by John Clare
|Family:||Ranidae (True Frogs)|
| Origin: ||Sub-Saharan Africa (Angola, Botswana, DR Congo, Kenya, Malawi, Mozambique, Namibia, South Africa, Tanzania, Zambia, Zimbabwe). Due to a number of similar species/subspecies, the frog we associate with "Giant African Bullfrog" is likely confined to South Africa and neighboring countries.|
|IUCN (Red List) Status:||Least Concern (LC)|
|CITES Status:||No Listing|
|Adult Snouth-to-Vent Length:||Male: 11.5-25 cm (4.5-10 inches); Female: 9.0-14 cm (3.5-5.5 inches)|
|Lifespan:||15-25 years in captivity|
|Activity:||Minimal, except during feeding - more active than "Pacman" Frogs|
| Temperature: ||Day: 25-32 °C (77-90 °F); Night: 20-25 °C (68-77 °F)|
|Food:||Insects, Earthworms (Nightcrawlers), Amphibians*, Rodents*, Lizards* (*feed thawed frozen, or lab-fed live animals to avoid parasites)|
|Call:||Hear the call of the Giant African Bullfrog|
Description & Life History
The Giant African Bullfrog, Pyxicephalus adspersus, is the second largest frog in the world, the largest being the Goliath Frog, Conraua goliath. Vendors in the pet trade often use distortions of the African Bullfrog's scientific name, such as "pixie frog" and "pyxie", to refer to the young froglets that often surprise new pet owners by growing into monsters. Adult males can weigh well over a kilo (over 2.2 lbs) and males typically reach a snout-to-vent length of 17.5 cm (7 inches); specimens over 20 cm (8 inches) have been recorded (Passmore and Carruthers). Females rarely exceed 12.5 cm (5 inches). Most anurans exhibit sexual dimorphism in size, generally the female being larger than the male. The African Bullfrog exhibits extreme size differences between the sexes, but the male is the larger animal. Males also have more powerful limbs and larger skulls. In the wild, some larger male African Bullfrogs in a population will demonstrate parental care by guarding their tadpoles against predators and, when necessary, insuring sufficient water is accessible to their brood by digging channels between pools (Balinsky and Balinsky; Kok and Du Preez; Cook, Ferguson and Telford). These guardian males have been known to attack animals much larger than themselves in defense of their offspring. The size differences between the sexes are probably due to this parental behavior and the violent fighting that occurs between males at breeding time. Fighting takes the form of grasping an opponent in an attempt to flip or throw him (Passmore and Carruthers). These frogs are equipped with bony tooth-like projections called odontoids, located in the center of the lower jaw, which can deliver a very painful and bloody bite to an opponent or the finger of a human being. When forced on the defensive, these frogs will puff up with air to appear as large as they can, and in the case of guardian males they will lunge at the attacker with jaws open in an attempt to deliver a discouraging bite.
Adult frogs are generally green to dark green above, and pale cream or white below, with grayish blotches/spots. The pupils are horizontal, and while the fingers lack webbing, the toes have fleshy webbing. Both sexes have deep orange markings where the limbs meet the body. Males tend to have a large amount of yellow coloration along the flanks and sometimes onto the throat; females have little yellow coloration beyond the base of the limbs. This bright coloration on males appears to play a display role during breeding (Channing, Du Preez and Passmore). Adult males have proportionally larger heads, particularly where the head meets the body. Sexing of these frogs is most difficult before their gonads develop but sex differences are usually quite apparent by a length of 10 cm (4 inches). If you hear an unsexed frog call like the sound clip above, it's 100% male. Both sexes may grunt or force air through their airways to produce a dull hiss when grasped around the midriff, but females do not call.
Metamorphs are distinctly different in appearance to adults (so much so that lay men frequently don't realize they are the same species). Metamorph froglets have black and various shades of green on their body, and three lines of bright green color, one running along the back from the nose to the vent, and one on either side of the body from the nose to the eye and from the eye along the side. These lines fade with age and this fading varies from individual to individual.
|Two wild male African Bullfrogs in Gauteng, near Johannesburg, South Africa. The male on the left shows just how large these frogs can |
grow. Photo ©2009 Darryn Rogers / FrogForum.net
|Adult male Pyxicephalus adspersus showing yellow coloration. |
Photo ©2008 John P. Clare / FrogForum.net
|Male (left) and female (right) P. adspersus. Note the difference in head shape and relative size, and note the relative lack of yellow coloration in the female. Females tend to retain the central stripe. |
Photo ©2008 John P. Clare / FrogForum.net
In countries where these frogs live, like South Africa, the climate is dry for much of the year. In Gauteng, South Africa, certainly the origin of most of the scientific studies of this species, the winter months of June, July and August see virtually no rain and temperatures are relatively cool (average temperatures for these 3 months: 5-17 °C/41-63 °F) (South African Weather Service). Significant rains are generally confined to the period of September to January and these wetter times correspond to the above ground activity of these frogs.
|This is a young male Dwarf African Bullfrog, Pyxicephalus edulis. This frog is rarely available in the pet trade - the vast majority of frogs sold under this name are not in fact this species. |
Photo ©2009 John P. Clare / FrogForum.net
African Bullfrogs can spend as much as 10 months of the year aestivating to conserve water and to wait out conditions of drought and extreme temperatures.1 This aestivation involves burrowing into soft earth using the frog's massive, flanged inner metatarsal tubercle (a projection found on each rear foot). When buried, the frog sheds many layers of skin which harden into a paper-like cocoon with only the frog's nostrils exposed. The frog enters into a state of low metabolic activity and water retention.
|Froglet of Pyxicephalus adspersus with a Euro coin and a US quarter for size comparison, and a juvenile female P. adspersus showing the contrasting colors often seen in juveniles. |
©2008 John P. Clare / FrogForum.net
Emergence is triggered by the first significant rains of summer, and breeding begins during the first daylight following the rains (if the rains occur at night, otherwise breeding activity is immediate). African bullfrogs are largely diurnal and this also applies to their breeding behavior. Adults congregate in ponds where the males call with a low, ~1 second long whoop that resonates in the region of 100-300 Hz, sometimes likened to the sound of a cow (the top part of this article contains a recording of a male Pyxicephalus adspersus calling). The call isn't very loud and it doesn't carry far. Males form groups; males fight and larger males may exclude the smaller males from the center of the group. Males assert dominance over others by lunging at, chasing and/or throwing their opponents, and the bites from these attacks can result in the death of smaller males and the loss of eyes. Females remain outside the group of males, at a distance, and when ready to breed they dive under the perimeter males to reach the central males. Amplexus, the grasping of the female behind the forearms by the male, occurs and the pair will spawn within a few hours in water approximately 7.5 cm (3 inches) deep. When ready to spawn, the pair lifts their hindquarters clear of the water and the female stimulates the male with her legs to trigger his release of sperm over her eggs. These are produced in midair and spread around the hindquarters to distribute the sperm, after which the eggs fall into the water. A total of 1600-4000 eggs are laid. The female signals her dismissal of the male by a prolonged arching of the back or by a tonic stretching of her body, whereupon the male releases his grasp and the pair separates. The male will attempt to breed with other females if possible but at this point the spawned female's role ends.
After the flurry of breeding ends, many males and all females leave the spawning area. Larger dominant males may remain with their eggs (it is not clear if all of the eggs they guard are their own, though it seems unlikely). The tadpoles hatch within 48 hours at about 29 °C (84 °F) (van Wyk and Kok) and they have been observed to form a swarm/school around the guardian male (if he is present) 24 hours later. The tadpoles are omnivorous and detritivorous (cf. the Horned Frogs/Pacman Frogs, Ceratophrys, of South America, whose tadpoles are carnivorous but whose adults are very similar in behavior and habit to African Bullfrogs). The male will guard the tadpoles against predation, and males may be killed by predators in the process of defending their tadpoles. It was once thought that males may also eat some of their tadpoles, but this seems unlikely. Tadpoles may reach a total length of 6.4 cm (2.5 inches) at metamorphosis, and this can occur in as little as 17 days at 29 °C (84 °F). Pre-metamorphic tadpoles already exhibit the dorsal ridges of metamorphosed frogs. Metamorph froglet size is in the region of 2.2-3.6 cm (0.87-1.4 inches).
Metamorphosis is followed by rapid growth because these frogs must build reserves in preparation for the next drought. One laboratory study that employed a modest diet showed that these frogs can reach ~11 cm (4.3 inches) for males and ~8.5 cm (3.3 inches) for females in under 200 days post-metamorphosis.9 Pet keepers have grown these frogs at even faster rates: for example, I have seen frogs grow as much as 3.5 cm (1.4 inches) in 30 days. Hayes and Licht (1992) have shown that males and females differentiate in growth rate at the development of the gonads (approximately 6.6 cm/2.6 inches).9 The chart below is an extract from their paper, illustrating growth rates. It should be noted that a different diet and different conditions may result in slower or faster growth, but growth curves and divergence should remain the same relative to each other (this has been my experience).
|Postmetamorphic growth in body length in P. adspersus. Points represent means and vertical lines represent the standard error of the means (males, n = 7; females, n = 13). The arrow indicates the time of first appearance of differentiated gonads. The asterisk indicates the interval over which the size-specific growth rate (ln Δ [length]/ln Δ t) was statistically different between males and females. (Source: Hayes & Licht 1992) |
Natural Range & Habitat
Pyxicephalus adspersus is recorded in much of sub-Saharan Africa. Many records exist from before the splitting of P. adspersus and P. edulis (Dwarf or Lowveld African Bullfrog). The map below is based on data from before the split and it is likely not 100% accurate. Some sources list Nigeria as part of the species' natural range but this seems highly unlikely. It is interesting to note that this species ranges from temperate (the very southern extent of its range in South Africa), through sub-tropical and into equatorial regions, and at its greatest dimension the range is about 3,000 miles; truly massive for any species. Most of the published studies of P. adspersus have been carried out in South Africa, and this has implications: it is unlikely that the species' behavior is the same across the entire range given the difference in climates.
The habitat of this species is the dryer savanna of southern Africa. Frogs typically live in and around large pans that fill with water after rains and frogs can be found in the surrounding bush land while moisture persists in the area.
|Geographic distribution of Pyxicephalus adspersus across sub-Saharan Africa. (Source: Global Amphibian Assessment) |
With the appearance of so many variations of this frog which are obviously not the stereotypical Giant African Bullfrog (many do not grow larger than Lowveld African Bullfrogs, and colors vary greatly), it has become more and more apparent that the genus Pyxicephalus requires considerable attention from taxonomy scientists. It is a safe bet that what we refer to as the Giant African Bullfrog is largely confined to South Africa and neighboring countries. Sadly, at least in the USA, many unscrupulous vendors sell these smaller variants as Pyxicephalus adspersus / Giant African Bullfrogs, likely due to the demand by hobbyists for large, powerful frogs.
Captive Care & Housing
These frogs are among the easiest to maintain in captivity. Their simple requirements are a modest container such as a 60 liter (15 US gal) aquarium, suitable substrate in which to burrow, a container of water that they can easily enter and exit, and basic heating equipment to mimic their native climate. The care information presented here for Pyxicephalus adspersus is equally applicable to the other members of the Pyxicephalus genus, such as Pyxicephalus edulis (sometimes spell Pyxicephalus edulus).
Housing: Young frogs, less than 7.5 cm (3 inches) in length, will do well in a 15-20 liter (4-5 US gal) vivarium such as a sterlite box or a small glass or acrylic aquarium. These frogs are surprisingly agile, particularly when young, so a secure lid should be used. The frogs tend to be nervous as youngsters and this can lead to injury and falls, so it's best to avoid picking them up at all until they calm down. When cleaning the vivarium it might become necessary to handle the frog, however briefly. In such cases one hand should cup the frog and the other should be used to cover the frog to prevent jumping.
|A juvenile P. adspersus measuring about 5 cm (2 inches). |
Photo ©2008 John P. Clare / FrogForum.net
For adult female frogs, a 40 liter (10 US gal) vivarium is perfectly suitable. Adult males should be given a minium of a 60 liter (15 US gal) vivarium, but preferably a larger vivarium should be used. The height of the vivarium is not important but taller vivaria may be more suitable for planting/decoration. These frogs burrow extensively and have very strong hindquarters. As a result, plants should only be used in secure pots and not planted directly in the vivarium's substrate. We must also ensure that the plants are amphibian friendly because many plants commonly sold in garden centers are poisonous to animals.
A note on lids: a ventilated lid, such as the wire mesh vivarium lids sold in pet stores, should be employed. Lack of ventilation can encourage undesirable bacteria and fungi, and may foster the build-up of unfavorable chemicals such as ammonia from waste products.
Substrate: Most hobbyists use coconut fiber substrate which is sold under various brand names including "Eco-Earth". This is relatively cheap and is sold in dried bricks which, when placed in water, expand to many times the original volume. There are two main advantages to cocunut fiber as a substrate: it will pass through the digestive tract of the frogs without causing obstructions/impaction, and it is free of additives, parasites and other nasties. Its primary disadvantage is that it doesn't harbor any beneficial bacteria or fungi so it can sour, and it requires changing more frequently than natural substrates such as soil.
The main alternative to coconut fiber is additive-free top soil (or your own garden soil, provided it is free of pesticides and fertilizers). If you use one of the additive-free top soil products available at hardware stores rather than your own soil, ensure that it contains little or no large pieces of mulch, which is a common additive in these commercial products. The reason for this is that these frogs can accidentally ingest the substrate when they lunge for their prey and this can cause intestinal blockages/impaction. This is one of the most common causes of premature death in these frogs. Top soil doesn't sour/spoil as easily as coconut fiber due to the presence of helpful bacteria and fungi, and as a result it generally requires less frequent renewal. It is also cheap (or free if you use your own). Due to the impaction risk, almost all other substrates should be avoided unless they meet the criteria discussed here.
Whichever substrate you use, there should be enough so that the frog can bury itself completely if it desires. It's important to keep the substrate moist (not dripping wet though): if the substrate is too dry for too long, the frog's appetite will likely drop off and it may attempt to aestivate.
Some hobbyists use the terrarium moss products sold in many stores. There is a risk of intestinal problems if the frog ingests a significant piece of this material so use moss like this at your own risk. Short growing moss like that found on rocks in forests and shaded wet gardens is not an impaction risk.
|A nicely colored female P. adspersus. |
Photo ©2008 John P. Clare / FrogForum.net
Water Container: These frogs spend a large part of their time in water. A water container large enough for the frog to immerse itself, should it choose to do so, should be provided. It is important that the container can be easily entered and exited. The water should be free of the chlorine, chloramine and ammonia found in many municipal water supplies. This can be accomplished by using any aquarium dechlorinator product sold by most pet stores (and even Walmart in the US). These products have the added bonus of removing trace amounts of heavy metals (such as copper from water pipes).
Heating & Lighting: Daytime temperatures for these frogs during above-ground activity (i.e. when they are not aestivating) should be maintained at 25-32 °C (77-90 °F), ideally with a drop of a few degrees at night, though the temperature drop is not absolutely necessary. Heating can most easily be achieved by using a heat mat or an incandescent light. Heat mats are unobstrusive and best suited to glass vivariums. They are typically placed under one end of the vivarium or on one pane of glass. These frogs have been known to burrow down to a heat mat and then dehydrate and die. If a heat mat is used for them, it is wise to place it on a side pane of glass rather than underneath. Unfortunately, heat mats are not as effective when employed in this manner and therefore many hobbyists favor incandescent light bulbs as the heat source.
For a 40-60 liter (10-15 US gal) vivarium, a 50 watt incandescent spot light commonly sold in pet stores is ideal. This should be placed over one end of the water container so that the frog can find its preferred temperature by moving closer to or further away from the light. It is strongly advised the you purchase a ceramic light fixture sold for this purpose in order to minimize the risk of fire (these bulbs get very hot). One of the commonly available wire mesh screen lids is ideal as a cover onto which these light fixtures can be placed.
Provided that the ambient room temperature is not lower than about 20 °C (68 °F), a timer can be used to automatically turn the light or heat mat off in the evening to simulate night time. Photoperiod (how long the day lasts, even artificial day from a light bulb) may play a role in stimulating feeding and breeding behavior and a light period of 12 to 15 hours per day should simulate summer time well for these frogs. If the ambient room temperature does drop below 20 °C (68 °F), a side panel-fitted heat mat can be set on its own timer to come on at night to prevent the vivarium temperature falling too drastically. Ideally, a rheostat or thermostat should be used to keep the heat mat's output at a known temperature.
Foreword: African Bullfrogs are voracious eaters. The size of their mouth, their powerful jaws and the damage they can inflict with their odontoids mean that almost any animal that will fit in their mouths is a potential menu item. Dangling a finger in front of a frog's head is not a great idea; these frogs can deliver very painful and deep bites that bleed copiously.
Live or moving food elicit the best feeding response. However, the frogs can also learn to feed on pellets such as those used to feed salmon and trout in the aquaculture industry (for example, Purina Aquamax). The advantages of feeding live food are that there is no degradation in vitamin/mineral content and many live foods, such as insects, can be gut-loaded with nutritious foods in order to provide extra nutrition for the frogs. The primary disadvantage is that live food can pass parasites and diseases to frogs. Also, some animals, such as crickets and rodents, can inflict damage on frogs if not eaten immediately and left to wander the cage. Though rare, mice and rats have been known to inflict bite damage on frogs as they are being consumed. Sadly, many people are only interested in these frogs because they can tackle live large rodents such as rats and mice and there are plenty of videos on Youtube depicting such frog-rodent encounters. It's important to bear in mind that the predator-prey relationship is not always completely one-sided, and while it can be impressive to watch a frog overpower and swallow a live rodent, every time a significantly sized live rodent is fed to a frog we run the risk of injuring the frog, or worse.
Food items: In my experience keeping large amphibians for many years, a varied diet results in optimal growth and health. Most experienced keepers of African Bullfrogs feed one or two staple foods on a regular basis and feed a significantly different food item every few weeks. For example, a semi-adult frog can be fed cockroaches and night crawlers (otherwise known as the large earthworm, Lumbricus terrestris) every 2-3 days, punctuated by an adult mouse every 2 or 3 weeks. You can find an excellent list of nutritional values for amphibian foods at the Caudata Culture Web Site (including cockroaches, mice, chicken, quail and amphibians). While the nutritional values don't indicate it, frogs fed mainly with mammals like mice tend to become obese. The general explanation for this is that amphibians do not deal with mammalian tissue in the same way that they deal with invertebrates (animals without a backbone, like insects and worms).
Calcium and phosphorous are necessary to build bone mass and while the optimum ratio of the two in a food item varies depending on the species to which the food is being fed, a good guideline is to look for more phosphorous than calcium.
Wild-caught animals like crickets, rodents, birds, reptiles and amphibians invariably carry parasites of the gut, and potentially less obvious parasites such as lungworms. They may also be vectors (carriers) of bacterial and fungal diseases. Feeding a parasitized animal to your frog will almost certainly pass that parasite to the frog. This could have a significant impact on the frog's health and longevity. Deep-freezing these kinds of food animals for several weeks prior to feeding should kill almost all communicable parasites such as roundworms in the gut, but freezing will usually not rid the food animal of potentially communicable diseases. Therefore it is advisable to feed commercially farmed crickets, lab-bred mice, rats, and birds, and avoid amphibians and reptiles as food items completely. The following is a list of suitable foods for African Bullfrogs:
- Crickets: House or Brown Crickets, Acheta domestica, are the most commonly available. Wild crickets may carry communicable parasites.
- Locusts: higher meat:exoskeleton ratio than crickets but not available commercially in most warm climates due to pest concerns.
- Cockroaches: there are many species available and many frog enthusiasts breed their own - cockroaches offer a high meat:exoskeleton ratio and a better calcium:phosphorous ratio than crickets. Perhaps the most popular species for African Bullfrogs is Blaptica dubia, because the sizes of the different stages are compatible foods for many different animals and the adults are large enough to provide a good morsel for a large male African Bullfrog. This species is also a reasonably fast breeder. Cockroaches are relatively odor-free, straight-forward to maintain and feed, and very cost-efficient if you are feeding more than a couple of animals. If you do decide to breed them yourself, be sure to start with a colony of at least a couple of hundred individuals. Cockroaches make a great staple food. Wild cockroaches may carry communicable parasites.
- Silkworms & Hornworms: not as commonly available as most insects but good feeders nonetheless. A nice "treat" food.
- Waxworms: amphibians seem to find these incredibly attractive but they are quite high in fat content and low in calcium. Should not be used as a staple.
- Phoenix Worms (Soldier fly larvae): often touted for their high calcium and phosphorous content, a little on the small side for even a mid-sized African Bullfrog.
- Mealworms & Superworms: relatively high in fat and they have a particularly bad calcium:phosphorous ratio. Shouldn't be used as a staple.
- Earthworms (Night crawlers and others): one of the best staple foods in terms of protein:fat ratio, calcium and phosphorous content (and ratio). A great staple food. There are many types of earthworm and they vary in several important ways. Night crawlers, sometimes called Lobworms or Canadian Earthworms are the large earthworm, Lumbricus terrestris, commonly found in the pastures of northern latitude countries. They are often sold in the US as catfish bait. They require refrigeration to keep them alive for any length of time. They are hard to culture at home because their life cycle is relatively slow. They are eagerly accepted by amphibians. Most of the other commonly available earthworms are "compost" worms of various species. These worms reproduce in rotting vegetable matter and can be cultured at home (in fact you can buy commercial wormeries for composting home vegetable food waste). These are quite suitable as food for frogs but many species produce a distasteful fluid when stressed and this can make them unpalatable to amphibians. However frogs can get over this so it's worth persevering. One final note on earthworms: purchasing them from bait stores carries the risk that they have been contaminated with dyes or other chemicals that could be detrimental or even poisonous to your animals, so be careful when acquiring worms from sources other than live food vendors.
- Mice & Rats: rodents are a very nutritionally rich food but, as mentioned earlier, frogs don't deal well with mammalian tissue and so these should not be used as a staple/long-term diet. I feed thawed frozen due to safety concerns and convenience. If you find yourself using a lot of mice or rats, it pays to buy in bulk.
- Amphibians: nutritionally, amphibians are superb, but since all of those sold as feeders are likely parasite and disease vectors they are best avoided. On top of this, some are poisonous to a lesser or greater degree.
- Reptiles: feeder lizards invariably carry communicable parasites and they can also carry diseases. They are best avoided.
- Birds: some vendors sell lab-fed chicks/chickens and lab-fed quail. These are excellent foods but are best treated in the same way as rodents by feeding only occasionally. Avoid wild-caught or those raised outdoors due to parasite concerns.
Feeding schedule: Young African Bullfrogs (less than 6.6 cm / 2.6 inches long) should ideally be fed daily as much as they will eat in about 15 minutes. Sub-adult frogs should be fed every 2-3 days, again as much as they will eat in 15 minutes. Adult frogs can be fed similarly but frequent feeding of some foods (like mice and birds) will quickly result in obesity in adults.
Supplements: A varied diet should not require supplementation but there is probably no harm in providing vitamin and mineral supplements occasionally. Most pet stores sell two types of reptile/amphibian supplement: calcium powder and vitamin & mineral powder. Calcium powder is usually calcium carbonate. Some vendors tout their product as being superior because of its source or the size of the granules, but in reality the animal absorbs so little of it from one feeding that these claims are meaningless. Vitamin & mineral powder contains a variety of trace elements and vitamins. These vitamins and minerals tend to degrade over time so it's a good idea to look for a manufacture date, packing date or shipping date on the package to try to ensure it hasn't been sitting on the shelf for years. Again, so little of the powder is absorbed in one feeding that some degradation is unlikely to matter. Administering either powder is done by dusting a food item prior to feeding. This can be accomplished by using a margarine tub or a jar, placing some powder in it and shaking a food item in the container while the lid is on. When I am supplementing I will dust the first food item (unless it's a tiny thing like a small cricket, then I will dust more than one) and leave the rest undusted. I supplement with each type of a powder once a week, but never on the same day - there is evidence that using both at the same feeding may reduce the uptake of one or more of the components.
How to feed: There are a couple of important things to keep in mind when feeding one of these large frogs. They can move very fast and they usually don't discriminate between fingers and food. Most keepers will feed using a forceps. A rubber tipped forceps (or hemostat) is advisable - large frogs can damage themselves when lunging at food held in uncoated forceps. Another important consideration is that these frogs have been known to swallow their substrate accidentally when going for food. I like to feed my frogs in their water bowls to help prevent this (if the frog is not in the bowl I either encourage it to enter the bowl or just lift it carefully and put it in the water).
Aestivation & Breeding
Aestivation: These frogs breed after a period of dormancy known as aestivation. Earlier in this article I mentioned that these frogs aestivate for several months while awaiting the first heavy rains of summer. This period of dormancy ensures that they retain enough water to survive until favorable conditions return above ground. This is accomplished by burrowing deep into the soil and then shedding many layers of skin, which forms a paper-like cocoon around the frog, leaving only its nostrils exposed. The frog exists on its fat and moisture reserves. To maximize these resources, it enters a state of very low metabolic activity. Only the water from heavy rains can penetrate to their underground chamber and this is the trigger that awakens them.
In captivity, these frogs will often burry themselves completely (or with just their eyes showing). This is not aestivation and the frogs will almost always emerge for food. True aestivation involves the frog leaving the water and digging down quite far, if it has the depth of substrate to do so; in captivity they have been known to attempt to aestivate on the surface without substrate if conditions are harsh enough. Often the frog will dig so far that it reaches the bottom of its vivarium. To stimulate aestivation it's a good idea to let the surface of the substrate dry out and to lower the water level of (or completely remove) the water bowl. Heat provided by lights is ideal for stimulating aestivation because the light heats the substrate surface, not what's underneath. In the low humidity that results from this situation the frog will bury itself and enter aestivation. The frog will often not eat just before aestivation and it will clear its gut. Once the frog has been buried for several days, it is not necessary to keep the temperature of the vivarium very warm. In the wild, underground temperatures are very stable and even close to the surface the temperature rarely rises above 20 °C (68 °F). In fact, these frogs typically aestivate through the colder parts of the year (which are also the driest). Just ensure that the temperature cannot fall below about 13 °C (55 °F) and mist the top of the substrate every few days to prevent the substrate completely drying out.
Well-fed frogs can be maintained like this for 3 months or more (as mentioned earlier, 10 months in the wild is possible, though a little extreme). The frogs can be "woken up" by adding copious amounts of water to the substrate such that it reaches the aestivating frog and is absorbed by the skin cocoon. The frog should emerge within a few hours, at which time it will want a water bowl and lots of food.
Breeding: Breeding African Bullfrogs in captivity without the aid of hormones is considered quite an accomplishment. To my knowledge no one has published (either in a journal or on the Internet) how to breed these frogs successfully with the normal facilities available to pet-keepers. As a result, what I am about to present here is based on educated guesswork and some advice from Zoo professionals.
|Giant African Bullfrog Tadpoles, Pyxicephalus adspersus, a few days after hatching. |
Photo ©The Frog Ranch.com
It is quite feasible to interest the male frog in breeding simply by putting the frog through a few months of aestivation. There have been several accounts of amplexus resulting from this, but none that I'm aware of that resulted in egg-laying by the female. In these captive breeding attempts, the female not laying is quite a common trend in anurans that undergo aestivation (cf. large toads like Bufo alvarius). The event that triggers the female's willingness to lay is not known with certainty, but there are some obvious factors that should be taken into account. Firstly, most people aestivate their frogs at the temperature of the heated vivarium. Simply observing the climate of their native countries, and doing some literature research on underground temperatures, indicates that the natural temperatures of aestivation should be much lower than normal vivarium temperatures. Having talked to sources in the Zoo field who breed large anurans like Pyxicephalus, their feeling is that the aestivating frogs should be maintained at the kind of temperatures I mentioned a few paragraphs ago. This alone may be sufficient to trigger a laying response from the female.
The second important factor is likely a change in pressure. When the heavy rains come in the wild, they are delivered by low pressure storms which provide a relatively sudden change from the high pressure dry conditions before they arrive. It is likely that the frogs can detect this and it could be an additional stimulus for breeding. To mimic this in captivity should not be too difficult: monitor your local weather while the frogs are aestivating and be ready to wake them up after a large rainstorm begins, after a period of at least a few weeks of dry weather. If you want to keep track of the barometric pressure in your area so that you have a quick indication of significant pressure drops to aid your breeding efforts, consider investing in a barometer (there are many kinds - that link is just an example). None of this is a sure thing but if breeding your frogs naturally is your goal, then following this advice certainly won't can't hurt. Some hobbyists speculate that having multiple breeder animals present together might help encourage laying but if this were the natural behavior then these frogs would never colonize new habitats. The only merit to this would be if one or two animals have not truly entered breeding mode, having others as backups might help.
|Giant African Bullfrog Tadpoles, Pyxicephalus adspersus, nearing metamorphosis. Front legs are visible on one of the tadpoles in the top left of the photo. The ridges and markings of metamorphosed froglets are becoming visible. |
Photo ©The Frog Ranch.com
When the frogs do breed, they prefer to lay in water about 7.5 cm (3 inches) deep. This allows the female to raise her hindquarters out of the water to enable fertilization to take place in the air (see much earlier in the article for more on this). These are large frogs so a container with quite a few square feet of water is advisable.
Raising the Young: As mentioned earlier, the number of eggs is usually in the early thousands. The eggs will hatch within 48 hours at a temperature of 29 °C (84 °F). Tadpoles will metamorphose in less than 30 days, at which point they should be kept separately or in very small groups unless fed very well, in order to prevent cannibalism. Haas raised his tadpoles on a simple diet of Tetramin fish flakes.9 They are typical omnivorous ranid tadpoles and they can be fed suitable diets like the pellets used to feed rabbits and guinea pigs, perhaps mixed with a little dry dog/cat food (beware that meat-based foods will foul the water rapidly so some method of filtration should be considered). Keep in mind that you might be dealing with over 4000 tadpoles that grow at a very fast rate. Water quality and space should be your primary concerns, and unless you intend to raise 4000 frogs, it would be advisable to have a wholesaler ready, or a lot of hobbyists who will buy or take the offspring.
The Giant African Bullfrog, Pyxicephalus adspersus, is one of the most popular frogs in the pet industry. Its large size and the ease with which it can be kept mean that it is sure to remain popular in the future. I hope this article has given you useful information for your decision to acquire one of these frogs, or hopefully it has helped you learn more about a pet that you already have. Please feel free to comment on this article using the form below.
- Thank you to Kim Thomas for permission to use the tadpole photos. Kim is the owner of The Frog Ranch, the main commercial breeder of Pyxicephalus in the US, and they also breed other large frog species. Their info page for the species has some great photos and brief care information.
- Passmore, N.; Carruthers, V. 1999. South African Frogs: A Complete Guide; New Holland Publishers, Ltd.
- Balinsky, B. I.; Balinsky, J. B. V. 1954. S. Afr. J. Sci. 51, 51-58.
- Kok, D.; Du Preez, L. H. 1989. J. Herpetol. 23, 435-437.
- Cook, C. L.; Ferguson, J. W. H.; Telford, S. R. 2001. J. Herpetol. 35, 310-315.
- Channing, A.; Du Preez, L.; Passmore, N. 1994. J. Zool. Lond. 234, 141-148.
- South African Weather Service data for Johannesburg, Gauteng, South Africa for the 30 year period 1961-1990.
- van Wyk, J. C. P.; Kok, D.J. 1992. J. Herpetol. Assoc. Afr. 40, 56.
- Haas, A. 1999. Zoomorphology 119, 23-35.
- Hayes, T.; Licht, P. 1992. J. Exp. Zool. 264, 130-135.
- Pyxicephalus adspersus geographical distribution at Global Amphibian Assessment.
- AmphibiaWeb: Species Information Page for Pyxicephalus adspersus. Accessed: October 28th 2008.
First published in September 2008. Last updated Thursday June 24th 2010.
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