Wireless Sensor Network (WSN)s are now a days most widely used and are undergoing many security threats. Of the different types of threats, Jamming attack has been considered a severe security threat. These jamming attacks cause the overutilization of scarce resources like the battery power. Further, high computations require lot of memory. Such problems cause the reduction in the lifetime of the sensor nodes in WSNs. There are four types of jamming attacks in which the most difficult type of attack is the reactive jammer as it is easy to launch by the adversary but very difficult to detect and defend. In this paper we present a brief survey of the types of jamming attacks, methods used to detect and defend the jammers.