The Madagascar giant day gecko is more colorful and full of spots than any other gecko.
This lizard typically reaches a total length of about a foot, though larger specimens have been found. The body color is bright green or, rarely, bluish green. A red stripe extends from the nostril to the eye. On the back there are red colored dots or bars. These red markings are quite variable, and in some cases, completely absent, though the line extending from the nostril to the eye is always present. Some specimens may have small blue spots. Young individuals of the species often exhibit much more red than their parents, but as time passes, many of the markings fade, to leave those that will remain until the gecko dies. The underside of these animals is a creamy white ranging to an eggy yellow. A stressed animal is more likely to have darker coloration, making it appear as though there are orange parts to the red coloration, and the green appears far darker.
This species is widely distributed in northern and northwest Madagascar. It can also be found on some of the off shore islets. There are a few recorded populations of this species also in Florida, and Hawaii, introduced by accident, which seem to like the climate in these locations. Phelsuma grandis is often found on different trees where it can be seen basking. They also inhabit human dwellings due to the number of appropriate basking spots, and the level of insect activity which these dwellings attract. Their normal climate is rather dry, though heavy rainfalls are quite common. This means that there is a constant level of high humidity throughout the year.
These day geckos feed on various insects and other invertebrates, and occasionally have been recorded consuming small vertebrates. They also like to lick soft, sweet fruit, pollen and nectar. In captivity, these animals can be fed with crickets, wax moths, fruit flies, mealworms and houseflies.
Giant day geckos may move slowly but, if frightened, are very fast, agile, and are adept at escaping. Like most Phelsuma species, the males can be quite quarrelsome and territorial and will not accept other males in their neighborhood. The females lay up to 6 pairs of eggs. The young will hatch after approximately 60–65 days. When the babies are about two years old they will leave their mother and find a mate or a new home.
Madagascar giant day geckos are not considered endangered.
The 60-plus species of day geckos are residents of Madagascar, the Comoro, Andaman and other Indian Ocean Islands and eastern Africa. Giant day geckos are very fast, and many have escaped from dealers to become established in the Miami area, as well as on the Hawaiian Islands. Longevity can exceed 10 years, and may near 20.