Collaborative wormhole attacks create links within MANETs, and unnel data to undesired destinations through the links. By doing so, wormholes compromise network performance, security, and may even bring down an entire network. We evaluate the impacts of collaborative wormhole attacks in MANETs, through simulations using AODV protocol in NS2. At first, we ran the simulation without collaborative wormhole nodes. We increased the number of nodes from 20 by an increment of 10 until 60 in every run. Every time we increased the node size, we ran the simulation 50 times and recorded the average. We then used the output collected to evaluate the average throughput and packet overhead. We repeated the same experiment with four collaborative wormhole nodes added to the network and collected results both for throughput and packet overhead. Our results show that there was a higher increase in throughput when no wormhole nodes were present than when collaborative wormhole nodes were introduced. For packet overhead, the simulations show that when collaborative wormhole nodes were added to the network, the packet overhead increased at a higher rate than when no wormhole nodes were present. The results show that collaborative wormholes negatively affect MANETs by reducing throughput and increasing packet overhead.