New Zealand's Native Snakes

Yellow-bellied sea snake (Hydrophis platurus)

Most people believe that New Zealand is entirely free of snakes.  While that is largely correct, it is not entirely correct.  There are four species of snakes which have been found naturally in New Zealand.  All of them, however, are sea snakes.  The most commonly seen species is a type of hydrophiine sea snake, the yellow-bellied sea snake (Hydrophis platurus, formerly Pelamis platurus), while the other three species are all types of krait.

The hydrophiine sea snakes are a fully pelagic (ocean-going) species of snake which does not ever need to come to land for any reason and are much better adapted to life in the open ocean than the kraits.  They hatch their young live (viviparous), so they do not need to return to land to lay eggs.  Although they cannot drink salt water, they drink fresh water as it strikes the surface of the ocean during rainy periods before it has a chance to mix with the seawater.  As a result, they get all of their water requirements sorted while at sea (although they may go for months without water during long spells without rain and will become quite dehydrated).  They also have the end of their tail flattened to form a paddle-like surface to help them move more efficiently through the water.  The yellow-bellied sea snake is found over a very large area, through much of the tropical and some warmer parts of the temperate Pacific and Indian Oceans.  Although they are not common in New Zealand waters, between a half dozen to a dozen are found each year.  Nearly all of these snakes are found in the northern North Island, but they can be found as far south as the northern South Island on occasion.  Most of these snakes are found on the beach, which is not a place that a healthy yellow-bellied sea snake will ever be found.  If you should come across one it will be quite large, up to 62.5 cm long.  It is best to leave it alone; apart from the fact that they and the kraits are all considered native wildlife and so it is illegal to disturb them, they also have quite a potent venom.  They rarely bite people, but better safe than sorry, especially as it is unlikely that appropriate antivenom will be readily available.  As with the other snakes found in New Zealand, the yellow-bellied sea snake can't survive in waters colder than ~18 °C, so snakes arriving in New Zealand are typically not particularly happy about their situations and many of them die soon after.  It will be interesting to see if and/or how that changes as climate change progresses.

The kraits are well adapted to swimming through the ocean but lack some of the pelagic adaptations of the sea snakes.  They have to return to land to lay their eggs (oviparous) and are regularly found on land, where they need to return regularly to drink fresh water.  Three species of kraits have been found in New Zealand in the past.  The most common is the banded/yellow-lipped sea krait (Laticauda colubrina).  While this species is the most commonly seen of the krait species in New Zealand, it has only been seen here six times.  The other two species, Saint Giron's sea krait (Laticauda saintgironsi) from New Caledonia and the Loyalty Islands and the common/blue-lipped sea krait (Laticauda laticaudata) are each known from only a single record.  This is not surprising, as the kraits are tied to land far more than the yellow-bellied sea snake, so you would expect them to wander far from home far less frequently.

Banded krait (Laticauda colubrina)

What is the take-away from all this?  There are definitely snakes in New Zealand, but unless you are extremely lucky you will never see one, and you certainly do not need to worry about snakes while hiking through the forest.  Your best bet for seeing snakes is still taking a flight across the Tasman to Australia.

Here are the references that I used; I highly recommend them.  Click them to go to their home on the internet:

Lillywhite, H. B., Babonis, L. S., Sheehy III, C. M., & Tu, M.C.  (2008). Sea snakes (Laticauda spp.) require fresh drinking water: Implication for the distribution and persistence of populations. Physiological and Biochemical Zoology, 81(6):785–796. https://doi.org/10.1086/588306

Lillywhite, H. B., Sheehy III, C. M., Brischoux, F., & Grech, A.  (2014). Pelagic sea snakes dehydrate at sea. Proc. R. Soc. B, 281. http://dx.doi.org/10.1098/rspb.2014.0119

Lillywhite, H. B., Sheehy III, C. M., Heatwole, H., Brischoux, F., & Steadman, D.  (2017). Why are there no sea snakes in the Atlantic? BioScience, 68(1): 15-24. https://doi.org/10.1093/biosci/bix132

Rayner, Matt and Dix, Kelly. Sea snakes and kraits in New Zealand. Auckland War Memorial Museum - Tāmaki Paenga Hira. First published: 24 November 2015. Updated: 19 April 2016.