Breeding Blue-Tongued Skinks

The short version

• Blue tongues give birth to live young. There are no eggs and no incubator [26][22].
• Sexing adults is hard. Seminal plugs, a seen hemipenis, pairing behavior or vet imaging are the only reliable signs [3][25][24].
• Australian forms need a real winter cool-down to breed. Indonesians do not, and should never drop below 70°F (21°C) [17][23].
• Pairings are rough. Supervise every session and separate the pair at the first sign of serious injury [28][18].
• Gestation is about 100 days. A Northern can have 10 to 20 babies in an afternoon [17][22][27].
• Every baby needs its own tub from day one. Siblings bite off each other's toes and tails within hours [18][17].

Before you start

The whole challenge with blue tongues sits in three places: knowing which animal is really male, getting a pairing done without the female being hurt, and having a separate tub ready for every single baby on the day they arrive. A single Northern female can drop 10 to 20 fully formed lizards in an afternoon, and they will chew each other's toes and tails by nightfall if left together.

Which skinks breed how

Two groups come through the US hobby, and they breed differently.

Northerns are the easiest Australian form to find in the US and the one almost every US breeder works with [2]. Indonesian forms are still exported, so wild-caught adults are common and locality labels are often unreliable (see chapter 7) [23][2].

Sexing: the honest answer is "hard"

Blue tongues have no external sex organs you can see, and head size, tail-base thickness and eye color all overlap between the sexes. LafeberVet puts it plainly: sex is "often difficult or impossible to determine" [3]. Before about two years of age, most keepers cannot sex them at all without a vet [17][23].

What does not work reliably

• Head and tail shape. A big triangular head and fat tail base are said to mean male, but a large female carrying fat looks exactly the same [25][3].
• Eye color. Males are more likely to have red-orange eyes and females yellow, but red-eyed females and yellow-eyed males are both reported, so use it only alongside other clues [17][23].
• Measurements and ratios. A 2022 study of 20 known-sex Eastern blue tongues found measurement-based sexing was only 35% accurate using published cut-offs, and 70% after the authors adjusted the ratios [24].

What does work

• Seminal plugs. Adult males drop small, paired, tadpole-shaped waxy plugs, often found on the floor or in the water dish. Crumbly white urates are not plugs. Plugs mean male [17][25].
• A hemipenis seen naturally. Some males evert their hemipenes while defecating or when startled. Seen once, you have a male [25]. Never try to force it by squeezing or "popping." It risks injury, and there is no safe home technique for an adult skink [17].
• Probing. Males do have hemipenal pockets, but blue tongues are thick-tailed, muscular and strong, and there is no published probe-depth table for the genus. Breeder experience is that probing is not a standard method for this group. Leave it to a reptile vet.
• Behavior. When two adults are put together under supervision, the one that chases, chin-rubs and tries to mount is the male [25]. Two males will fight, so be ready to separate them in seconds.
• Veterinary imaging. Contrast X-rays of the hemipenes under sedation were 100% accurate in the 2022 study [24]. MRI is also reliable but harder to arrange [17][23]. Ultrasound of adult females in season can also show follicles or embryos. This is the route for an animal you need to be sure about.

Maturity and condition

• Age. Most reach sexual maturity at 2 to 3 years [3]. Field data for T. scincoides puts it at about 561 to 590 days (roughly 1.5 to 2 years), with females maturing at about 9 to 14 in (24 to 36 cm) snout-to-vent depending on the population [22]. The Blotched blue tongue is slower, maturing at 4 to 5 years [26].
• Size and weight. Breeder experience, not proven: wait until a female's third spring, and only pair her if she is at full adult length and solid weight. A Northern female is typically well over 500 g, often 700 to 900 g; an Indonesian female 400 g or more. Litter size goes up with female age and size, so an early first litter is both smaller and harder on her [22].
• Health check first. Get a fecal exam (critical for any wild-caught Indonesian), and make sure she has a good UVB and calcium history, no stuck shed on the toes, and no obesity. Bone disease and obesity are the two most common husbandry diseases in this species, and a pregnant female with low calcium stores is at risk [3][20].
• Males. One healthy adult male can breed several females in a season. Males breed every year; females of some species likely do not [26].

Brumation and semi-brumation

In the wild, T. scincoides mates August to October (the Australian spring) and gives birth December to February [22]. In the US, captive Northerns are usually cycled through our winter so that pairings happen in late winter or spring.

Australian forms (Northern, Eastern, Blotched, Western)

Note that the brumation schedule above comes from a hobby article, not a veterinary source [18].

Indonesian forms (T. gigas and Tanimbar)

Brumation is not required for T. gigas to breed [17][23]. Many breeders still "semi-brumate": drop the basking spot 5 to 10°F (3 to 6°C) and shorten the day a little for a few weeks [18]. Never let Indonesians fall below 70°F (21°C) [17][23]. They come from humid equatorial islands and can develop respiratory problems if chilled.

Introductions and courtship

Blue tongue mating is rough to watch. The male chases, chin-rubs, then bites the female's neck, flanks or back to hold on. Scale damage and light bleeding are common and considered normal [17][27][18]. The female pushes back and may fight if she is not ready [28]. The real danger is a male that rolls or thrashes while biting a limb: a leg can be badly torn or lost [28], and deep bite wounds on the female's body are a reason to stop immediately [18].

How breeders run a pairing (hobby reports [28][18]):

1. Keep the sexes in separate enclosures all year. Introduce the male into the female's enclosure, or use a neutral tub with a towel for grip and no loose bedding, so you can see and reach them [28].
2. Watch the whole session, 30 to 60 minutes [18]. Never leave a pair together unsupervised [28].
3. Look for a receptive female: she stands still, lifts or wiggles her tail, and may raise her tail when her back is scratched. Mating follows when the male strokes her tail with a hind leg and she lifts it. Keeper reports put mating at anywhere from a few minutes to over an hour; this is keeper experience, not proven.
4. Separate them when they are done, or the moment either one starts rolling, thrashing its tail, biting feet or toes, or causing open wounds [17][18].
5. The female stays receptive for about a month. Pair three or four times across that window, a few days apart, then stop [17][23]. A male that shows no interest after 4 or 5 tries probably needs more cooling or more recovery time [18].
6. Clean bite marks with a dilute antiseptic wash and watch for infection. Anything deeper than scale damage needs a vet.

Gestation and live birth

Blue tongues are viviparous. Embryos develop inside the female, fed by a large yolk and a well-developed placenta, and the babies are born fully formed [26].

• Length. About 100 days is the working figure breeders use for both Northerns and T. gigas [17][23][27]. Field estimates for T. scincoides run 3 to 4 months [22], and some keepers report 3 to 5 months depending on the female [18]. Count from the last successful mating and expect anywhere from 90 to 150 days.
• Caring for the pregnant female. Keep normal heat and UVB; she will bask hard. Feed her well early, and expect her appetite to drop in the last few weeks as the babies take up room. Offer calcium with every meal. Handle her as little as possible in the final month.
• Birth. A litter is born over about 1.5 to 8 hours [22]. Each baby arrives in a membrane, breaks free on its own, and often eats its placental membrane [26]. One or two stillborn or undeveloped "slugs" in a litter of 15 is normal, according to a hobby report [18].

Litter sizes

For planning tubs, expect roughly 5 to 15 for a Northern and 5 to 25 for Indonesians. Plan for the top of the range.

Neonate care and first meals

Size at birth. T. scincoides babies measure about 3.5 to 5 in (9 to 13 cm) snout-to-vent, roughly 5 to 6 in (13 to 15 cm) total, and weigh 8 to 21 grams [22][18]. Indonesian babies are smaller.

One baby, one tub, from day one. This rule is not negotiable. Siblings bite each other's tails and toes within hours, and the damage is permanent [18]. Babies are fully independent at birth and should go into their own enclosures as soon as possible [17].

A simple setup per baby (keeper experience, not proven; the hobby report says only that each baby needs its own enclosure [18]):

• a 6 qt (6 L) shoebox tub for the first two months, then a 12 to 15 qt (12 to 15 L) tub
• paper towel substrate and a small water dish
• a warm spot of about 90 to 95°F (32 to 35°C) under a lamp or over heat tape, always on a thermostat
• a cool side of 75 to 80°F (24 to 27°C)
• UVB over the tubs if you can arrange it

First shed and first meal. Babies shed for the first time within a few days of birth [26] and usually eat in the first week; wild babies start on small insects and fruit within days [27]. Offer food from day 2 or 3: a soft omnivore mix (high-quality wet dog food or a reptile omnivore gel, plus finely chopped greens and fruit) dusted with calcium, with a few small dubia roaches or chopped mealworms for movement. Feed daily at first, then every other day once they are eating well. Remove uneaten food within a few hours.

Growth. Well-fed juveniles grow fast and can approach adult size in about a year. Adult color and gloss appear at 8 to 9 months [22]. Juveniles bask hotter and more often than adults, so give them a real basking spot even in a tub setup [22].

Never group-house babies. Blue tongues are solitary and territorial (the Shingleback is the only social species) [2]. Housing juveniles together to save space leads to lost toes and tails.

How often a female can breed

• One litter a year is the biological limit. The breeding season happens once a year [22][27]; there is no double-clutching as with geckos or dragons.
• Every other year is kinder. Pregnancy is a heavy drain. The Blotched blue tongue is believed to breed only every other year in the wild for this reason [26], and at least one hobby source recommends breeding captive females every other year at most [18]. Breeder experience, not proven: many US Northern breeders do breed good females every year, but they skip any female that comes out of a litter thin or is slow to regain weight.

Realistic planning numbers:

When babies are ready for new homes

This is breeder experience, matching what established US breeders post in their terms of sale:

• Minimum: after the first shed and at least 5 to 6 steady meals, which in practice means 3 to 4 weeks old. A baby should never go home before it has eaten several times on its own.
• Better: 6 to 8 weeks, at 25 to 40 grams for a Northern. By then weak feeders have shown themselves, and the baby handles travel and a new enclosure with less stress.
• Keep records: birth date, litter ID, parents, locality or morph, weights every 2 weeks, and a shed and feeding log. Buyers of Indonesian localities and of genetic morphs will ask for lineage [17].
• Sell as unsexed. Babies cannot be sexed (see above). Do not guess.
• Send a care sheet with every baby, including the rule that blue tongues must be housed alone.

Quick reference