Feeding Dart Frogs: A look into the culture of Fruit Flies and related topics

Feeding Dart Frogs: A look into the culture of Fruit Flies and related topics

     Dart Frogs are visual predators that look for movement to lock in on a prey item. Therefore live prey items are necessary to elicit a feeding response. Since the large majority of Dart Frogs are microphagus (small mouthed) very small prey items are required. There are several small invertebrates that dart frogs will consume as food; these include springtails, pinhead crickets, dwarf isopods, bean beetles, fire-beats, termites, and fruit flies. This article will focus on fruit flies, which have established themselves as ubiquitous feeders for dart frogs.

A mix of supplement-dusted Hydei and Melonagaster Fruit Flies. 

     Fruit Flies of the genus Drosophila, specifically D. melanogaster, are one of the most studied organisms in biological research. Their popularity as a model organism can be attributed to a combination of reasons, two of which with relevance to our use of them is their high fecundity (potential to bear offspring) and short generation time. These traits make them ideal prey cultivars able to quickly produce large numbers of individuals.

     The ease of production is one of the biggest reasons fruit flies have established themselves as the main diet of dart frogs in captivity. Another important reason fruit flies are the preferred choice is their ease of digestibility. Many other small insects such as bean beetles aneed pinhead crickets have a hard exoskeleton which can be difficult for the frog to digest, and sometimes lead to health problems such as a prolapse. For these reasons they should not be relied upon to be the main diet for most dart frogs.

The wingless fruit fly Drosophila melanogaster goes hand-in-hand with keeping dart frogs in captivity.

     The specific D. melanogaster fruit flies that are cultured as prey items for dart frogs are typically a wingless phenotype. These flies completely lack wings, and are therefore incapable of any flight. Their appearance and locomotion are similar to that of a small ant. In addition to D. melanogaster another species of fruit fly often used to feed dart frogs is Drosophila hydei. D. hydei have some slight differences from D. melanogaster, the most obvious being a slightly large size. Also the D. hydei cultured as prey items for dart frogs are typically a “flightless” phenotype. These flies do have wings and are able to glide, but the mis-folding of structural proteins prevent them from taking flight. An interesting note is that at warmer temperatures Hydei cultures may regain the ability to fly! Along with the Wingless Melanogaster and Flightless Hydei there are other varieties of both that are available for culture.

The wings on Drosophila hydei allow for a greater surface area for supplement dust to adhere to.

Culturing Fruit Flies

     The preferred container in which to culture fruit flies with the purpose of using them as a feeder insect is the 32oz deli cup. These 32oz cups are of an adequate size to support a culture large enough to maintain a sustainable population despite being harvested from regularly. One culture per week should be made for every 2-3 frogs, resulting in a set of cultures that are staggered in age. Around 1-1/2 weeks from being made a culture will start producing flies, and the cultures should be disposed of after reaching an age of 4-5 weeks.

A freshly made fruit fly culture.

     In addition to the cup a fruit fly culture consists of flies, the media, a substrate, and the lid. Some notes on each of those below.

     A fruit fly culture will be started by inoculating it with around 50-100 flies, this is around a teaspoonful. It is important to use a large enough number of starter flies when making a culture to ensure it reaches it’s full potential. These flies are taken from an existing culture. Ideally these starter flies are sourced from a relatively young culture in an effort to reduce any transfer of pest mites into the new culture. Dusting these starter flies with calcium powder should also be done, as the dusting process will knock mites off of the flies. Mites will compete with the flies which reduces the number of flies the culture produces, this being the reason efforts should be made to avoid mites. More information on controlling mites will be discussed later.

     The media is an essential part of the fly culture. This will serve as both the food source as well as an egg-laying medium. There are many commercially available media mixes, as well as recipes found online that can be made at home with ingredients found at the grocery store. There should be 1”-2” of media at the bottom of the fly cup. The consistency of the media should be similar to oatmeal or yogurt. Thickening ingredients, usually potato or oat-based, will solidify the media as it sets. Media ingredients should not be kept near fruit fly cultures to prevent any possible mites from leaving the fly cultures and infesting the media ingredients. Pro-Tip: While not all media mixes require the use of boiling water when making new cultures doing so is another step that can be taken to sterilize the media for a clean start.

     A successful fly culture will result in thousands of flies, and all these flies need physical space in which to stand. There must also be ample room for fly larvae to attach themselves while pupating. This need for surface area is most commonly filled by wood wool, also know as excelsior. Typically made from Aspen, excelsior is commonly used as a packing material in the shipping of fragile items. A small handful of excelsior is pulled away from the rest, formed into a ball with your hands, and then stuck in the culture cup after the media has been added. Being a product made from wood excelsior can have some dust, which has left some people seeking alternative options for a substrate. One such option that is popular is coffee filters. A bouquet of several commercial-grade paper filters twisted together in the center and stuck into the culture cup creates adequate surface area.

     The preferred lid for which to use in fruit fly culture is the “Fabric Waffle” style. A “Pin Prick” style lid is also available, but these typically do poorly for fruit fly cultures. As the culture develops both the media as well as the flies themselves produce toxic carbon dioxide (CO2). CO2 is heavier than air, and will settle on the bottom of the culture. To avoid suffocating fly larvae will climb the sides of the cup, and even try to exit the culture. With Pin Prick lids larvae will try to crawl through the holes. After getting partway out of the hole the larvae will get stuck and die, blocking the hole. This will have a snowballing effect, which usually results in the total collapse of the fly culture. A second reason Pin Prick lids are not preferred is the risk of contamination from wild flying fruit flies. In theory a wild fruit fly could deposit eggs through the pin pricks with their ovipositor into the fly culture, resulting in flying fruit flies! It is good practice to write the date the culture was made, and what type of flies are inside, on the lid of each culture once inoculated. Pro-tip: Fruit fly larvae are nutritious and a great treat for dart frogs. They can be a critical tool when trying to fatten-up a fast growing frog or get pairs into breeding condition. Larval maggots are easily harvested by putting a solid lid on the culture cup. The quick buildup of CO2 will cause the maggots to leave the media and begin climbing the walls of the culture cup. From the sides of the cup the maggots can be easily scooped up with a small spoon or popsicle stick and placed on a leaf in front of the frogs. Best part is licking the spoon at the end!

A Fabric Waffle lid provides greater ventilation than Pin Prick style lids. Make sure to label your cultures. 

     Newly constructed fly culture cups (before being inoculated with starter flies) can be stored in the fridge for around a week, or the freezer for around a month, without ill effects. This enables the keeper to stagger the start date of cultures, and thus the date the cultures boom, without having to pull out all the fly culture components every time a culture is to be started. For example instead of making and starting 6 cultures all at once, you could make six cultures and start 2 of them, putting the remaining 4 cultures in the fridge. Two days later pull out and start another 2 cultures, and do the same with the last 2 cultures 2 days after that. This will provide a more consistent fly availability compared to the relative feast or famine resulting from if all the cultures were started on the same date. 

Fruit Fly Life Cycle

     To be able to understand the process of cultivating fruit flies their basic life cycle should be understood. This will also help in determining what stage various cultures are currently in so that harvests can be planned accordingly. The description and timelines below are for D. melanogaster. D. hydei are similar in sequence, but slightly delayed in time frame. Other notable differences between the two species will be mentioned where applicable.

     D. melanogaster eggs can not be seen by the naked eye, being about a half a millimeter in size. The eggs hatch about 12 hours after being laid. The larval maggot feeds and grows for about 4 days before pupating. The larval pupae undergoes metamorphosis for around another 4 days and then emerges in its adult form as a fly. The flies reach sexual maturity a mere 8-12 hours after emergence, and during their roughly 50 day lifespan females can lay several hundred eggs. These development times are based on their ideal culture temperature of around 76°F-78°F, and vary slightly at different temperatures.
Pro-tip: Strategic placement of the fly cultures can keep them at their ideal temperature. Placing the cultures above the lights of the vivarium, or even just on a shelf closer to the ceiling, will keep the cultures a few degrees above room temperature.

Fruit Fly eggs hatch into larval maggots which feed and grow over the course of a few days. Maggots have a high fat content, and when gut-loaded with a nutritious media can be a dietary asset for your frogs. 

     The time frames above support the fact that a fly culture will begin producing new flies roughly 9 days after it was made. This can be confirmed by the presence of virgin female flies whom display a light-colored translucent abdomen. Unless in desperate need of flies at that moment the harvesting of flies should be delayed until at least a day or two after first emergence. This will allow those first emerging flies to sexually mature and lay eggs themselves, which can result in a second wave in the number of flies the culture produces later on in the cultures lifespan.

The larval maggot will undergo metamorphosis, forming into chrysalis from which the adult fly will emerge. The dark chrysalises have flies ready to emerge. 

     Due to population dynamics and the life cycle described above a fruit fly culture will undergo a population boom. This exponential growth results in thousands of flies emerging overnight. This is commonly referred to as a “Booming Culture” or a “Producing Culture”. This critical point varies based on the particular environment in which the flies are being cultured. It is typically around day 11 or 12. Hydei cultures undergo a much more substantial boom than Melanogaster. In some instances such booming cultures may actually require the harvesting/removal of significant numbers of flies to prevent exceeding the carrying capacity of the fly culture resulting in its complete collapse.

This fruit fly culture has undergone a population boom.

     After a culture booms it will continue to produce flies for several more weeks, although the productive of the culture will decline in both the number of flies, and physical quality of the flies. This is due to the declining environment of the culture with time.
Pro-Tip: the smaller and more frail flies produced by a culture approaching a month in age make great prey items for new metamorphs and small frogs. They are a great stepping stone between springtails and regular fruit flies!

Fruit Fly cultures at several different stages of production. The ones at the top are newly made, while the bottom ones are at the end of their lifespan.

     While the fly culture will continue producing until the media is completely consumed, it should be standard practice to dispose of the culture after it reaches 4-5 weeks of age. This is a preventative measure to avoid the establishment of mites in your fly cultures. As with flies, the pest mites can also experience exponential population growth, and disposing of the the culture at 4-5 weeks of age prevents this from happening.

This fruit fly culture has used all of it’s media.

Disposing of Fly Cultures

     If at the time of disposal the fly culture does not have a burgeoning mite population and still has plenty of larvae you can place the culture on its side with the lid off in the dart frog vivarium. The resident frogs will pick off any larvae they can reach and any flies that emerge. Not only are fruit fly larvae great for bulking up fast-growing froglets or actively breeding pairs but the activity of hunting a fly culture is also an enrichment activity for the frogs. Cultures at the end of their life also serve as great vacation-feeders in times of need. However this feeding method should not be relied upon as part of the routine husbandry regime as any flies or larvae consumed lack a dusting of vitamins or minerals. The consistent dusting of the prey items with the proper supplements in a correct schedule is critical to the long term health of the dart frogs in captivity! More information on supplemental dusting of flies is discussed later. 

These Dendrobates tinctorius “Bakhuis” enjoy polishing off any strangling flies from old cultures.

     A fruit fly culture at the end of its life can be a smelly and disgusting thing that many people choose to simply throw away. Those who are environmentally concerned may wish to reduce the amount of plastic going into landfills. This can be accomplished by cleaning and reusing both the culture cups and/or the culture lids.

This Dendrobates tinctorius “Brazilian Yellow Head” makes sure no fly maggots go to waste!

     The fly culture cup with the spent media can be quite the task to clean, however there are some tips to make the process easier. Putting the cultures in the freezer to freeze the media and excelsior into a solid block can allow it all to be removed in one solid piece. Conversely putting the spent cultures outside to dry in the sun also makes the culture contents easier to remove effectively. After the cups are emptied they can be washed with dish soap and water.

     Compared to the culture cup the culture lids remain relatively clean during the culture process. They can be cleaned and sterilized by soaking them in a bucket of bleach water overnight, after which they are simply rinsed and dried. The bleach does all the hard work, virtually dissolving any organic waste. Bleach is a volatile compound that will evaporate, so once the lids are completely dry there is no bleach left. Just be sure to use regular Chlorine bleach, you do not want the “splash-less” or any scented variety. The fabric-waffle lids can be reused many times, but eventually the fabric will deteriorate and the plastic become brittle and crack, at which time they can be replaced.

How to Harvest

     Harvesting can begin a day or so after a culture begins producing new flies. Gathering flies from a culture can be tricky for the uninitiated, but with a little practice it becomes easy to do so without any escapees!

Pro-Tip: should you accidentally spill a cup full of fruit flies a vacuum is capable of quickly reigning them all in, be sure to keep one handy!

     Fruit flies at rest will be dispersed throughout the culture, but upon the disruption of the culture cup being picked up the flies will begin rapidly climbing to the top. Therefore before opening the lid of a culture cup it should first be gently slammed on the tabletop a few times. This will knock most of the flies to the bottom of the culture. During the time it takes them to climb back up to the rim of the culture cup (a mere second or two) you will open the lid of the culture and have it positioned to tap out flies into a harvesting container.

With practice flies can easily be harvested without any escapees.

     The harvesting container can be an empty 32oz culture cup, although new keepers may find it easier to accurately tap flies into a larger bowl. A small amount of vitamin and mineral supplement should be added to the harvesting container before the harvesting begins.

     When the culture cup is opened the lid does not have to be completely removed. You may find it easier to pry the lid open along the pouring-edge of the cup, while keeping the lid snapped onto the remainder of the rim, making it quicker to snap shut. With the lid opened you now tap the culture cup against the harvesting container so as to knock flies out of the culture cup and into the harvesting container.

Some people may find it easier to set the collection cup on a table, while others may find it easier to hold each cup in your hands.

     The flies in the harvesting container can be simultaneously dusted with the vitamin and mineral supplement powder as they fall into the cup in a simple tapping and swirling action. The flies are typically unable to climb the walls of a harvesting container once they are coated in a fine supplement powder. Once enough flies have been tapped into the harvesting container the lid of the culture cup can be snapped closed.

     With the lid back on the culture cup and the flies dusted in the harvesting container the harvest is now complete, hopefully with minimal escaped flies. This harvest process may be intimidating at first, but with the practice gained by regularly feeding your frogs it can be done quickly and without worry!

     The dusted fruit flies are now ready to be fed to the frogs. One method that can be employed when feeding frogs is a Feeding Station. A Feeding Station is usually a slice of fruit or a small cap filled with a food item for the flies. A slice of banana is my preferred item. The station is set in the vivarium and the flies are added on top of the station. Instead of immediately beginning to wander off the flies are attracted to the food and congregate around it, allowing easy pickings for the frogs. This ensures that the frogs are able to consume plenty of flies shortly after the are added, before the flies cleanse themselves of the supplement dust. If the feeding station is kept up (simply keeping adding a fresh slice of banana on top of the older partially consumed piece) the station will soon start producing nutritious maggots for the frogs as well! In large vivariums, or in cases when a dominant frogs claims a feeding station as their territory, multiple feeding stations can be used. A feeding station is a great tool, but not a requirement.


Once dusted with a supplement powder fruit flies have a hard time climbing the walls of the cup.


     After harvesting fruit flies it is important to wash your hands. This will cleanse your hands of any mites that have gotten on you and prevent you from spreading them. Mites, usually Grain Mites, are a pest that are commonly encountered by dart frog hobbyists. The mites find their way into fly cultures, and can reach problematic levels should efforts not be made to keep their populations in check. The mites do not pose a serious direct threat to the dart frogs, in fact some smaller dart frogs will consume them. However they could cause irritation stress should they establish themselves in the vivarium and crawl all over the frogs.

The large Dendrobates tinctorius “Citronella” wants flies, hold the mites.

     The dusting process preceding feeding fruit flies to the frogs helps prevent mites from entering the vivarium. The calcium or vitamin powder covers the flies surface making the mites unable to hold on. The mites fall off of the flies and into the excess powder at the bottom of the cup. This leftover supplement powder should not be added to the vivarium with all the flies. The flies can be separated from the powder by gentle tapping of the cup while pouring out the flies. The flies pour out of the cup faster than the powder, and with practice the flies can be perfectly separated from the excess mite-ridden powder.

     The placing of outdated fruit fly cultures into the vivarium before they are disposed of (as discussed above) is a direct way of introducing mites into the vivarium. This is usually not a problem as any small populations of mites will get picked off by the frogs or disperse into unnoticeable populations in the substrate. However a fly culture contaminated with large numbers of mites can cause issues if added to the vivarium. If this happens a close look will reveal the glass and rim, including the OUTSIDE of the vivarium, covered in tiny mites! If this happens dispose of the fruit fly culture immediately, and wash your hands! All the outside glass and surfaces of the vivarium and surroundings can be wiped down with isopropyl alcohol. The alcohol will kill and remove the mites, drying quickly leaving no residue.

     Being able to keep frogs for years without ever running into problems with mites is a rarity. However practicing good protocols in place concerning fruit flies can prevent them from ever becoming a serious issue. In addition to those already mention above some additional ways to win against mites involve the keeping and placement of the fruit fly cultures. Population explosions of mites happen within the fly culture itself, preventing this from spreading anywhere is important. On the converse, preventing anything from getting into the cultures is equally as important. Analyzing both of these issues will help immensely with the bio security of the cultures.

     Whether it be an island in the middle of the ocean or a castle surrounded by a deep moat; water is an obstacle as old as time. Unlike beneficial springtails Mites do not float, and they can not swim. Therefore keeping the fly cultures sitting in a shallow tray of water, without touching each other, will prevent mites from walking from one culture to another.

     Diatomaceous Earth (DE) is a white powder made from the fossilized remains of micro algae know as diatoms. While appearing as a soft powder to the naked eye on a microscopic level it is very sharp and abrasive. This has allowed it to be used as a mechanical, chemical-free, insecticide. A shallow layer of it will kill any mite that dares to traverse it. The disadvantages of DE Powder is that it being a fine powder it can easily be wafted into the air, and it should not be inhaled due to its abrasive nature.

Diatomaceous Earth powder creates a impassable barrier that can prevent mites from spreading among cultures.

     A third option to keep fly cultures bio secure is with chemicals. Mite Paper is a convenient product which can be laid upon a shelf upon which cultures can be sat. Besides the use of chemicals the disadvantage of mite paper is that it is only effective for a few months until it needs to be replaced, the cost of which can add up over time. A slightly cheaper method would be to line the shelf with a strip of paper towels, onto which a Mite Spray can be sprayed.

     A final yet simple effort that can be taken in order to prevent mites from spreading is to keep older producing cultures in a different area than newly made and not yet producing cultures.


     While cultured fruit flies are an easily cultured prey item for captive dart frogs they do not provide all the nutrients that the frogs require for a full healthy life. This is accomplished by dusting the fruit flies with powdered supplements.

     One of the most important nutrients that must be supplemented is Calcium. There are many calcium supplements made for reptiles and amphibians, and they can differ in several ways. One of the most important differences is in the amount of Vitamin D3 they contain. The levels of this Vitamin reptiles and amphibians needs varies based on the environments they come from and other ways besides ingestion (such as basking under UV-B light) they may acquire it. Making sure that the calcium supplement you use was designed for frogs is important. Rephasy Calcium Plus is a preferred choice. Every feeding of your frogs should be dusted with a supplement. Calcium is the default supplement powder that should be used in all feedings in which one of the below supplements are not used. For example if the frogs are fed every day then 4-5 of the feedings per week should be dusted with calcium.

     Besides calcium a very important vitamin for dart frogs is vitamin A. Deficiencies in vitamin A can result in a multitude of different ailments. These include Short/Sticky Tongue Syndrome (STS) which inhibits the frog from consuming prey properly, as well as decreased egg quality resulting in diminished fecundity in frogs of breeding age. Vitamin A should be supplemented every 2 to 3 weeks in all frogs, and can be supplemented even more often in actively breeding frogs, especially if poor egg quality is observed. Rephasy Vit A Plus is a good option.

     A good multivitamin can also be added the the supplement routine of dart frogs. Dusting a meal every one or two weeks can help prevent the frogs from becoming vitamin deficient. A good option for such a multivitamin is Rephasy SuperVite.

     Another supplement that can be added to your frogs diet is carotenoids. Not only do they provide vitamin precursors but they are also widely used in the diets of captive animals to increase the red and orange coloration. It’s how we keep flamingos pink! Lack of carotenoids in captive animals diets can result in dull or washed out colors. Astaxanthin is widely used in fish aquaculture as well. Rephasy SuperPig contains an assortment of carotenoids, a dusting of flies once a week will keep your frogs vibrant!

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