This document proposes a method called Statistical-based Detection of Blackhole and Greyhole attackers (SDBG) to detect misbehaving nodes in delay tolerant networks. SDBG can detect both individual misbehaving nodes as well as nodes that are colluding together. It works by having each node record encounter data with other nodes, including the number of messages sent and received. Individual nodes that drop many messages can be detected based on having a low message forwarding ratio. Colluding nodes can be detected because they will have sent many messages to each other to fake good behavior. The method aims to accurately detect misbehaving nodes while keeping false positives low. Extensive simulations showed it can work well across different network conditions.