The field of communications networks continues to emerge, thus leading to the rapid growth in the field of wireless sensor networks (WSNs). WSNs are noticeably different from traditional Ad hoc networks. The conspicuous difference between WSNs and traditional Ad hoc networks is that they (WSNs) are strictly constrained by limited supply of energy, capacity of storage, power of computation, and bandwidth. Because of these constraints and random deployment in some cases, it has become a challenge for the researchers to design a perfect routing layer protocol for wireless sensor networks. In this paper we studied the motivation and design issues for routing protocols in WSNs with the limitations of existing routing protocols for WSNs. We also used GloMoSim- 2.03 to find the shortcomings of traditional ad hoc routing protocols (DSR, WRF, AODV) when those are applied to WSN and to find out certain specific scenarios (considering low traffic networks and high traffic networks) of WSN where it is better to employ an existing Ad hoc routing protocol rather than developing a new one.