Blue or False?
Identifying and caring for Indonesian blue-tongue skinks.
Blue-tongue skinks have been popular pets for decades. Seven separate species make up the Tiliqua genus, which includes the shingleback lizards (T. rugosa) and the pygmy blue-tongue (T. adelaidensis) of Australia. However, this genus is most characterised by the bulky, smooth-skinned and charismatic blue-tongue skinks of Australia and Indonesia. Historically, Australian blue-tongue varieties were very popular and morph breeding in the US opened an entire subculture of keepers dedicating their time to producing these impressive animals. Now, our data shows that the most dominant pet species in the UK is now T. gigas, commonly known as the Indonesian or “giant” blue-tongue skink. This species inhabits the tropical forests of Indonesia, Papua New Guinea and the surrounding islands. Not only are these animals different to their Aussie cousins, but speciation has led to three distinct subspecies, with several ‘locales’ regularly exported over the last 40+ years. Over that time, crossbreeding between locales has likely happened, but a better understanding of the distinctions between each population will undoubtedly improve the husbandry of these loveable lizards.
The iconic blue tongue is vibrant in most individuals
Indonesian blue-tongue skink
Tiliqua gigas gigas is the nominate form of this species. However, due to its distribution, island ‘locales’ have evolved in isolation from one another for millions of years. This means that although the Indonesian blue tongue skink is a distinct species, further studies into each population have described several subspecies. There are bound to be more identified as taxonomists continue to study these populations, but for now, these unique animals are referred to as ‘locales’. Some of these locales are already widely available in captivity and are as follows…
Halmahera: The Halmahera blue tongue skink is a subspecies of T. gigas that is found only on the Halmahera Island in North Indonesia. Distinguishable by their red/grey colouration and thin dark markings as well as a different scale structure around the eye, this is a unique variation on the nominate form. Caring for Halmahera blue-tongues should be identical to other island forms of T. gigas. Although many animals with black banding are listed as ‘Halmahera’ regardless of their lineage, in the wild this species would be exposed to the highest levels of humidity of any blue tongue species. Keepers should average around 70% RH, with daily spikes up to 100%. This contrasts with other T. gigas found on more southernly islands which tend to thrive at 50% with spikes of 80% humidity.
Irian Jaya: Irian Jaya is the name given to the Indonesian (Western) side of Papua and adjacent islands. It is a huge landmass with a vast spectrum of biotopes and climates. Although the ‘Irian Jaya’ blue-tongue is taxonomically incomplete, it is widely believed this species thrives in lower-humidity environments when compared to other island forms. They are variable in their patterning and not always easy to distinguish from other subspecies or locales. This has led some people to believe it is a cross between the Tiliqua gigas species of Indonesia and the Tiliqua scincoides (Eastern) species of Australia, from when there was a land bridge between the two countries.
Tiliqua gigas gigas
Kei island blue-tongue skink
Tiliqua gigas keiensis
The ‘Kei Island’ blue tongue originates (unsurprisingly) from the Kei Islands of Maluku in Indonesia and perhaps the neighbouring Aru Islands. These islands are part of Wallacea and sit at a Northernly position in the blue-tongue skinks range, suggesting that high humidity and a tropical environment will provide optimal care. They are a very robust subspecies of T. gigas and are characterised by their orange base with speckled patterns that stretches from their head and down their torso. Juveniles will develop these patterns at around 3-6 months of age. Their unique appearance prompted the distinction of this subspecies back in 1894 and since then the islands changed their name from “Key” to the colloquial “Kei” spelling, with the scientific name ‘keyensis’ following suit. They are reported to be one of the more aggressive subspecies of blue-tongue though this could be because most of the animals in the hobby are wild-caught. Captive breeding of this species has been successful in the US, but as blue-tongues are not prolific breeders, they are still reasonably rare in the UK and Europe.
Tiliqua gigas keiensis
The faded blue-tongue skink
Tiliqua gigas merauke
Pronounced mer-oo-kee, T. g. Merauke (sometimes referred to as the ‘faded’ blue-tongue) is the longest subspecies of the Indonesian blue-tongue skinks. They inhabit transitional coastal plains of Irian Jaya, suggesting they require a reasonably low humidity (around 60%) and may benefit from drier elements in the composition of their substrate. These huge lizards can reach up to 70cm in length and often have extremely good temperaments, making them one of the more popular subspecies available. They are routinely captive-bred across the world. However, these animals may not be true Merauke’s as this species shares its distribution with other locales of the nominate form and can be extremely variable in colour. In fact, the concept of a ‘true Merauke’ is hotly contested across herpetologist circles, with many researchers believing this is just another colour form of the Indonesian blue tongue, T. gigas.
Tiliqua gigas merauke
The ‘other’ blue-tongues
There are several other species of blue-tongue found across Australia which have their own subspecies, colour morphs and locales. The Eastern (Tiliqua scincoides) and Northern (T. s. intermedia) blue-tongues are most commonly seen in the pet industry, but due to export restrictions are generally less widespread in the hobby than their Indonesian counterparts. However, there is one subspecies of the Eastern blue-tongue which inhabits the Tanimbar Islands of Maluku, Indonesia. Tiliqua scincoides chimaerea, the Tanimbar blue-tongue skink has an incredibly glossy appearance, small body and fierce attitude. Tanimbars have very firm bodies compared with other blue-tongue species with faded streaks down their back. Their name comes from Chimera, a mythical fire-breathing dragon. Herpetologists are still unsure why the blue-tongues on this island have evolved such firm bodies and feisty attitudes, predicting that there may be a specific predator or higher density of predators on the island that this species needs to contend with.
Keepers should be extremely vigilant in understanding exactly what species of blue-tongue skink they are caring for. Although these animals are not readily available in the UK, the blotched alpine locality of the Eastern blue-tongue (Tiliqua scincoides) can tolerate extremely cold conditions and inhabit areas that are frequented by snow. The Central blue-tongue, on the other hand, thrives in the heart of Australia where temperatures can reach upwards of 40°C. As these are completely distinct species (as opposed to the subspecies and island localities of T. gigas), they are easily distinguishable. It would be very difficult for someone to source a Centralian blue-tongue for a similar price as a ‘Northern’. Yet, it would not be out of the realms of possibility for an animal to be rehomed under the ‘blue-tongue’ banner and a novice keeper to believe all species are synonymous. Naturally, these specialist species require entirely different environmental parameters to T. gigas sp.
Tiliqua scincoides
Indonesian blue-tongue care
Blue-tongue skinks often have docile personalities and have made excellent pets for decades now. They are routinely bred in captivity but continue to be imported from the wild in small numbers, which supports bloodlines with sturdy genetics and healthy animals. As females are viviparous and produce just a few large, stocky offspring once a year, the availability of this species can be sporadic. It has also meant that prices for T. gigas have risen sharply in the last 10/15 years now their appeal as pets have become well-established.
Another appeal of this species in captivity is its omnivorous feeding habits. Juveniles will tend to eat a larger ratio of meat to vegetables, but this should even out to around 50:50 as the animal reaches sexual maturity around two years old. Dedicated ‘blue-tongue’ diets exist, but eggs, rodents, mince/dog food and a wide variety of insects can be used. Blue-tongues are known for enjoying soft-bodied prey, but keepers should be wary that they can become picky-feeders if they are constantly fed a single, rich food source.
Sally Fairclough, Experienced Zookeeper and Head of the Animal Team at Peregrine Livefoods said: “Blue-tongues require an extremely varied diet. When we have young blue-tongues in, we’ve given them a brilliant high-energy diet to ensure they’re fit and healthy before they’re sold on. This consists usually of raw or scrambled eggs, with crushed crickets and locusts and some berries too. We’ve also found that they love Repashy Blue-tongue Buffet and this tends to support their health over time too. We also frequently provide snails, which they love! People often make the mistake of just throwing a few crickets into a blue-tongue enclosure and that doesn’t work long-term. They need a varied diet, this is extremely important to them.”
Blue-tongues, like all other reptiles and amphibians, should have access to UV but their cryptic behaviours can make this difficult to assess. They are diurnal and hail from the tropics suggesting they need high UVI, but they are also terrestrial, living amongst high grasses or the forest floor and probably receive much lower exposure than other animals in the same biotope. Some island forms will inhabit coastal plains (mimicking the grassland environments of their Australian cousins), while others will thrive in dense rainforest. Although Tiliqua scincoides is considered a Ferguson Zone 2-3 animal, T. gigas is yet to be officially categorised. Applying this logic, whilst also providing plenty of hides and foliage would be recommended.
Although blue tongue skinks are typically slow-moving lizards, they are very large and demand a good amount of space. Similarly-sized lizards such as bearded dragons (Pogona vitticeps) will perch and climb, which allows the keeper to create a three-dimensional enclosure that utilises all available space. This is not possible for ground-dwelling species. In fact, whilst many people would argue that terrestrial animals are easier to house, this can be another challenge that the keeper must consider. They should not be housed in anything shorter than five feet in length, with six feet being more appropriate. Height is less of an issue, but installing light fixtures may be easier in a taller vivarium and will make room for various hides and artificial or growing plants.
Breeding blue-tongues
Blue-tongue skinks are routinely bred by many hobbyists and lots of pet shops will keep a breeding pair as they are usually quite straightforward to breed. However, there are a few notable challenges when embarking on a blue tongue breeding project. Firstly, sexing blue tongue skinks is incredibly difficult. In fact, before the age of around two years old, all species and subspecies are practically impossible to sex without veterinary intervention. Northern blue tongue skinks (T. scincoides) can sometimes be sexed based on their head size and bone structure as they get older. However, the breeder would need to select from a good number of animals to create a ‘best guess’ as a straight comparison between two animals is unlikely to be conclusive. Unfortunately, this method of identification does not work with Indonesian subspecies as both males and females can differ greatly in size and shape.
One method of sexing that applies to all species, including the Indonesian varieties is by identifying the colour of the iris. Males are more likely to have red irises, whereas females are more likely to have yellow irises. This is completely unreliable, as there are many reports of females with red irises and males with yellow. However, it can be used in conjunction with other identifiers to help the breeder make an informed guess.
James Wilson is an expert blue-tongue breeder in the USA. Writing to blue-tongueskinks.org he claims: “The presence of, or lack of, seminal plugs has proven to be one of the most reliable indicators that I have used in determining the sex of my blue-tongued skinks. Most hobbyists overlook this dead giveaway because they keep their skinks on dirt, bark, gravel, or aspen bedding. The seminal plugs simply get lost in the substrate, never to be discovered by the skink's owner. I have found that when I keep my skinks on artificial turf, at least during brumation and the breeding season, the males will "drop" seminal plugs daily. These plugs are small (about the size of a bb) clearish-white slimy little blobs with tails that give them a total length of about 1-inch. They resemble small tadpoles and are usually found in pairs. They are quite obvious on the turf but will dry up by the end of the day, turning a yellow-brown colour and withering into thin brittle twigs. At this point, they are very easy to mistake for a small piece of aspen bedding or a dried up piece of cut grass. Some people confuse seminal plugs with the urates that skinks produce along with their faeces. Urates are the white chalky portion of a skinks waste matter. During brumation, they are produced in the absence of faecal matter, because the skink has not taken in any food, but was still given access to water. This can be misleading, and it is important to know exactly what you are observing. Remember that urates are chalky, and they will crumble up quite easily in your fingers, while seminal plugs come in pairs and look like very small albino tadpoles.”
There are other, more invasive methods of sexing blue tongues. Some breeders will expose their animals’ hemipenes but this can risk damage and future health complications. Finally, an MRI scan will sex a blue-tongue skink with confidence. For breeders dealing with many animals or high-end morphs, this might be a worthwhile investment. For most hobbyists, however, it is a very expensive procedure that is often unviable.
Brumation should be encouraged in Australian species, but it is much less important for Indonesian subspecies. All T. gigas species experience a ‘wet’ and a ‘dry’ season in the wild and therefore do not require a brumation period to breed. This being said, many hobbyists will choose to semi-brumate their animals in anticipation of breeding. Dropping temperatures just a little bit and reducing the photoperiod will mimic wild seasonality. The animals will lose their appetite and become less active. Keepers of gigas sp. should not drop temperatures below 21°C (as opposed to the Australian subspecies which will happily tolerate 15°C for several months). Not all blue tongue skinks will want to brumate. Even those that experience the harshest conditions in the wild might find that their captive environment does not warrant the need to brumate. Therefore, the keeper should be extra vigilant around winter and observe their animals’ behaviour. If the animal is becoming extremely inactive, brumation is encouraged. If the animal is simply reducing the amount of food they eat during winter, this is perfectly normal and does not necessitate drastic temperature drops.
Once both animals are receptive (females will reportedly react to a little back scratch by raising or wiggling her tail, whilst males are noticeably more active), pairing can commence. The breeding process is anything but romantic. It can be very daunting for a new breeder to watch their animal's mate. Males will be very aggressive and bite the flanks of the female. She will also be pushing back, testing the male’s strength, in what can appear to be a rather vicious struggle. Although males can be introduced to a female’s enclosure, using a separate tub will allow the keeper to observe the process and break up the wrestling if, for example, the male begins biting the females’ feet and toes. Eventually, he will stroke the top of the female’s tail with his hind legs and, if he is successful, she will lift her tail and allow him to copulate. If they are unsuccessful, they should be separated and paired again a few days later. The female will be receptive for around one month and should not be paired with males more than 3-4 times during this period.
Blue-tongue skinks will generally give birth to between five and 15 young after a gestation period of around 100 days. The young are fully formed, independent lizards that should be introduced to their new enclosures as soon as possible.
Baby blue tongue skinks
The importance of reputable breeders
Anyone who is looking to source an animal should have a keen desire to know where that animal came from. With many shops breeding their own blue-tongue skinks, a few simple questions about the lineage of the animal should help the keeper identify the exact species/locale. Networking with breeders who produce specific varieties is also a great way of picking up unique tips for that locale/subspecies. Hardy species that have occupied herpetoculture for decades often make excellent pets. Sometimes, however, it is the longest-kept species that require the most effort and research to update their husbandry practices.
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