Madagascar Giant Day Gecko

The Madagascar giant day gecko is a diurnal, tree-dwelling lizard native to tropical and subtropical forest in northern and northwestern Madagascar. It reaches a total length of 9–11 inches (23–28 cm), and females are generally smaller than males. The body is bright green, with a red stripe from nostril to eye and often red dots or bars on the back. It feeds on insects and other invertebrates, occasionally on small vertebrates, and also licks soft sweet fruit, pollen and nectar. Males are quarrelsome and territorial and admit only females to their territory. It has been introduced to places such as Florida, Hawaii, Reunion Island and Mauritius.

About the Madagascar giant day gecko

The Madagascar giant day gecko is a large, bright green lizard from the forests of northern Madagascar. It belongs to Phelsuma, a genus of more than 70 day gecko species and subspecies that, unlike most geckos, are active in daylight. It lives in trees and feeds on insects, nectar and fruit.

Its scientific name is Phelsuma grandis. The genus honors the Dutch physician Murk van Phelsum, and grandis is Latin for "great," a nod to its size. Until 2007 it was treated as a subspecies of the Madagascar day gecko, Phelsuma madagascariensis. That year researchers raised it to a full species after environmental niche modeling showed clear, consistent differences from its relatives, and later genetic work has backed that decision.

It is a big gecko. Adults reach 23–28 cm (9–11 in) in total length, toward the top of the day gecko range of roughly 6.5 to 30 cm (2.6 to 11.8 in). Females are generally smaller than males.

The color is what most people notice. The body is bright green, or rarely bluish green, and a red stripe always runs from the nostril to the eye. The back usually carries red dots or bars, though these markings vary a great deal and are sometimes missing altogether. Some animals have small blue spots. The belly ranges from creamy white to an egg-yolk yellow. Young geckos show much more red than adults, and many of those markings fade with age. When stressed, the whole animal darkens to a deep green and the red on its face and back turns more orange.

Look closely at an adult's neck and you may see bulging sacs on the sides. These are calcium stores. Across the day gecko genus, the sacs are most often well developed in females, which need the calcium to produce eggs, while males have well-developed femoral pores on the underside of the hind legs.

Behavior and diet

Day geckos are diurnal, and the giant day gecko spends its days in the trees. Like other members of its genus, it climbs with toe pads made of tiny plate-like lamellae that let it walk up vertical and even upside-down smooth surfaces such as bamboo or glass. It usually moves slowly but can dash away very fast when startled, and it has a reputation for escaping enclosures.

Like most other geckos, it has no eyelids. Instead, a clear, fixed scale covers each eye, and day geckos keep it clean by licking it with the tongue; the giant day gecko licks its eyes often.

Males are quarrelsome and territorial. A male will not tolerate other males nearby and allows only females into his territory. In captivity, where a female cannot get away, a male may even wound her seriously, and the two have to be separated. Courtship involves shaking the tail or body and vocalizing. A female that rejects a male may turn a darker green.

The diet is a mix of animal and sugary foods. Giant day geckos eat a variety of insects and other invertebrates, and occasionally small vertebrates. They also lick nectar, pollen and soft, sweet fruit. Studies show they prefer red or yellow nectar, a preference that appears to be inborn. Both wild and captive geckos have been seen eating their own young.

Breeding runs from December to June. During this season a female can lay several pairs of eggs, and the young hatch after about 48–80 days, depending on temperature. Day gecko hatchlings generally reach sexual maturity at 6 to 12 months old.

Range and habitat

The Madagascar giant day gecko is native to tropical and subtropical forest in northern and northwestern Madagascar, where it is widely distributed. Day geckos in general live mostly in trees, including coconut palms and banana trees, and are also found near people, on fences, houses, huts and in gardens.

The species has also spread far beyond Madagascar. There are a few recorded populations in Florida and Hawaii. It was introduced to Réunion Island in the mid-1990s and is established on Mauritius, first mainly in the north of the island and later in Floréal and the upper Plaines Wilhems area. On Mauritius it has spread so widely that it is considered a threat to native wildlife. It competes for habitat with the island's own day geckos, including the blue-tailed day gecko, the lowland forest day gecko, the ornate day gecko and the upland forest day gecko.

Conservation status

The Madagascar giant day gecko is listed as Least Concern on the IUCN Red List. It is widespread in its home range and has established populations on several other islands.

The wider picture for day geckos is mixed. Some Phelsuma species are common and some are seriously endangered, and two species from the island of Rodrigues, including the Rodrigues giant day gecko, are extinct, probably because human settlers and their animals destroyed their habitat. Every Phelsuma species is listed on CITES Appendix II, which regulates international trade. Little is known about the trade in day geckos, but it is considered a threat to some species. The giant day gecko itself is bred and sold as an exotic pet.

Where it has been introduced, the giant day gecko is itself the conservation problem: on Mauritius it now encroaches on the habitat of four native day gecko species.