This paper proposes an ant-inspred backoff-based opportunistic routing protocol which optimizes the forwarding area based on the concept of ant colony optimization. In the traditional backoff-based opportunistic routing protocols, they may increase unnecessary packet forwarding to expand the forwarding area since a receiver of data packet autonomously participates the packet forwarding. Hence, to deal with the forwarding area expansion, the proposed method suppresses the potential forwarders to adjust the backoff time based on their pheromone levels. Finally, this paper clarifies the performance of the proposed method in comparison with the conventional method using computer simulations. The results show that the proposed method can reduce the network resource consumptions and the end-to-end delay while keeping higher packet transmission success rate.