The male of Callobius balcanicus resembles C. claustrarius in having the similar conductor, distal embolus, and massive tegular apophysis but can be distinguished by the bigger palp, bigger and different kind of tegular apophysis (much more hook formed by C. claustrarius) and longer and slightly twisted prolateral tibial apophysis in C. balcanicus.
prosoma length: 3.9 mm, prosoma width: 2.9 mm.Body length male: 8-9 mm
The female can be easily recognized by the longer epigynal and tapering lateral lobes in C. balcanicus. Vulva with big elliptical receptacles.
prosoma length: 4.5 mm, prosoma width: 3.0 mm.Body length female: 10-12 mm
Blagoev G, Deltshev C, Lazarov S, Naumova M (2018) The spiders (Araneae) of Bulgaria. Version: August 2018. National Museum of Natural History, Bulgarian Academy of Sciences. Online at http://www.nmnhs.com/spiders-bulgaria/ (accessed on 10.9.2018)