Difficulty: Intermediate
Published: February 27, 2021
Updated: May 26, 2022
The ackie (also known as ridgetail(ed) monitor, spiny-tailed monitor, or ackies dwarf monitor) is a diurnal, terrestrial monitor lizard native to the west, north, and center of northern Australia, including some islands off the northern coast. They prefer arid and seasonally dry habitats with lots of rocks, boulders, and spinifex grass, and often shelter in crevices between the rocks as well as burrows underneath them.
Ackie monitors are long, slender monitors with a snakelike tongue, sharply tapered snout, somewhat rounded body, relatively short legs, and a whiplike tail. The body is typically red, brown, or black-brown with yellow, cream, or red spotting. The head typically features three pale stripes running from the face to the neck. The tail is long and covered in heavily keeled scales in a pattern of alternating light and dark rings, giving it a spiny appearance and function. The underside is typically pale and patternless.
Photos contributed by Brian Bush on Flickr.
As a dwarf monitor under the subgenus Odatria, ackies are fairly small even as fully-grown adults: sources generally agree that adult ackies are typically around 2’/0.6m long, but they have been reported as small as 17.3”/44cm and as large as 30”/76cm. Males are typically somewhat larger than females. It is reported that red ackies generally grow larger and have relatively longer tails than other localities (Kuhn & Julander, 1999). Ackies in general are known to live for at least 15 years with good care.
There are three subspecies of Ackie Monitor:
It is our belief here at ReptiFiles that reptiles are more complex than they have been long assumed to be, and no species can be appropriately described as simple or stupid. However, monitor lizards are well known to be especially complex and intelligent among reptiles. They have mammal-like features in their physiology (Horn & Visser, 2007), and have demonstrated exceptional intelligence even in captivity. Although some reptile species will tolerate minimalistic husbandry conditions, monitors will not. Keep this in mind as you consider the ackie monitor as a pet.
Special thanks to John Aromando, Jeff Easter, Steven Bowman, David Archer, Linnea Saphia, and Stefan Windsor for their contributions to this guide.
Map credit: Nrg800, CC BY-SA 3.0, via Wikimedia Commons, altered from original