Languages differ in their behaviour while the constructor or destructor of an object is running. Slow bee paralysis virus is transmitted to hives through "Varroa destructor" mite infestations. "Varroa destructor", a parasitic mite, propagates within the brood cell of bees. Mites that cause disease in honey bees are described in "Varroa destructor". Usually that operation occurs within another destructor, typically the destructor of a smart pointer object. The mite "Varroa destructor" has become the largest single problem faced by beekeepers worldwide. The main cause of the decline was thought to be the parasite "Varroa destructor". Objects that may be deleted in this way need to inherit a virtual destructor. However, some object-oriented languages allow a custom destructor method to be implemented, if desired. A destructor should never throw an exception. Once infected with a "V. destructor" mite, the honey bee may be damaged two ways. The common yabby ("Cherax destructor") is an Australian freshwater crustacean in the Parastacidae family. On Kembel, the Daleks test the Time Destructor on delegate Trantis. Australian ravens sometimes eat yabbies ("Cherax destructor") from the edges of dams. The most common and widely distributed species in Australia is the common yabby ("Cherax destructor").