My daughter-in-law and grand-daughter have been handled to this sighting within the women’ toilet of an out of doors play centre within the New Territories of Hong Kong final weekend. This a is a Purple-necked Keelback, a snake that’s each venomous and toxic, however one which was regarded as neither for many years.
The species, now Rhabdophis subminiatus, was lumped in with our Grass Snake within the genus Natrix as innocent colubrid snakes. It’s now recognized that it’s a rear-fanged, venomous snake. There was at the very least one fatality and a variety of circumstances of extreme haemorrhage after folks have been bitten. Then it was found that the snake isn’t solely venomous, it’s, like all members of the genus, toxic too. It accumulates toxins from the toads it eats and shops them in glands within the neck, the nuchal glands. Any assault or strategy by a predator is met by the snake adopting one among three defensive posture during which the neck is pointed in the direction of or moved to contact the predator. For instance, the mouth is pointed downwards with the neck arched upwards.
The nuchal glands have been found in a Japanese species of the genus by Nakamura in 1935. Nakamura additionally realised the glands, which lie slightly below the pores and skin, produce one thing noxious. He was sprayed within the eye with yellow droplets as he decapitated the snake. He couldn’t fail to see the nice ache. Others, beforehand, had observed sore eyes after dealing with these snakes. Malcolm Smith (1875-1958), after he retired as home doctor to the royal family of Siam, studied the nuchal glands in a variety of species. They’re paired buildings which in some species prolong the size of the again in addition to the neck.
The glands are uncommon in that they don’t have any lumen for secretion to build up nor a duct to the outside. The yellow, foul-smelling secretion is shaped by breakdown of the secretory cells and in addition incorporates lymphatic and pigment cells. It’s simple to see how a predatory hen greedy the snake by the neck break the pores and skin and be confronted, in impact, by toad toxins. Nonetheless, breaking the pores and skin and damaging the nuchal glands is probably not the one approach for the secretion to be launched.
In 2011 Kevin Messenger, Daniel Rosenberg, Kevin Caldwell and William Sargent got here throughout a Purple-necked Keelback in a gap on the facet of a water catchment on Lantau island in Hong Kong. The snake after it had been caught, however not by the neck, arched its neck towards a glove after which secretion started to ooze from the area of the nuchal glands. How, with out ducts to the outside this was achieved isn’t recognized. Would contraction of the neck muscle tissue suffice? Is there a myoepithelium surrounding the glands which could contract? Is there a mechanically weak pathway to the outside for the secretion to succeed in the floor? What are the mechanisms offering defence towards, and transport from the intestine to the glands, of toad toxins? A lot stays to be found concerning the Purple-necked Keelback and others of its genus.
My grand-daughter was very fortunate to see the state of affairs of killing, feeding and getting maintain of defensive toxins. The toad, Duttaphrynus melanostictus, was not so fortunate.
Messenger KR, Rosenberg D, Caldwell KK, Sargent WL. 2012. Rhabdophis subminiatus helleri (Purple-necked Keelback). Defensive Conduct. Herpetological Overview 43, 497.
Mori A, Burghardt GM, Savitzky AH, Roberts KA, Hutchinson DA, Goris RC. 2012. Nuchal glands: a novel defensive system in snakes. Chemoecology 22, 187-198 DOI 10.1007/s00049-011-0086-2