Prehensile-tailed Skink

The Solomon Islands skink, also called the monkey-tailed or prehensile-tailed skink, is the largest known living skink. It is an arboreal lizard endemic to the Solomon Islands archipelago, living in the upper canopy, often in strangler fig trees, where an adult usually keeps a territory in one tree. Adults can reach 81 cm in total length, more than half of it tail. Dark green and speckled, it uses its fully prehensile tail as a fifth limb. It is entirely herbivorous, eating fruits and vegetables including pothos, and is mostly active at dusk and dawn. It lives in family groups called a circulus and is hostile to outsiders.

About the prehensile-tailed skink

The prehensile-tailed skink, also called the Solomon Islands skink, monkey-tailed skink, or zebra skink, is an arboreal lizard found only on the Solomon Islands archipelago and in Papua New Guinea. It is the largest known living species of skink, with adults reaching a total length of up to 32 inches (81 cm), more than half of that made up of tail. The genus Corucia contains only this one species, and its closest living relatives are the blue-tongued skinks of the genus Tiliqua and the Egernia skinks of Australia, New Guinea, and Indonesia — all part of the same reptile subfamily, Lygosominae.

The body is long and slender, carried on strong, short legs, with a triangular head and small round eyes. The jaw is strong enough to crush plant material, though the teeth themselves are small, suited to a herbivorous diet rather than to catching prey. Scales run dark green, often speckled with light brown or black on top, fading to light yellow or green underneath. Every toe ends in a thick, curved nail built for gripping bark and branches. The tail is fully prehensile — the animal uses it as a fifth limb, wrapping it around branches for support as it moves through the canopy, which is where three of its common names referencing "monkey" or "prehensile" tails come from.

Two subspecies are recognized. The common monkey-tailed skink (Corucia zebrata zebrata) lives on the islands of Choiseul, New Georgia, Santa Isabel, Guadalcanal, Nggela, Malaita, Makira, Ugi, and Owaraha, and is the larger of the two, with males averaging 28 inches (71 cm) and the subspecies as a whole weighing around 850 grams (1.87 lb) on average. The northern monkey-tailed skink (Corucia zebrata alfredschmidti), found on Bougainville, Buka, and the Shortland Islands, is smaller, weighing closer to 500 grams (1.1 lb), and can be told apart by its black eye sclera, larger dorsal and ventral scales, and seven parietal scales instead of the usual five.

Behavior and diet

The prehensile-tailed skink is crepuscular, most active in the low light of dusk and, to a lesser degree, dawn, and it does most of its feeding at dusk. Its eyesight is sharp enough to spot both food and threats, but it relies just as heavily on smell, flicking its tongue to gather scent particles and pressing them to a Jacobson's organ at the roof of its mouth — a technique it shares with snakes. Adults typically stake out a territory within the canopy of a single tree, often a strangler fig, and both sexes defend that space, behaving with hostility toward skinks from outside their own family group.

That family group, called a circulus, is one of the more unusual traits of this species: the prehensile-tailed skink is one of only a few reptiles known to live in a stable social unit rather than alone. Diet is entirely plant-based — leaves, flowers, fruit, and new shoots from a range of forest plants, including Epipremnum pinnatum, a species that carries levels of calcium oxalate toxic to many other animals but which this skink eats without apparent harm. Juveniles eat feces from adult skinks in their group to pick up the gut microflora they need to digest plant matter, and newborns eat their own placental sac after birth, not taking other food for their first two days.

Reproduction is equally distinctive for a reptile. The species is viviparous with a placenta, meaning the female nourishes her developing young directly rather than relying on stored egg yolk, over a gestation of six to eight months. The young are born large relative to the mother — one former reptile curator likened it to "a human mother giving birth to a six-year-old" — and single births are the norm, though twins and, in at least one recorded case, triplets have occurred. Newborns stay within the circulus for six to twelve months, protected not just by their parents but by other unrelated adults in the group, before moving off around age one to start a family group of their own.

Range and habitat

The prehensile-tailed skink is native to the Solomon Islands archipelago in the southwest Pacific and to Papua New Guinea, which politically includes Bougainville and Buka at the archipelago's northern end. Both subspecies live strictly in trees, generally in the upper canopy of forested habitat, and adults tend to claim a territory centered on a single tree. Strangler fig trees are a favored home as long as the epiphytic plants the skinks feed on are also growing there. The species also turns up in semi-cleared areas and cultivated food gardens, provided its food plants are present.

Extensive logging across the Solomon Islands has cut directly into this canopy habitat and is described as a serious ongoing threat to the species' survival, compounding pressure from hunting and collection for the pet trade.

Conservation status

The prehensile-tailed skink is classified as Near Threatened (NT). Its wild populations have been reduced by a combination of pressures: extensive logging removes the forest canopy it depends on, it has long been consumed for food by Solomon Islanders, and demand from the international pet trade has driven heavy collection. Because of the volume of animals being exported, the small area the species is native to, and its low reproductive rate — typically a single offspring per multi-month pregnancy — the species was placed on CITES Appendix II in 1992, which limits how many animals can be traded commercially between countries.

There is no regulation curbing the pace of deforestation in the Solomon Islands, and some herpetologists argue that limited, managed export to recognized institutions may actually help the species by supporting genetic diversity through captive breeding. Others note that captive breeding alone cannot carry the species, given how few offspring each female produces and how long each pregnancy lasts. The Philadelphia Zoo has maintained a breeding program for the past 40 years, though even there, slow growth and single births have made sustained breeding success difficult, and breeders have found that pairing skinks from different islands can sometimes produce unproductive matches.