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Overwintering Amphibians

Last Updated: 3/14/16

Helping Frogs and Toads to Overwinter
Frogs Dying in Early Spring
Chytrid Fungus
Overwintering Frogs Indoors

For more on winter, see my winterizing page.

Helping Frogs and Toads to Overwinter

Hibernation for Aquatic Frogs:

A common problem for pond keepers is overwintering frogs. Most aquatic frogs overwinter inside ponds whereas toads and some frogs overwinter in dirt outside of the pond. Frogs that overwinter in the water include bullfrogs, green frogs, and pickerel frogs. Often tadpoles are bought, turn into frogs, but die over the pond's first winter in climates where the pond freezes. To increase the likelihood of frogs surviving the winter, a few things can be done. First, as with fish, the pond should not freeze over completely. With a few rare exceptions, if the frog freezes, it dies. Also, keeping a hole open in the ice using a de-icer, aerator, or waterfall allows gas exchange to occur. They may seem dead but frogs are breathing very slowly through their skin while submerged over winter. They can suffer from oxygen depletion in an iced-over pond just as can the fish.

Frogs sometimes bury themselves in dirt and muck in the bottom of a pond but not as deeply as an aquatic turtle. They cannot bury too deeply too long, or they will suffocate. Therefore, it is somewhat advantageous to leave some debris on the bottom of the pond. If the pond is too "clean," then the addition of a container of sand or soil can provide a home for the frogs. Putting clay soil or sand in a cat litter pan and sinking it to the bottom is one possibility. That can be quite messy. Frogs will also dig in to plant pots. My green frogs and bullfrogs often do not bury at all but just sit on the liner among the leaves. A few leaves can be left on the bottom so that the frogs can sleep under them. Finally, to reduce the chances of frogs being eaten over winter, be sure to provide lots of hiding places as with the fish.

Over winter, frogs often turn dark and mushy and look dead. Their color tends to match that of rotting leaves on the bottom. On warmer winter days, they may move around a bit at the bottom. Often, they will not respond to stimulation (much). Do not disturb them unless fungus is seen growing on the frog, or the frog is degrading which are signs that it is in fact dead. Dead frogs are often upside down with their tongues hanging out. A predator such as a raccoon, heron, or a large fish would have no problem eating an overwintering frog since they are very slow. Hiding spots can include clay pots and PVC pipe. Most plants have died back over winter and provide little protection. Their pots of course do provide a convenient place in which to settle.

Someone asked me if frogs hibernate with their eyes open. Well, my frogs appear to hibernate with their eyes shut so that would be normal. Frogs that die often also have their eyes shut (if sealed by yucky stuff) but they may be open as well. A hibernating frog should still respond to touch somewhat. If you are not sure, remove the frog. Smell it. Look for mush or fungus. If the frog stinks, is mushy, and does not move, it is dead. If it just died, it may be hard to tell. You can slowly warm it up to room temperature inside. If it does not "wake up" shortly after being warmed, it is dead. Anyway, I hope you do not find any dead frogs!! There is a photo of one lady's hibernating frogs at http://mywebpages.comcast.net/yurgen/frogs.html. It looks like one green frog at the top and two large bullfrogs. The photo link was posted to rec.ponds on 12/14/02.

I was asked on 11/3/03 by Ronna at what temperature my green frogs stop being active. I would say it is the same as the fish, about 50-55 degrees F when they no longer come out of the water. If the air temperature is 55 or above, even if the water is a few degrees cooler, they sometimes still come out to sun on warm fall days. If there is a warm stretch even in winter, they may come out. They are slower and look yuckier as far as consistency and color, being more brownish black than their summer time green and vibrant colors. Above 60 degrees and the frogs come out for sure. In the fall, the bullfrogs, green frogs, and pickerel frogs often get on top of the nets and bounce around. I have a section on that below.

Here is an article I wrote for Organic Gardening that includes a section on overwintering aquatic frogs indoors.

Hibernation for Toads and Terrestrial Frogs:

Terrestrial toads hibernate by burying below the frost line. Providing lots of areas with leaf litter, logs, and moist dirt will help toads hibernate. Terrestrial frogs such as spring peepers and wood frogs, hibernate in cracks among rocks and logs or among leaf litter. Since these locations freeze, so do the frogs who have a natural antifreeze in their bodies. Providing piles of rocks, logs, and leaves can help terrestrial frogs hibernate. Also, leave some dead trees and fallen logs around.

For more information on winterizing ponds, visit my pond winterizing page.

For a short discussion on frogs overwintering, see my December 2005 pond newsletter.

Frogs Dying in Early Spring

There seems to be a common problem in ponds with aquatic frogs where they die right about the time that the ice melts in the ponds of colder regions. In Maryland, this happens in my ponds in late February. Frogs that die this time of year are found upside down on the bottom of the liner. Their tongues are usually hanging out and drained of color. Sometimes the tongues are wrapped around their heads. The skin is usually slothing off with patches of whitish foggy skin. The frogs are drained of their normal color but this is perfectly normal for a hibernating frog (to blend in with the muck on the bottom of the pond). Each year, I normally lose a few frogs this way but in the spring of 2000, I fished out over a dozen such victims. In February and March of 2001, I removed about a dozen dead frogs, and few live frogs were seen. Frogs often die over winter if the pond freezes over completely. Toxic gases build up under the ice and fresh oxygen cannot get in. The frogs and fish suffocate.

My pond retained openings due to a de-icer and waterfall plus my fish were fine so I know this is not what happened to my frogs. My pond has enough leaves in the bottom, pots, etc. for the frogs to root into to hibernate so that was not the problem either. When I asked the newsgroup rec.ponds about this, I got a number of replies. Some people pointed out that amphibians are facing declines in populations and deformities throughout the world. This is very true but I do not think it has to much to do with my particular problem. Then, someone mentioned that since 1999 was a record drought year, the frogs may not have obtained enough insects to eat before hibernation. When the water warmed up, the frogs were simply empty of food reserves. All the frogs did appear emaciated so this makes sense to me. I did hand feed a few frogs a few times in the summer of 1999, and they were especially hungry. There were few insects around. Let me know if you have any other ideas.

On 3/22/00, I found two dead green frog tadpoles as well and began to find a few more in 2000. Perhaps my green frogs (adults and tadpoles) have been targeted by some amphibian disease or parasite. The wood frogs seemed unaffected as they laid eggs in 2000. Of course, they overwintered outside of the pond. In March of 2001, again a dozen or so dead green frogs and green frog tadpoles were removed from my ponds. The fish and wood frogs experienced no losses.

Frogs in my 153 gallon pond:

I cleaned out my 153 gallon pond on 3/26/01. There were 8 dead green frogs, 2 dead pickerel frogs, a few dead tadpoles, and 2 dead trapdoor snails. Three live green frogs and two live female wood frogs were found as well as hundreds of ramshorn snails and green frog tadpoles and 19 fish. The pond is deep (2 feet) but narrow (just a few feet) so I would bet that oxygen depletion over winter was a factor. The pond has a de-icer but I kept switching half a dozen of them in and out as the de-icers would stop working and freeze in quite often. The next year, I planned to put an air stone in to this pond over winter so that, hopefully, no more frogs would suffocate! On 11/10/01, when I removed the filter for the winter and added the de-icer, I did add an air stone, powered by a Luft pump. I hope it does the job!

Note: The Tetra Luft pump is a must-have pond supply but they no longer make it! There are very expensive larger aeration systems that are just too big for ornamental ponds. One possible replacement for this system might be the OASE pond-air aeration pump which costs about $53 in 2002. Two places that sell it are Aqua-Mart and Drs. Foster and Smith Aquatics. I got one, and it is not what I thought. It sucks air off the surface and mixes it in the pump and spews it out. It does not look like it would work in freezing temperatures but I will use mine to add oxygen to my large pond in summer only. I used it for one year, and it died. Guess what! Now, I see that Drs. Foster and Smith Aquatics carries the Luft pump in their aquarium catalog! It does not contain the outdoor cover but it looks like the same one! You could cover it with a plastic storage box or something. I bought one on 1/25/05 and found out that it is a Coralife Luft pump and not a Tetra Luft pump so it is different but looks like it should work the same.

Good news! On 3/29/02, I cleaned out the 153 gallon pond and found NOT ONE DEAD FROG! So, the air stone must have worked! I did remove a dead pickerel frog from my 1800 gallon pond that year but that is it! I found 13 live frogs in the 153 gallon pond. They were all green frogs. The wood frogs did not come to breed that year (probably due to the drought and fluctuating temperatures). Only 7 live fish remained in this pond so the tadpoles, frogs, and snails mostly had it to themselves! Here is a photo of the frogs waiting in a pot while I cleaned the pond. You can see heads from six of them.

Bad news in 2003. When I cleaned the 153 gallon pond, I found one scrawny young green frog, a female wood frog (who had laid eggs the week before), two green frog leg bones, and one green frog vertebrae, and that was all the signs of frogs. The pond still had hundreds of green frog tadpoles but something happened to the green frogs so that they never made it to overwinter (if they had, they would be dead or the bodies still in the bottom, at least partially intact). I think the worst drought in 100 years cut so far back on the insect prey available that they must have starved to death. I hope it does not mean that some predator has learned how to kill them efficiently or the tadpoles will not stand a chance when they come out as frogs. I miss them so much! Check out my page on green frogs and my spring 2003 newsletters for more information. On 4/30/03, I found my last adult male green frog; all that was left was his head, feet, and spine. The rest was bitten off obviously. Maybe the bullfrog did it or the raccoon. There are maybe two small green frogs left, that's it except for the tadpoles.

Update 2010: The frog populations all continue to rise and fall. In 2010, there are just a few adult green frogs, some babies, and the only bullfrog (a female) vanished in May. Luckily, the green frogs have laid plenty of eggs. I think the ponds are getting heavy predation from the great blue herons, hawks, and raccoons.

Every year, especially over the winter, I lose a number of frogs. The pickerel frogs especially have a high winter/early spring mortality. Some of the deaths may be due to Chytrid fungus but there is no way to know the cause of any individual's death by just looking at them.

Chytrid Fungus

During the summer of 2000, a large percentage of my previous year's tadpoles died during metamorphosis. Through a message on the newsgroup, rec.ponds, I became aware of a new fungus (at that time) that was occurring in the US and specifically in my state of Maryland. It is the chytrid fungus. I am not sure if that is what my frogs and tadpoles had/have. It is said to be carried by tadpoles and only strike them when metamorphosing. It gets frogs at any time which fits what happened to my frogs. All frogs and changing tadpoles that died had some sloughing, white skin. By 2010, chytrid fungus is widespread and a major problem for most amphibians. Without autopsies, it is impossible to say how many of the frogs that I have lost had this disease.

Chytrid fungus links:
Chytrid fungus
Chytrid fungus

Overwintering Frogs and Toads Indoors

Sorry if this section is a little confusing.

Aquatic Frogs with No Place to Go:

I am adding this section due to a number of people asking about what to do with frogs over winter if they cannot live outside. This may be the case if the outdoor ponds are too shallow, the frog has been a pet, the person has moved, etc. There are a few options.

1. Hope the frog leaves and finds a deeper pond. Such a pond must not freeze at the bottom, be in good condition, and preferably have an opening in the ice over winter.

2. Move the frog to a more adequate pond.

3. Bring the frog indoors and hibernate it. The advantage of this is that it more closely matches nature and requires little work.

4. Bring the frog indoors and keep it warm, active, and fed all winter. The advantage is that you can monitor and enjoy the frog. While mortality this way may be lower, hibernation normally extends the lives of those animals that hibernate and better prepares them for the breeding triggers of spring.

Be sure to identify the frog to be sure it is an aquatic hibernator. Bullfrogs, green frogs, and pickerel frogs hibernate under water. If the frog is a tree frog, spring peeper, wood frog, leopard frog, or other terrestrial frog, it hibernates on land, behind bark, around trees, or under the ground. Toads also hibernate on land.

Hibernation Indoors for Aquatic Frogs:

Keep an aquarium or indoor pond (any non-toxic container; Rubbermaid or Sterilite storage containers work well) in a cool area such as a garage, shed, or basement where the temperature is preferably between 35 and 45 degrees F. Fill the container half full of water. If it is cool, the frogs will just stay in the bottom. Land areas are not needed while aquatic frogs are overwintering but no harm would come if they were provided. Do not feed. For cover, a few leaves suffice. Adding dirt or sand will just make a mess. Keep the area out of direct sunlight. Put a net or lid over the container but be sure there is good ventilation. If desired, very light aeration will help ensure there is enough oxygen for the frogs. Strong filtration or heavy water movement will disturb the frogs. If kept between 45 degrees and 55 degrees F for a long period of time, the frogs will be active enough to burn off calories but not warm enough to eat so they may starve. If no cold room is available, then the frog should be kept active and warm (at or above 60 degrees F) as in the next section.

Keeping Aquatic Frogs Indoors and Active During the Winter:

A setup for an aquatic frog indoors over winter that is to be kept active is basically either a terrarium or an indoor pond. Be sure to include a lid or net on the top, ventilation, filtration, and some indirect sunlight. Frogs only eat live foods such as insects, snails, spiders, or worms. The easiest foods to buy include crickets, mealworms, and earthworms. Aquatic frogs need both water and land areas. They will use the water more so two-thirds water to one-third land makes sense. They will enjoy a shallow water area where they can stand in the shallow water with their heads easily out without having to do any work. Ideally, the water would be kept in the 60 to 75 degree F range. The warmer it is, the more the frogs eat and the more maintenance is needed including water changes.

Hibernation Indoors for Terrestrial Frogs and Toads:

These animals hibernate on land. They can either be hibernated or kept active. To hibernate them, put them in a secure container such as an aquarium or plastic storage container with a lid with ventilation holes. Keep them in a cool area such as a garage, shed, or basement where the temperature is preferably between 35 and 45 degrees F. Fill the bottom with about half a foot of leaves, twigs, etc. For tree frogs, add some bark or pieces of wood as well. The animals will bury into it and wait. Do not feed. To provide appropriate moisture, there are a few options. Into the substrate can be mixed damp sphagnum moss. Wet paper towels that are partially squeezed dry can be placed into the container and changed every few days. A small dish of water can be put into the setup. The setup may be misted on occasion. Toads do not need much moisture but terrestrial frogs need more. You have to balance their need to stay moist with the desire to prevent the growth of molds and other yucky stuff that likes moisture.

Keeping Terrestrial Frogs and Toads Indoors and Active During the Winter:

Set the animals up in a secure aquarium. Keep them at 60 to 75 degrees F. Frogs and toads only eat live foods such as insects, snails, spiders, or worms. The easiest foods to buy include crickets, mealworms, and earthworms. For the smaller animals, try wingless fruitflies too. Provide a small dish of water for them to drink. For substrate, reptile bark, sphagnum moss, leaves, etc. may work. Dirt is usually messy.

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