Read the discussion of snakes’ handling prey and invariably the author will make a statement about snakes swallow their prey whole. Also, there is often a statement about that the size of the prey the snake can swallow is dependent upon the snake’s ability to gape its jaws. Thus, snakes are frequently referred to as gape-limited predators.
Until recently there were two known exceptions to this in the advanced snakes, and they are sister species in the family Homalopsidae. Also, the two species are sympatric in Southeastern Asia’s coastal marine environments. Gerard’s Water Snake, Gerarda prevostiana was reported by Jayne et al. (2002) to take crustaceans that have recently molted and rip them into bite-sized pieces by pulling the crustacean through a loop of their body. The behavior makes it possible for Gerarda to swallow prey much larger than would otherwise be possible if it had to swallow the crab whole. Further study of Gerard’s Mud Snake lead Jayne et al. (2018) to investigate the gape of the three the snake species, all members of the same clade, that share the unusual diet of decapod crustaceans. Fordonia leucobalia eats hard-shelled crabs and had maximal gape similar to a piscivorous relative the Dog-faced Water Snake, Cerberus schneiderii. However, both Gerarda prevostiana and Cantoria violacea eat freshly molted crabs and snapping shrimp, respectively, and their maximal gape was significantly smaller than the Dog-faced Water Snake, Cerberus schneiderii and the Crab-eating Snake, Fordonia leucobalia. From smallest to largest prey size consumed relative to maximal gape, the rank order was F. leucobalia, Cantoria violacea and G. prevostiana. Unusual specialized behaviors included: (1) a closed-mouth strike and using the chin to pin the crabs (F. leucobalia), (2) breaking off crab legs (F. leucobalia, G. prevostianta) and (3) ripping apart the crab carapace aided by body coiling (G. prevostiana). Behavioral innovations and choice of prey allowed G. prevostiana to consume crabs two to four times larger than their maximal gape area and handle prey approximately nine times faster than F. leucobalia. The authors note that this is a striking example of how the evolution of specialized behaviors can improve performance and circumvent anatomical constraints on prey size.
The poorly known Cantor’s Mangrove Snake, Cantoria violacea, has also been recently caught in the act of feeding in the field. Ghodke et al. (2018) found Cantoria using their bodies in a press-and-pull manner to tear off the claws and most of the legs before swallowing the cephalothorax. Swallowing took about 10 minutes. In one instance, a large crab approached and touched a feeding snake. They speculate that the second crab might have been an opportunistic scavenger. This species had been previously reported to eat pistil shrimp (Voris and Murphy, 2002) which were swallowed whole. The authors suggested that C. violacea might employ different strategies to deal with hard- and softer-bodied different prey, although we cannot rule out the possibility that dismembering hard-shelled crabs is merely an unintentional consequence of the snake maneuvering the narrow end of the crab toward its mouth. You can see some video of these snakes feeding below.
A second clade of mostly semi-aquatic and aquatic snakes, the natricids (family Natricidae) also has members that eat crustaceans. In the USA, Graham’s Crayfish Snake, Regina grahamii and the Queen Snake, Regina septemvittata along with the Striped Crayfish Snake, Liodytes alleni, the Black Swamp Snake, Liodytes pygaea, and the Crayfish Snake, Liodytes rigida. Some of these east newly molted crayfish and others hard-shelled crayfish. None have been observed dismantling their prey.
However, Noonloy et al. (2018) reported a freshwater Asian natricid, in the genus Opisthotropis cf. spenceri tearing up soft-shelled crabs (Larnaudia chaiyaphumi) in a Thai stream. Opisthotropis are poorly known species most live in streams and much remains to be discovered about their natural histories.
Ghodke S, Chandi M, Patankar V. 2018. Yellow-banded Mangrove Snakes (Cantoria violacea) Consume Hard-shelled Orange Signaler Crabs (Metaplax elegans). IRCF Reptiles & Amphibians 25(1):50–51.
Jayne BC, Voris HK, Ng PK. 2002. Herpetology: Snake circumvents constraints on prey size. Nature 2002 418(6894):143.
Jayne BC, Voris HK, Ng PK. 2018. How big is too big? Using crustacean-eating snakes (Homalopsidae) to test how anatomy and behaviour affect prey size and feeding performance. Biological Journal of the Linnean Society 2018 Feb 26;123(3):636-50.
Noonloy T, Kunya K, Chanhome L, Sumonth M, Chomngam N, Pauwels OSG. 2018. Crab-ripping: An Unusual Feeding Behavior Newly Recorded in Freshwater Snakes. Bulletin of the Chicago Herpetological Society 53(3):53-56.
Voris HK, Murphy JC. 2002. The prey and predators of homalopsine snakes. Journal of Natural History. 36(13):1621-32.