Notes on Caring for Thumbnail Frogs

First a note on my policies regarding sales of thumbnail frogs, and their replacement in the event of their death after receipt. All my policies regarding live arrival of frogs apply 100% to thumbnail frogs, however after arrival I tend to be less generous with my replacement policy. I assume when you order these frogs that you are a knowledgeable hobbyist, prepared to feed and care for these frogs as your experience dictates. I assume you are aware that these frogs are much more delicate than the larger frogs, and that you realize that these frogs are very prone to being stressed out by tankmates and shipping, and will sometimes die suddenly for no apparent reason. The frogs I ship out are typically approaching sub adult size, and if kept together in a group of three or more, in a tank like a ten or twenty gallon, a variety of things may happen, including sudden breeding behavior, and also possibly sudden death of one or more frog in the group. I will be most inclined to replace frogs that are kept as I suggest for a period of a month or more, depending on the frog. If kept individually in small tanks or shoeboxes, and they fail to thrive, notify me as soon as possible for assistance in trouble shooting these problems, and a replacement can often be made if the frog dies. However frogs placed in group situations will most likely not be replaced.


Thumbnail frogs have always held a special place in the hearts of the dart frog enthusiast. In the early days of this hobby, most hobbyists had a hard time finding and affording thumbnail frogs, and the specimens they were purchasing were often from Europe. These freshly imported frogs often died, and this is part of the reason it took so long to get these frogs established in the US hobby. Now they are becoming much more readily available to froggers in this country, and the quality and health of the specimens is generally pretty high. The selection and relative ease of acquisition makes this a “golden age” in the frog keeping hobby. In this sheet, I would like to cover a few things that may seem obvious to many, but perhaps are not to every one. In addition I will offer some ideas for sexing and keeping these frogs.

Observations and thoughts regarding keeping them together

First, the thumbnail frogs sold here are not babies, but juveniles or sub adults, depending on the frogs and the particular moment your frogs are sold and shipped to you. In most ways this is an advantage over the babies that some vendors may be selling, as of course these frogs will be much more robust, having had an extra two months or so of feeding before going to you. However these sub adult frogs may be even more challenging to keep together, as their emerging sex hormones may make it even more likely that they will rapidly set up territories and intimidate one another. Thumbnail frogs are, in my experience, at least as competitive and territorial as any other dart frogs. Despite their tiny size, they are capable of intimidating their tankmates through a variety of tactics which we are unlikely to ever see. Additionally, they are quite prone to stress, and so keeping them in groups, especially in smaller tanks, such as tens and twenty gallons, is somewhat risky.

In some cases they establish territories right away, and a frog out of four or so may be “outcast” within hours of the group going in the tank. In some cases the outcast frog will remain in one location, or hide, and die within two or three days of going into the tank. In other cases, you may not really see any obvious signs that the frog is an “outcast” but it will simply turn up dead one day. My suggestion for you if you wish to keep three or four thumbnail frogs in a group setup, is to use a larger tank. A forty gallon may be the smallest safe size to house this size group. On the other hand, you can also take your chances in the smaller tank, some losses should be acceptable to you if this is your approach, and hopefully you won't have any.

I know of many cases where hobbyists are keeping quite a few thumbnail frogs in small tanks, and having great luck. A couple of friends of mine keep seven to ten thumbnail frogs in tanks about twenty gallons, some smaller, some larger, and they breed prolifically for them. I have wondered a good deal about this, and have come to the conclusion that possibly the frogs do well if somewhat over crowded, so that they are not really able to set up territories. I have personally never had that many frogs that I felt comfortable putting in one tank, but have tried it with between three and five. In two separate instances, I kept five frogs, D. imitator in one case, D. reticulatus in another, in a ten gallon. My results were pretty similar, the frogs bred, but slowly over the course of about two years, the groups both dwindled to a pair. Both tanks were set up in the mid nineties, and the remaining pairs of frogs lasted well into this century, so I feel it is obvious that the three deceased frogs died of stress in each tank.

At this point in time, my strategy is to keep pairs of thumbnail frogs in my tanks. I keep them in tanks that are probably about sixteen gallons, they are ten wide, by twenty inches long, and about seventeen inches high. Out of forty or so thumbnail tanks, I have about three or four that contain more than a pair, the rest are all pairs.

Getting them setup and sexed…..

My method for getting my frogs sexed and paired up is as follows. To start with, I keep my frogs in plastic shoeboxes, on a leaflitter type substrate, as they morph out of the water, or when I get them from another hobbyist. The substrate should be quite moist, and no holes are made in the container, as the humidity needs to be high. Temperatures in the mid seventies are best, over eighty degrees is to be avoided. As I was starting out with these frogs, I would keep two or even three in a shoebox, as babies, but I found that they didn't do as well with another frog in the box, so I went to keeping them individually in the shoebox. I find it amazing that a frog the size of a peppercorn could negatively influence another frog the size of a peppercorn, in a space six inches wide by fourteen inches long, but I have seen enough evidence of this to be convinced that something was going on between the two frogs in these containers. I raise them till they are large enough to at least guess what sex they are, at which point, I then take what I hope to be a pair, and set them up in a tank, and watch them closely for a couple of days.

Guessing the sex of these frogs can be difficult, but the clues you are looking for are the differing body shapes and sizes of the two sexes. Males have a shorter body, females longer, and females are generally a little stouter than males. These differences become more and more obvious as they get older, but are often not clear cut until the animals begin breeding.

Depending on the species, they are usually big enough to begin guessing their sexes at five to seven months. It will often be obvious within an hour that I was right, as the pair will be following each other around the tank. If no interaction is witnessed within a day or two, I may either separate them and try again, or add another frog to the mix. I always watch very closely at this point, for with three frogs in the tank, things can happen fast. I sometimes find one frog waiting by the door of the tank, and not moving much from this spot. In many cases, I believe this frog would be dead within a couple of days if left in the tank. In my observations, it is both sexes who are territorial this way, but the few cases that I have had where a productive trio is established, it has usually been one male and two females. Several species seem more agreeable to this trio arrangement than others, I will go over that shortly.

Setting up the tank for breeding is pretty simple. These frogs tend to prefer temps in the low or mid seventies, and very high humidity. Breeding most of these frogs without the tank completely saturated with humidity is generally not possible. However no water feature or other special “tricks” are required, to achieve this humidity level one must simply seal the tank up well, with no holes for ventilation. Temperature doesn't seem to be that critical, but rapid changes in temps, such as a sudden rise (over a few hours) from the mid seventies to the mid eighties seem to be dangerous, and will definitely stop any breeding even if the temp change doesn't hurt the frogs. Conventional wisdom has always been that the frogs need the cooler temps, but my observations tell me this is not as important as relative temperature stability. The frogs like a well planted tank, but particular types of vegetation are not critical. Bromeliads will be enjoyed by all species, and any other terrarium appropriate plants will be fine.

Eggs, tadpoles and froglets…..

These frogs can be very loosely broken up into two groups, the “imitator” group, (imitators, intermedius, reticulatus, fantasticus, lamasi, etc) and the ventrimaculatus group, consisting of the vents and amazonicus. The vent group frogs prefer to lay their eggs under water, at waters edge. Film canisters sat at an angle on the bottom of the tank, filled with water, work well, and they will use bromeliad axils also, although you may wish you hadn't given them a bromeliad if they pick the wrong side of it to lay in and you can't get the eggs out easily. These frogs typically lay larger clutches of eggs, up to the low teens, but more typically six to ten. These eggs are tiny, and black. They should be removed and placed in a Petri dish covered with ample water. Tadpoles should be raised singly, and like any other dart frog tadpole. Water temps for tadpoles should be maintained in the mid seventies.

The imitator group frogs lay clutches of larger eggs, smaller than a tinctorius or such, but larger than vents. The clutches are typically two to four eggs. The eggs are generally a light to dark grey. The eggs may be laid in film canisters placed about the tank, or on Petri dishes placed in hide spots. They also often lay on the glass, plant leaves or any other smooth surface in the tank. These frogs tend to change laying spots if you remove their eggs. The eggs can be removed by gently rubbing them off with your thumb or lifting them off with a credit card or other stiff object. Them put them in a Petri dish, and put a small puddle of water around the egg clutch. Do not cover the bottom of the Petri dish with water, they do not like to be saturated with water. Care of tadpoles is straight forward. Diet for all dart frog tadpoles, including thumbnail frog tadpoles here is the mix of Chlorella and Spirulina, blue green algae. Many species seem particularly delicate as tadpoles, such as reticulatus, fantasticus, and amazonicus. Water quality is critical, poor quality water quickly kills these tadpoles. I recommend using generic bottled spring water if in doubt of your water quality.

The froglets of these frogs are of course quite small, and while some are pretty easy to raise, many are fairly difficult. Standouts in the difficult to raise category are reticulatus, and amazonicus. Other species may be difficult, any given pair may produce froglets which are too small to easily raise. Springtails are the food of choice for the smaller froglets, such as retics and amazonicus. However the imitators, fantasticus, and intermedius froglets among others should be able to take the melanogaster fruit flies right out of the water.

A couple of side notes….

The imitator group frogs are part of a group of dart frogs which are called facultative egg feeders. They will carry their tadpoles to a water source, (in this case the male does the carrying) and then the male will call the female to the tadpole and court her to lay small infertile “food” eggs for the tadpole. If you have a pair of these frogs laying for you, and you suddenly notice that they stopped, this may indicate that they have taken one or more tadpole off to a film canister or bromeliad leaf axil, and are feeding it. In most cases they wont lay any more reproductive eggs while this is going on. You can safely pull the tadpole and begin feeding it normal food, or if you like you can continue to observe them courting.

It has been my observation that these frogs run heavy to males. I recently purchased ten of a species, and got nine males. I would say that you should expect to get at least two males for each female in purchases of unsexed frogs. Occasionally I speak to someone who has the opposite perspective, but try finding extra females of any of the thumbnail frogs, and I think you will see my point.

Please feel free to make any contribution to this that you feel is relevant, and I welcome dissenting opinions on these observations. Keep in mind that I realize that there are exceptions to these guidelines regarding housing and such, but I do feel that this method is safer in the long run.