Asian clam (Corbicula fluminea) is one of the most important nonnative aquatic invasive species in the freshwater ecosystem of North America, rapidly spreading in lakes, canals, streams, and rivers. This species has remarkably distinct mobility patterns in different phases of its life cycle. We formulate a novel mathematical model, in the form of nonlocal and time delayed partial differential equations, to calculate and characterize the invasion speed. The model system is lack of compactness due to the immobility of adult clams and the invasion speed may not be linearly determinate due to the hermaphroditic nature of clams. This talk is based on joint works with Kunquan Lan, Gunog Seo, Jianhong Wu, and with Xiaoqiang Zhao.