Malacosoma americanum (F.) (Lepidoptera: Lasiocampidae) was recently implicated in early fetal losses and late-term abortions of pregnant mares in the thoroughbred and saddlebred industry centered in central Kentucky. The direct role of the caterpillars in these losses prompted the need for a more thorough understanding of life history and age-specific biology, to develop more precise management strategies and reduce future losses. During 2003 and 2004, egg masses and tents were destructively and sequentially sampled, respectively, to observe development and mortality agents. Eggs were significantly impacted by parasitization. Larval development was linear, yet asynchronous, with individual tents containing up to four instars simultaneously. Predators were the major mortality factor impacting the first three instars; parasitoids and pathogens had the greatest impact on fourth, fifth, and sixth instars. These data demonstrate that the eastern tent caterpillar is impacted by a variety of biotic mortality agents throughout the Bluegrass region of Kentucky, and the potential impacts on natural enemies must be considered when designing any direct suppression strategies targeting populations.