In zoology, an inquiline (from Latin inquilinus, "lodger" or "tenant") is an animal that lives commensally in the nest, burrow, or dwelling place of an animal of another species. For example, some organisms such as insects may live in the homes of gophers and feed on debris, fungi, roots, etc. The most widely distributed types of inquiline are those found in association with the nests of social insects, especially ants and termites – a single colony may support dozens of different inquiline species. The distinctions between parasites, social parasites, and inquilines are subtle, and many species may fulfill the criteria for more than one of these, as inquilines do exhibit many of the same characteristics as parasites. However, parasites are specifically not inquilines, because by definition they have a deleterious effect on the host species, while inquilines do not.
In the specific case of termites, the term "inquiline" is restricted to termite species that inhabit other termite species nest  whereas other arthropods cohabiting termitaria are called "termitophiles".
Inquilines are known especially among the gall wasps (Cynipidae family). In the sub-family Synerginae this mode of life predominates. These insects are similar in structure to the true gall-inducing wasps, but they do not produce galls, instead depositing their eggs within those of other species. They infest certain species of galls, such as those of the blackberry and some oak galls, in large numbers, and sometimes more than one kind occur in a single gall. Perhaps the most remarkable feature of these inquilines is their frequent close resemblance to the insect that produces the gall they infest.
Other inquiline species include Vespula austriaca (its common host being Vespula acadica) and Dolichovespula adulterina (its common hosts being Dolichovespula norwegica and Dolichovespula arenaria, both true wasps, and Bombus bohemicus, a cuckoo bumblebee.
The term inquiline has also been applied to aquatic invertebrates that spend all or part of their life cycles in phytotelmata, water-filled structures produced by plants. For example, Wyeomyia smithii, Metriocnemus knabi, and Habrotrocha rosa are three invertebrates that make up part of the microecosystem within the pitchers of Sarracenia purpurea. Some species of pitcher plants like the Nepenthes and Cephalotus produce acidic, toxic or digestive fluids and host a limited diversity of inquilines. Other pitcher plant species like the Sarracenia or Heliamphora host diverse organisms and depend to a large extent on their symbionts for prey utilization.
- Florencio, Daniela Faria; Marins, Alessandra; Rosa, Cassiano Sousa; Cristaldo, Paulo Fellipe; Araújo, Ana Paula Albano; Silva, Ivo Ribeiro; DeSouza, Og (2013-06-21). "Diet Segregation between Cohabiting Builder and Inquiline Termite Species". PLoS ONE. 8 (6): e66535. doi:10.1371/journal.pone.0066535. PMC . PMID 23805229.
- Rines, George Edwin, ed. (1920). "Inquiline". Encyclopedia Americana.
- Discover Life: Family Cynipidae: Subfamily Synerginae visited 1 January 2011
- Schmidt, J.O; Reed, H.C; Akre, R.D (1984). "Venoms of a Parasitic and Two Nonparasitic Species of Yellowjackets (Hymenoptera: Vespidae)" (PDF). Journal of the Kansas Entomological Society. Retrieved October 14, 2014.
- Carpenter, James (16 March 2006). "Phylogenetic Relationships among Yellowjackets and the Evolution of Social Parasitism (Hymenoptera: Vespidae, Vespinae)". American Museum Novitates.
- Dvorak, L. (2007). "Parasitism of Dolichovespula norwegica by D. adulterina (Hymenoptera: Vespidae)". Silva Gabreta.
- Cronk, J. K.; Fennessy, M. Siobhan (2001). Wetland Plants: Biology and Ecology. p. 145.
- Cochran-Stafira, D. L. and von Ende, C. N. (1998). Integrating bacteria into food webs: studies with Sarracenia purpurea inquilines. Ecology, 79(3): 880–898.
- Adlassnig, W., Peroutka, M., & Lendl, T. (2011). Traps of carnivorous pitcher plants as a habitat: composition of the fluid, biodiversity and mutualistic activities. Annals Of Botany, 107(2), 181–194.