Nephrurus, Knob-tailed geckos Nephrurus vertebralis. Knob tailed geckos in the genus Nephrurus pose an enigma to biologists. All possess a curious small knob at the end of their tails whose function remains completely unknown. These lizards engage in a threat display when they hiss and lunge with an open mouth. Like the majority of geckos, all members of this endemic Australian genus are nocturnal insectivores. These handsome geckos have very large, puppy dog like, eyes. Nephrurus laevissimus. All seven known species are terrestrial and all occur in the arid zone. They prey on nocturnal arthropods, especially scorpions, spiders, beetles, crickets and cockroaches. Like most geckos, they lay two eggs. One species, vertebralis, occurs in shrub-Acacia "mulga" habitats, two species are associated with rocky outcrops (asper and wheeleri), two tend to be associated with sandy plains (levis and stellatus), while two others are restricted to sand dunes or sandridges (deleani and laevissimus). Nephrurus levis.