Due to mobility, spontaneous networks composed of nodes following similar group mobility patterns are likely to overlap. Previous solutions invariably considered overlapping as a permanent state where the networks combine to form a new network. In this paper, we propose a more realistic model where merging is either permanent or transient. Our contributions are twofold. First, we introduce a methodology to identify transient merging and detect implicit permanent merging. Second, we propose an efficient routing protocol between merging networks while in the transient state. Our approach is completely distributed and incurs low routing control overhead. We also investigate a solution to prevent respective intra-network communications from interfering.