Desert locusts alternate between solitary and gregarious lifestyles. In the solitary phase, locusts avoid conspecifics, have cryptic appearance and behavior, move slowly and eat restricted diets. In contrast, gregarious locusts are active, have bright color and attract other locusts. Phase changes are regulated by population density and are an adaptation to the desert environment where rain is unpredictable. Gregarious locusts are notorious pests, as they can accumulate into devastating swarms. Now, Jozef Vanden Broeck and colleagues report a central role for protein kinase A (PKA) in the transition from solitary to gregarious behavior in locusts (Proc. Natl. Acad. Sci. USA, published online 19 December 2011; doi:10.1073/pnas.1114990109). Within 4 h of crowding, solitary locusts attain several key characteristics of gregarious behavior. The authors found that solitary locusts treated with a PKA inhibitor, KT5720, remained solitary after crowding. The authors performed RNA interference (RNAi)-mediated knockdown of a regulatory R1 subunit of PKA, which normally leads to the inhibition of PKA function, and found evidence of increased gregarious behavior. Injecting already-gregarious locusts with the KT5720 inhibitor did not induce a change to solitary behavior, which shows that gregarious behavior does not depend on PKA activity. Instead, these findings suggest a role for PKA in learning, or acquiring, gregarious behavior.