Spiny-tailed Monitor Varanus acanthurus

The spiny-tailed monitor, also known as the ridge-tailed monitor or spiny-tailed "goanna," exists in a number of sizes and colors throughout northwestern Australia. The spikes ring the tail, directed backward from the body, making it difficult to pull the monitor from a rocky crevice where it may be hiding. The tail is also useful in hunting, as the lizard can whip it around as a large, spiky club to attack prey. Though this species can be highly variable in color and pattern, red and yellow are the two distinct forms. Here at the National Aquarium, visitors can see the red phase spiny-tailed monitor, noted by its distinct brick-red color accented with dark and cream ringed spots. Spiny-tailed monitors are carnivores with a voracious appetite. Juveniles in the wild feed on insects, while adults feed primarily on smaller reptiles and mammals. We offer our monitors a variety of insects and small rodents weekly, allowing guests the opportunity to observe their feeding behavior. The maximum length of the spiny-tailed monitor is approximately 2 feet, although size varies with region. The spiny-tailed monitor is native to the northwestern part of Australia, in habitats ranging from tropical escarpment to red sand deserts. The spiny-tailed monitor is common within its range. Raptors, snakes and other monitors all prey on the spiny-tailed monitor, consuming adults, juveniles and eggs. The spiny-tailed monitor (Varanus acanthurus) or ridge-tailed monitor or Ackies dwarf monitor is an Australian species of lizard belonging to the genus of monitor lizards (Varanus). The spiny-tailed monitor, a medium-sized monitor lizard, can attain a total length of up to 70 cm. The tail is about 1.3-2.3 times longer than head and body. The upper side is a rich, dark brown and painted with bright-yellowish to cream spots, which often enclose a few dark scales. Its tail is round in section and features very spinose scales. There are 70-115 scales around the middle of the body. The spiny-tailed monitor is distinguished from the similar-looking species V. baritji and V. primordius by the presence of pale longitudinal stripes on the neck. This arid-adapted lizard is found in northern Western Australia, in the Northern Territory and in the eastern and northeastern parts of Queensland. The spiny-tailed monitor inhabits is associated with arid rocky ranges and outcrops. The spiny-tailed monitor is part of an exclusively Australian radiation of small monitor lizards, the subgenus Odatria. In the past, three subspecies of V. acanthurus were recognised: The continental subspecies V. a. acanthurus and V. a. brachyurus, and V. insulanicus, that only inhabits Groote Eylandt and the islands of the Wessel group. In 2006, the results of a study on the mtDNA of Australian monitors were published, according to which the two continental subspecies do not form natural (monophyletic), taxonomic entities. V. a. insulanicus was proven to be monophyletic, but it is more closely related to V. baritji than to other V. acanthurus. Therefore V. a. insulanicus might represent a distinct species. Wilson and Swan (2010) still accept V. a. insulanicus as a valid subspecies of V. acanthurus, which is easily distinguished from other spiny-tailed monitors by its dark colouration and more-banded pattern. Spiny-tailed monitors are diurnal, solitary ground-dwellers. This species is most often found in its shelter, mainly under rock slabs, boulders or in rock crevices. Only rarely do they hide in spinifex. As the spiny-tailed monitor has a lower level of activity compared to other monitor lizards, as well as a lower metabolic rate, it is often found in its hideout at day, and most likely it is a sit-and-wait-predator. They prey mainly on insects, especially orthopterans, beetles and cockroaches, and on small lizards such as skinks, geckoes or small dragon lizards. Less often, this species feeds on other insects, spiders, snails or young marsupials. Approximately 70% of its water requirement comes from food. In captivity, a clutch consists of up to 18 eggs. The young hatch after three to five months of incubation, and measure 15 cm. The knowledge on reproduction in the wild is sparse. Males most likely mature at 12 cm snout-vent length, females mature at 10–14 cm snout-vent length. Ovulation occurs in August and November. The eggs are deposited in self-dug tunnels.