steadily declined, until it had nearly disappeared by 2014. In contrast, numbers of T. a. sinensis oothecae increased from 2007 until 2014, and then sharply declined in 2015. The steady increase in abundance of this species throughout most of the successional development during the study may be owing to greater diversity of plant species used for oviposition. We believe that the most likely reasons for the continuous decline in T. angustipennis were a combination of intraguild predation by the larger T. a. sinensis, and egg parasitism by the wasp Podagrion mantis, which is not able to parasitize oothecae of T. a. sinensis. The later decline in T. a. sinensis may reflect the fact that the site had become dominated by trees, and neither of these species is typically found in forest habitats.