All living things on the surface of the planet are exposed to ultraviolet light to some extent. Diffused and reflected UVB will penetrate into deep shade and even nocturnal creatures may be exposed to small amounts whilst hidden in their daytime retreats. Exposure to UVB allows tree frogs to synthesize vitamin D in their skin, which is vital for their proper health.
In general, captive tree frogs benefit from UVB light that mimics the level of UV exposure they would get in the wild. Many tree frog species are nocturnal and some live in thick forests where much of the UVB is filtered by the forest canopy. Still, even these will benefit from low levels of UVB.
That said, it’s important to note that many tree frog species can survive without UVB lighting, as long as they are fed gut-loaded nutritious food, dusted with high-quality calcium and vitamin supplements. Their diet can give them sufficient amounts of Vitamin D3 to absorb dietary calcium.
In fact, many species of tree frogs have been raised and bred in captivity, living a long life in the absence of UVB light – which proves that UVB is not strictly essential for all tree frog species
However, other species can suffer from metabolic bone disease (MBD) when not provided with adequate UVB – even when fed gut-loaded crickets dusted with vitamin/mineral powder.
In short, UVB lighting is an absolute essential for some tree frog species – but it is generally beneficial to almost all tree frog species at the right intensity (even for species that do not strictly need UVB).
Understanding UV light
All of the energy from the sun that reaches the earth arrives as solar radiation. This solar radiation is transmitted in waves or particles at different wavelengths and frequencies – known as the electromagnetic spectrum.
The spectrum is generally divided into radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays, and gamma-rays.
Ultraviolet (UV) light has shorter wavelengths than visible light, which makes it invisible to the naked eye.
It is commonly subdivided into ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC), based on their wavelengths.
All of the UVC and most of the UVB radiation (about 95%) is absorbed by the earth’s ozone layer, so nearly all of the ultraviolet radiation received on Earth is UVA.
Amphibians need both UVB and UVA light from the sun to live healthy lifestyles but do not need UVC.
- UVA light helps regulate behaviors such as feeding, diurnal movement, mating, and similar activities. Frogs will generally have a positive response if exposed to UVA light. Increased reproductive behavior, feeding, and activity levels can often be seen.
- UVB light allows frogs to synthesize vitamin D3 inside their skin. Vitamin D3 helps the frog to absorb calcium in the gastrointestinal tract, which is crucial for bone structure and growth.
- UVC light is not required for amphibians, and at high levels, it can be harmful to most animals.
Only the sun can provide all the radiation wavelengths necessary for amphibian metabolism from a single source.
However, in captivity, it’s recommended to somewhat replicate this through a variety of different types of artificial light sources.
UVB For Captive Frogs
UVB plays an important role in the vitamin D3 metabolism of captive frogs. Vitamin D3 allows calcium to be absorbed from the gastrointestinal tract, as well as having other important functions.
Vitamin D3 deficiency in frogs can lead to low calcium levels which can result in bone density issues, poor digestive tract motility, muscle weakness, reduced immune system, and neurological symptoms such as twitching and seizures.
One of the most common conditions is called metabolic bone disease (MBD) where the bones lose their calcium stores and become very weak and rubbery.
Do All Pet Tree Frogs Need UVB?
In general, captive tree frogs will benefit from a UVB light that mimics the level of UVB exposure they would get in the wild.
Some species may have very low or no requirements for UV-B and, others may have very high requirements.
A lot of tree frog species are nocturnal, and/or live in thick forested areas where much of the direct sunlight is absorbed by the foliage, or filtered by the forest canopy.
However, even these receive small amounts of diffused and reflected UVB, penetrating between leaves, and other plants – which plays a role in their health and well-being.
Many arboreal tree frog species live and sleep high up in the dense forest canopy, where they are exposed to moderate amounts of sunlight.
Some tree frog species such as the American green tree frog (Hyla cinerea), prefer to live in open-canopy forests, and they are exposed to considerable amounts of sunlight in these habitats.
Non-arboreal tree frogs that live in forested areas are also exposed to solar radiation throughout the day in light gaps, and sunflecks under forest canopies.
Many Tree Frog Species Can Survive Without UVB Lighting
Some tree frog species have adapted to be able to live in areas where they are not exposed to much UVB.
In captivity, many of these tree frog species can be kept and bred successfully with no access to UVB, provided that adequate levels of vitamin D3 are provided in the diet.
These are mainly insectivorous species which might be expected, in nature, to obtain a considerable proportion of their vitamin D3 from their diet.
A few tree frog species are proven to be able to survive and stay healthy without UVB lighting include:
- Red-eyed tree frog (Agalychnis callidryas)
- Amazon milk frog (Trachycephalus resinifictrix)
- Gray tree frog (Hyla versicolor)
- White’s tree frog (Ranoidea caerulea)
- American green tree frog (Hyla cinerea)
- Vietnamese mossy frog (Theloderma corticale)
Even though these tree frogs can survive without UVB, they may still benefit from the ability to experience at least some gentle UVB during daylight hours.
The Provision of UVB May Improve Growth and Skeletal Development in Some Frog Species
Researchers studied the effects of UVB radiation on the growth and skeletal development of the Amazon milk frog (Trachycephalus resinifictrix).
They found that frogs provided with daily UVB treatment showed improved growth, condition, and skeletal calcification compared to those with intermittent or no provision of UVB.
All the frogs in the experiment were fed a standard feeder cricket diet that provided minerals including calcium and vitamins including vitamin D3.
However, the frogs provided with UVB still showed greater skeletal calcification when compared to the frogs without UVB.
The improved growth of the frogs on the UV treatment suggests that UVB provided increased calcium metabolism to that provided by a standard dietary intake of vitamin D3.
This could be due to UV-B synthesizing amounts of vitamin D3 lacking in the diet or to a basic metabolic requirement for UV-B to provide for calcium metabolism.
Can You Just Put Your Tree Frog Next to a Window?
The best and most balanced source of ultraviolet light is, naturally, the sun. However, UVB cannot pass through normal glass, so placing an indoor tree frog near a window will not supply them with the UVB they need – but it can provide a regular day and night cycle.
Frogs housed indoors need to be provided artificial UVB light by the use of special bulbs specifically designed for reptiles & amphibians.
How to Provide UVB Light
UVB can be provided by several types of lights. Some of these produce large amounts of UV-B along with a large amount of heat. These are mainly used for reptiles.
However, there are also lower-output UVB bulbs available – these are generally preferred for most amphibians.
In the United States, UVB bulbs are generally available in 2.0, 5.0, and 10.0.
2.0 or 5.0 UVB bulbs that run fairly cool will work well for most tree frogs.
The UVB bulb should be housed in a reflective fixture, and the frog should not be able to get too close to the lamp.
Remember to provide a few places your frog can hide in to escape from the light. You can do this by placing branches or plants in a way to provides shaded areas.
UVB bulbs should be used during the day and turned off during the night to mimic daytime and nighttime.
Every type of frog has slightly different needs but a general rule of thumb is to keep the UVB light on for 12 – 14 hours and off for 10 – 12 hours.
UVB Bulbs Degrade Over Time
It’s important to note that all UVB sources degrade over time. As the bulb degrades, visible light output can remain the same – but UVB production will slowly begin to drop off as soon as the bulb is turned on.
UVB bulbs have a coating inside the glass that allows them to emit UVB lighting. This coating wears off over time and the bulb will stop producing the UVB your frog needs.
At this point, the bulb will serve no other purpose than providing visible light and must be replaced for the continued health and well-being of your pet.
The rate at which bulbs degrade depends greatly on the type of bulb, and how long the bulb is being used per day.
In general,
- Linear and compact fluorescent bulbs will need to be replaced about every 6 months
- Mercury Vapor bulbs will typically last 1 year with a wire ballast
- Metal Halide bulbs can last up to 2 years
It’s a good idea to monitor the UV output of your bulb with a UV meter. A great one that is popular among many reptile and amphibian hobbyists is the UVB meter sold by Solartech under the brand name “Solarmeter 6.2.”
If you opt to go without a UVB meter, you should consider replacing the bulbs within the time frames recommended by the manufacturer.
UVB Effectiveness and Blocking
As the distance between the UVB bulb and your pet increases, the usable UVB radiation decreases rapidly. Most bulbs provide UV levels and readings at a recommended minimum distance from the bulb.
Make sure to consult the specific manufacturer’s recommendation often found on packaging material, or in a manual or guide found in the box.
In addition, glass and acrylic (also known as Plexiglass) block UVB rays, so if there is any glass or acrylic between your UVB source, and your pet – the pet will not receive any benefit from the UVB bulb.
Also, a screen lid can significantly reduce the amount of UVB available to your frog. In general, the closer or more dense the mesh, the less UVB passes through the screen. It’s a good idea to use as large a mesh size as possible when selecting a screen top for your pet.
When most UVB sources report their UVB output at a certain distance, this reading is often taken with no obstructions between the bulb and the UVB meter.
Can Frogs Receive Too Much UVB?
Excessively high doses of UVB radiation can be harmful, or even lethal to most frog species. This can happen from prolonged exposure to UVB, incorrectly installed UVB light sources or use of UVB light sources with too high an intensity.
It is well-known that in mammals, excessive exposure to the sun’s ultraviolet rays – or their artificially produced equivalent – can be harmful. The situation in amphibians has not been studied in detail but is almost certain to be similar.
Although the UV output from many lamps sold for reptile and amphibian use is only a fraction of that found in natural sunshine, all artificial sources of UV radiation must be treated with respect.
Some UV lamps emit very high UV radiation at close range, so the manufacturers’ recommended minimum distances should always be taken seriously.
Also, some UVB bulbs produce both heat and UVB, so a hot light fixture can be harmful if placed in a small enclosure, or even in a larger enclosure if your frog gets too close.
It is VERY IMPORTANT to ensure that your pet frogs are not exposed to levels of UVB which would be unnaturally high for a wild animal of that species in its normal habitat.
In addition, you should always provide a few places your frog can hide and move out of the effective range of its UVB light.
Extra UVB above the requirement for D3 production is of no benefit.
Photo credit: Fungus Guy (CC BY-SA 4.0).
Sources:
Kats LB, Bucciarelli GM, Schlais DE, Blaustein AR, Han BA (2012) Ultraviolet Radiation Influences Perch Selection by a Neotropical Poison-Dart Frog. PLoS ONE 7(12): e51364. https://doi.org/10.1371/journal.pone.0051364
Dr. Robert Browne, Dr. Francis Vercammen, and Rachael E. Antwis (2009). UV-B, Vitamin D3, and amphibian health and behavior (PDF).
National Aeronautics and Space Administration, Science Mission Directorate. (2010). Ultraviolet Waves. Retrieved [June 11, 2023], from NASA Science website: http://science.nasa.gov/ems/10_ultravioletwaves
Elfi Verschooren, Robert K. Brown, Francis Vercammen, and Jeffrey Pereboom (2013). Ultraviolet B radiation (UV-B) and the growth and skeletal development of the Amazonian milk frog (Trachycephalus resinifictrix) from metamorphosis. Global Journal of Anatomy and Physiology.
