The Javan spitting cobra (Naja sputatrix), one of the snakes I wanted to encounter most in the Lesser Sundas. I had never seen a cobra in the wild before, much less a spitting cobra, so just thinking of one hooding up and standing tall to face me seemed surreal. We had seen well over our fair share of pit vipers, but after countless hours of walking through the dry forest our chances of a cobra became slimmer and slimmer. We had heard our guide muttering “cobra” and other Indonesian words that sounded exactly like cobra (but evidently were not) with his friends for the past week, and I kept joking with James about how triggered we were by the dialogue.
Sphenomorphus forest skinks were extremely abundant and could be heard dashing and darting constantly as we trudged through the bush. I picked out a faint continuous slithering sound in the leaf litter, and sure enough about four meters to my right was the cobra. Clearly the cobra had already noticed me and was darting for an escape. I shouted “cobra” urgently for everyone to come over and so our guide could have a go at grabbing the snake before it would disappear under a refuge in mere seconds. Certainly a different kind of encounter than the vipers I’m more accustomed to!
Javan spitting cobras are endemic to the Lesser Sundas and are one of over 15 species of cobra that spit venom (plus rinkhals, Hemachatus haemachatus). Spitting cobras have a small opening near the tip of the fangs and contract the venom glands to fill and increase pressure in the channel. Paired ridges line the bent channel and create vortices that whirl venom towards the orifice, minimizing pressure loss. The discharge orifice is positioned distally and forward-facing, allowing venom to flow downward through the channel resulting in rapid expulsion outward from the orifice. In fact, spitting cobras have a more circular orifice than non-spitting cobras, providing a more concentrated area for high velocity of venom ejection.
What is remarkable is the targeting and degree of accuracy with which these cobras shoot venom. Facial cues are used in orienting their defensive display, and the cobras aim the discharge towards the center of the face. Venom expenditure is without a doubt costly to snakes, and in the case of shooting venom only direct contact with the eyes is pain-inducing. Therefore, movement tracking and accuracy are crucial for this antipredator adaptation to persist. In some species, venom release is accompanied by quick rotational head movements that may help increase the spatial distribution of venom streams to have greater chances of a successful hit. Watch some awesome high definition footage by The Natural History Museum here. The video provides info on how African and Asian clades have independently evolved the venom spitting behavior and how this adaptation may influence the evolution of defensive toxins.
Links to papers here if you’d like to explore venom spitting in much more detail: (1) flow in the venom channel, (2) spatial dispersal of venom, (3) functional morphology of venom spitting.
As I moved around the cobra it would lock eyes with me, tracking me steadily and waiting for the opportune moment if I stepped a bit closer. This behavior reminded me of the frilly deimatic display — orienting the frill perfectly to face my eyes, hissing and lunging when I made any movement.