Spitting behaviour in the Chinese cobra Naja atra

This study describes the ability of a captive Chinese cobra (Naja atra) to spit venom and presents a video analysis of a strike and spit manoeuvre. However, among the many specimens of N. atra raised by the author only the female examined in this study regularly displayed spitting behaviour, and then only within the confines of its terrarium. Fang morphology of N. atra was investigated by microscopy and compared with that of a ‘true’ spitting cobra, Naja sputatrix. The results show that N. atra does not have specially modified fangs so that venom is ejected downwards from the fangs, not forwards. Consequently, to direct venom at a target requires a specific manoeuvre involving a forward lunge and head rotation. This arrangement is very similar to that described for Naja kaouthia and suggests that the evolution of spitting behaviour could precede the development of specialised fangs that refine the action. Figure 1. Adult female N. atra, the protagonist of this study (with a congenital groove in the ventral scales seen close to where the snake’s body reaches the substrate) Spitting behaviour in the Chinese cobra Naja atra Herpetological Bulletin 148 (2019) 23 capture the specimen’s spitting behaviour, a digital camera (Nikon Coolpix P510) was positioned inside her terrarium and set on to records video at 120 frames per second. To optimise the results captured by the lens, dark cardboard panels and additional lights were applied inside and outside the terrarium which measured 120 cm long, 60 cm deep and 50 cm high. To visualise the traces of venom following a spit, sheets of A4 paper of different colours (red, yellow, blue or green) were used as targets although no one colour caught the attention of the cobra more than another. Before each filming session, the glass front of the terrarium was removed and then, as soon as the cobra’s attention had been caught by my person (full visor protection and protective gloves were used), a paper target was placed at the same height as the terrarium directly in front of the cobra. The maximum distance set between the terrarium and a target was 40 cm. For an examination of the fangs by microscope, a fang was collected directly from the mouth of one of the female’s offspring (hatched 2016), sired by a male sibling from the same clutch. The fang was removed carefully from the live snake while no longer fixed to the maxillary bone. Microscope pictures of the fang were taken using a stereomicroscope (Nikon SMZ645). The sample was placed in a Petri dish containing distilled water, and the images were taken through the object when laid on a solid surface and also when suspended in distilled water. For comparative purposes, the same procedure was applied to the fangs of an adult female Indonesian spitting cobra Naja sputatrix, Boie, 1827, collected from a deceased adult female bred in captivity (for details of the snake’s lepidosis see Supplementary Material). Fang measurements were taken using a digital calliper (accuracy ± 0.005 mm). Tinting of discharge orifices and venom canals in images of the fangs was possible due to the double illumination and the suspension of the fangs during microscopy. This technique conferred transparency to the fangs making the discharge orifices, venom canals and liquid within them clearly visible.