Explanatory Essentialism (EE) is the view that a property is the essence of a kind because it causally explains the many properties that instances of that kind exhibit. This paper examines an application of EE to biological species, which I call Biological Explanatory Essentialism (BEE). BEE states that a particular biological origin is the essence of a species on the grounds that it causes certain organisms to display the group of properties the species is associated with. Evaluating BEE is important, (...) as it offers a novel argument for biological essentialism—the contentious claim that biological species have essences. This paper critically assesses the empirical foundations of BEE, focusing on the presupposition that a single biological origin causes the many properties associated with the species in question. By discussing a case of cryptic species among five-toed jerboas within the Scarturus elater species complex, I challenge that presupposition, thereby arguing that cryptic species present a serious obstacle to BEE. I conclude that BEE fails to support biological essentialism and suggest that essentialist philosophers reconsider the role of causal-explanatory factors in accounting for the purported essences of biological species. These philosophers may need to explore alternatives beyond such factors, one of which I briefly outline. (shrink)