Varanus acanthurus brachyurus is known as the ackie monitor based on its scientific name, or the spiny-tailed monitor due to its spiky tail. Ackie monitors come in two subspecies, yellow (V. a. brachyurus) and red (V. a. acanthurus). As their name suggests, the two differ in coloration, and yellow ackies also tend to have a shorter tail.
Yellow ackie monitors exhibit a brown to dark golden background color, covered with ocellated spots that range from cream, yellow, or yellow-orange in color.
Despite being on the smaller side compared to other monitors, this species still gets sizable and is very active, therefore requiring a considerable amount of space. Hatchlings and juveniles can be housed in a 20-30 gallon (or a 24x18x18 enclosure), but they must be upgraded as they age. An adult or adult pair should be provided at least a 50-60 gallon terrarium, with larger groups requiring even more space. A variety of substrates will work, provided three key elements: it holds onto moisture fairly well, it’s good for digging/burrowing (i.e. holds it shape), and a deep layer (6-12 inches) is provided. Sand/soil or sand/coco fiber mixtures work particularly well, and other elements, such as cypress mulch or orchard bark, can also be mixed in. Provide hides under which the monitors can bury, especially underneath the basking spot; cork bark, stacked rocks, or similar items work well. Be sure that any heavy items are supported by the bottom of the enclosure and not the substrate, as these monitors will dig underneath cage decor. While a deep substrate is key, low climbing material in the form of branches, cork bark, and other decor can be provided.
Hatchling/juvenile ackie monitors can be housed in groups, but this must be done with caution: certain individuals may simply not get along and must be separated, or some individuals may either outgrow or be outcompeted by others. Ackie monitors that are raised together as early as possible tend to get along better than adults that are grouped together. Otherwise, when putting separately raised adults together, it is best to avoid putting same-sex individuals together that were separately raised. Regardless, animals put together should be kept under close observation for the first few days, and individuals should be separated as needed.
Ambient temperatures for ackie monitors should remain between 75-85 F. A hot basking spot is paramount for this species; use a basking bulb to provide a basking spot of at least 120 F, although basking temperatures between 140-160 F are ideal. The necessity of UVB light for monitors, despite being a diurnal species, is debated, but we do prefer to provide it for our monitors. Mercury vapor bulbs are a good choice for providing ample heat along with UVB lighting. Temperature should be monitored with a digital thermometer, and the basking spot can be checked with an infrared thermometer or temperature gun. Night temperatures can safely drop down to 70 F.
Although ackie monitors live in arid regions, they spend a lot of their time in humid microclimates. Ideal ambient humidity in the enclosure is higher than other arid species at around 50-65%, but can remain around 40-50% provided humid microclimates are accessible (i.e. deep substrate). A humid hide can be provided, but the best humid hide is to provide deep burrowing substrate. It is not recommended to sacrifice ventilation to increase humidity within the enclosure. Ackie monitors should be misted around three to four times a week to raise humidity and moisten the substrate. A water dish is recommended, but will not take away the need for regular misting.
Ackie monitor hatchlings are around 2.5-3 inches long. Adults will reach a total length between 2 and 2.5 feet.
Ackie monitors are carnivores and should be provided a varied diet consisting primarily of feeder insects and invertebrates, with occasional whole prey items such as small rodents. Appropriately sized dubia roaches, crickets, superworms, and hornworms make for an excellent staple diet. Smaller prey items, like mealworms or the occasional waxworm/butterworm as a treat, can be offered to juveniles but may be ignored by larger individuals. Feeder insects should be gut loaded and dusted with a vitamin/mineral supplement.
Ackie monitors are difficult to sex. Both species exhibit enlarged scales beneath the vent, although these appear larger in males. Males tend to have a thicker neck and wider head as well. Adult females housed with males may exhibit minor wounds and scarring around the base of the head and neck from breeding behavior.
Ackie monitors will typically breed through the spring and summer months, providing up to 6 clutches per year, with clutch sizes ranging anywhere from 6-18 eggs. Brumation is not always necessary but will help cycle these monitors.
Reptiles Magazine - an excellent and detailed look at ackie monitor natural history, care, and breeding