Care and Breeding the Vietnamese Mossy Frog
Mossy frogs of the genus Theloderma are like no other.
Like many good things, it all started with a book. When I was a child, a weekly visit to the library resulted in some frustration. I had checked out a book on reptiles and amphibians only to come across a photo that was supposedly of a Vietnamese mossy frog (Theloderma corticale). But for the life of me, I could not find the frog in the photo! I would stare and stare but not see the frog, and every time I returned to the library I would pull out the same book (exactly which book that was, I no longer remember), turn to the same page and stare at that photo yet again in the hopes of finally making out what I was sure must be an amazing, if not actually invisible, anuran. Finally, I saw an eye. Then, a leg. And so goes the amazing camouflage abilities of the mossy frogs of the genus Theloderma.
Mossy frogs make amazing display animals — you can use red or “moon” nightlights (not heat lamps) to illuminate their enclosure at night so you can better observe them when they’re most active.
Theloderma are certainly a unique genus. The name literally means “bumpy skin,” in reference to their notably rough dermis. With the exception of a few species, notably T. licin and T. laeve, this bumpy skin is a hallmark of the genus and greatly aids the frogs in blending into their environment. In addition to the common name “mossy frogs,” they are sometimes also called bug-eyed frogs and warty tree frogs.
The genus Theloderma consists of about two dozen species native to south and east Asia. Of these, only four or five are encountered with any regularity in the U.S. pet trade: the Vietnamese mossy frog, the mini mossy frog (T. bicolor), the Vietnamese bird poop frog (T. asperum) and the Tonkin bug-eyed frog (T. stellatum). Wild-caught imports of the smooth-skinned bug-eyed frog (T. licin) are occasionally available but are notoriously difficult to acclimate.
Longevity data is very scarce for mossy frogs, but some Vietnamese mossy frogs have been documented to live well into their teens in zoos, so a lifespan of 20 years or longer is not out of the question.
Mossy Frog Habitat and Captive Housing
These masters of disguise live in rain forests. Most species are semi-aquatic, living around and breeding in tree holes or rocky pools. Fortunately, this habitat is easily replicated in the terrarium. A glass aquarium with a screen top or a front-opening glass terrarium are both great choices in which to keep Theloderma. When setting up the habitat, take into consideration the adult size of the species you’re planning to house. Larger species, such as the Vietnamese mossy frog, should have about 10 gallons of space per frog. Three to four frogs of the smaller species, such as the mini mossy frog and bird poop frog, can easily be housed in a 10- to 20-gallon aquarium.
Because these frogs are semi-aquatic, water is important and will play a major role in their enclosure design. The frogs do not require running water, however, and I, personally, have kept hundreds of mossy frogs in enclosures with stagnant water — no filtration required! Oddly enough, I’ve noticed that water that is too clean can lead to the development of eye problems.
Place 2 to 4 inches of water into the enclosure, and add several cork flats and tubes to provide land areas. I use reverse-osmosis water that has been reconstituted with R/O Rx, a product that adds minerals and trace elements back into water to make it safe for herps. Toss in an Indian almond tree leaf or other tannin-rich source, such as oak or magnolia leaves or a few drops of Blackwater Extract to put tannins into the water and drop its pH. The water may be a bit yellowish or brown in color, and look like tea, and this is how your mossy frogs will like it. I change about two-thirds of the water every two to three weeks.
Because they’re living on water, mossy frogs do not need to be misted often, though they must be kept at higher humidity levels of 60 percent or higher, or they can dry out. I generally mist two or three times a week to wash any fecal matter off the cage furnishings or glass and down into the water.
Cage décor can be very simple. I use cork tubes and flats to provide hides, perches and egg-laying sites. In my experience, mossy frogs love to lay their eggs on the insides of partially submerged cork tubes, so that the tadpoles can fall into the water when they hatch. Live or artificial plants can be included, as well. Personal favorites of mine include pothos, peace lily and water lettuce. If using live plants, you’ll want to use a light over the enclosure. I keep my frogs in a rack system, so a 4-foot shop light with one 6500K T8 does the trick. Basically, any light that’s appropriate for plants (as opposed to lights that are used for heat) and fixture that will fit over the top of your enclosure will work. Mossy frogs are nocturnal so any lighting provided is strictly for the plants.
Mossy frogs make amazing display animals — you can use red or “moon” nightlights (not heat lamps) to illuminate their enclosure at night so you can better observe them when they’re most active. They will thrive in a properly constructed naturalistic vivarium; use your imagination when building their habitat, as waterfalls, live moss, and the like are all appreciated and utilized. Theloderma are also great candidates for paludariums and can be housed with small, peaceful fish such as white cloud mountain minnows (even though a fish may turn into an occasional snack).
A word of caution: Watch the temperature! Temperatures in the low 70s and 60s Fahrenheit are ideal, and cooler temperatures are fine down to about 50 degrees. If you are unable to keep your mossy frogs below 80 degrees, I strongly recommend you consider keeping a different pet, as higher temps kill mossy frogs!
Mossy Frog Feeding Tips
Mossy frogs are insectivores and thrive on a diet of gut-loaded crickets. Other appropriately sized feeder insects, such as wax worms, Phoenix worms, Dubia roaches, and even small hornworms may be offered via feeding tongs. Make sure all feeder insects are dusted with a quality vitamin and mineral supplement.
Offer food to your frogs shortly after lights out. Within 10 minutes of darkness mossy frogs become active and will eagerly look for food. Crickets can be dumped directly onto the cork tubes or flats, or placed into a deli cup that can be floated on the surface of the water. Either way, some crickets are bound to drown; these can be removed during water changes. If your mossy frogs breed, tadpoles will eagerly consume any deceased crickets.
As a rule, offer prey items that are no longer than the distance between a frog’s eyes. Theloderma eat less than many other frogs I’ve worked with; adult animals will generally eat four to six prey items two to three times a week.
More Captive Breeding is Needed!
While captive breeding of Theloderma is more common than ever before, the demand for captive-bred animals still far exceeds their availability. Some species are maintained by only a few breeders in the U.S. (up until a few months before this article was written I was the only hobbyist in the country that was producing T. bicolor, at least with any regularity). If you plan on keeping mossy frogs, please consider breeding them. Captive propagation is relatively easy, and every frog produced in captivity is one less frog taken from the wild.
Tadpoles need to be raised at cooler temperatures in order to produce females with any regularity. By raising them in water temperatures between 55 and 60 degrees, the ratio of resulting females to males can be about 1:4. If tadpoles are raised at room temperatures they tend to highly skew male. I once raised over 30 Vietnamese mossy froglets up to adulthood, only to find that every single frog was a male! Because of this, I strongly recommend tracking down a breeder who rears tadpoles in cooler conditions and purchasing as many mossy frogs from that breeder as you can. (The cooler-temps-result-in-more-females rule does not seem to apply to some of the lowland species, such as T. asperum. Even at room temperature, sex ratios of those species are much more even.)
Mossy frogs are relatively easy to sex once you know what you are looking for, but sex is not as obvious as with many other frog species. First, you’ll want to make sure you have mature specimens. For most species of mossy frog, this means the frogs are at least 8 to 10 months old. Females are larger, with wider heads and shorter snouts than males. Male mossy frogs possess well-developed nuptial pads on their forelegs. These pads are found on the “thumb” of the frog, and appear reddish and swollen during breeding season (see photo). Nuptial pads help male frogs hold on to females during amplexus, while the frogs are mating. Females may exhibit underdeveloped nuptial pads, so be careful when sexing your frogs.
Male mossy frogs will generally call at night, sometimes at a very early age. I once had a 4-month-old Vietnamese mossy frog very nearly get me kicked out of a hotel after it started hooting at night. The call resembles a mechanical owl, and consists of a beautiful hooting melody. Mossy frog calls can be loud, but their melodic nature makes them easy to fall asleep to (at least for me).
The Four Most Common Mossy Frogs
Below are some details about the mossy frogs U.S. hobbyists are most likely to be able to find.
Vietnamese mossy frog (Theloderma corticale). Long considered the mossy frog, this is the largest of the commonly available (figuratively speaking) species of Theloderma in the hobby, with adult females approaching 3½ inches in length. While it is the most commonly available species, and is easily bred, finding females can be frustrating.
In the wild, Vietnamese mossy frogs live in evergreen rain forests in northern Vietnam, and may spread to neighboring China and Laos. They inhabit water-filled tree holes or rocky pools, where they easily blend into moss and lichen.
Mini mossy frog (T. bicolor). This small member of the genus is relatively new to the pet trade, having only been available in substantial quantities in the past few years. A small number of animals are imported every year from Vietnam, where it lives in tropical montane forests. Large adult females may reach 2½ inches, though typically remain closer to 2 inches.
This species has special meaning to me, as my wife and I were lucky enough to come up with their common name after we began to produce animals in 2014. Since then, we’ve introduced over 200 froglets from three bloodlines into the U.S. hobby. Due to its especially hardy disposition, the mini mossy frog is easy to keep.
Vietnamese bird poop frog (T. asperum). As its common name suggests, this frog looks like it’s coated in bird poop! Mimicking avian fecal matter as a means of staying off the dinner plate, the Vietnamese bird poop frog is primarily white, tan, and brown, with ruby-red eyes. It inhabits lowland rain forests from India to Sumatra, with frogs commonly being imported from Vietnam. At just over 1 inch in length, T. asperum is one of the smallest members of the genus. This species can handle temperatures several degrees warmer than other Theloderma, and have a fairly even sex ratio of males to females.
Tonkin bug-eyed frog (T. stellatum). This species is not commonly available in the U.S. hobby, with imports seemingly nonexistent. The specimens that can sometimes be found are descended from animals bred at a zoo in Texas. This is another smaller mossy frog, superficially resembling a darker version of T. asperum. Orange coloration is sometimes visible on exceptional specimens. Tonkin bug-eyed frogs can be found in lowland rain forests of Vietnam and surrounding countries, where their biggest threat is habitat destruction. —Zach Brinks
Once you’re fairly certain that you have at least one mossy frog of each sex, nothing very special is needed to induce breeding activity other than housing them together and offering a bit more food than usual to ensure they’ve got plenty of fat reserves. Provide plenty of partially submerged cork tubes with an inner diameter of at least 3 inches. Begin doing weekly water changes using cool water. Most of the time, the frogs will be observed in amplexus within a few days. Eggs will be laid on the underside of the roof of cork tubes, or plastered to the underside of cork flats tilted at an approximately 45-degree angle.
Clutches can be three to five eggs for smaller species, and up to 25 or so for larger species. Many small clutches may be laid by the same female over a period of several days, although two to six weeks between breeding activity is more common. Mossy frogs may breed year-round, but a few months of breeding activity is generally followed by several months of nothing. If your frogs continue to breed for more than four or five months, you may want to separate the sexes to avoid burnout.
Egg and Tadpole Care
Egg care is very simple with Theloderma — leave them where they lay! As long as proper water conditions are met, the tadpoles will wiggle their way out of their eggs and drop into the water after 10 to 14 days. Mossy frog tadpoles are not cannibalistic, and I have yet to witness an adult attempt to eat a tadpole, so I leave the tadpoles in with the adults. During this period, the tadpoles mainly eat fecal material from the adult frogs and drowned crickets, though I supplement with Josh’s Frogs Aquatic Frog Food.
When the time comes for the next water change in the adults’ enclosure, I move the tadpoles to their own rearing tanks. These are simple, 10-gallon aquariums with about 4 inches of water in the bottom (same reverse-osmosis water as used in the adults’ enclosure), with several Indian almond leaves added. The tadpoles munch on the leaves, and tannins released by the leaves imbue the water with natural antimicrobial properties. I feed about one pellet of Aquatic Frog Food per tadpole two times a week, and change half the water weekly. After several months (up to six to eight), tadpoles develop back legs, then front legs, and finally climb the glass walls of the aquarium to leave the water. At this point, they’re removed from the tadpole tanks and transferred to a grow-out terrarium.
A setup for mossy froglets is simple. About 1 or 2 inches of reverse-osmosis water is provided in another 10-gallon aquarium , along with lots of floating cork flats. I do not provide cork tubes to young froglets, as I want to be able to easily observe them to ensure everyone is eating and growing normally. I do include a few cuttings of pothos, which quickly roots and grows right in the water.
I feed young mossy frogs every other day. Even freshly metamorphosed frogs, because they emerge from the water quite large, are typically able to consume ¼-inch crickets.
Froglets are housed this way for two to four months before they’re moved to a larger adult enclosure, if needed (depending on the species).
If you’re looking for a frog and love the less common, unusual, or downright strange, then frogs of the genus Theloderma may be right for you. When cared for properly, they are undemanding pets and certainly entertaining and rewarding to keep. Straightforward to breed, mossy frogs can also make a fun breeding project that may even help offset the cost of maintaining them. While they are not yet widely available and may take a bit of work to find, mossy frogs are well worth the trouble!
Zach Brinks has been keeping and breeding various reptiles and amphibians for over 20 years. Heading the animal breeding operations at Josh’s Frogs (JoshsFrogs.com), he oversees the breeding of dozens of different species of anura. With a BS in biology from Michigan State University, Zach works to produce healthy, captive-bred specimens and to reduce the demand for wild-caught animals.