An obligate parasite is a parasiticorganism that cannot live independently of its host.
References
Serge, Morand. et al. (1996). "Body size evolution of oxyurid (Nematoda) parasites: the role of hosts". Oecologia107 (2): 274–282. doi:10.1007/BF00327912.
Trontti, Kalevi, Aron, Serge and Sundström, Liselotte (2006). "The genetic population structure of the ant Plagiolepis xene - implications for genetic vulnerability of obligate social parasites". Conservation Genetics7 (2): 241–250. doi:10.1007/s10592-005-9003-y.