Four Degrees and a Plastic Box: Brumation Substrate for Salamanders

The fridge sits at 4.2 C, the box has been in there since the first week of December, and the animal inside has lost 6 percent of its body weight in nine weeks. That is a good outcome. The box next to it, set up the same day by the same keeper, lost 19 percent, because the moss in it was bone dry and nobody weighed anything until February.

Brumation is the part of salamander keeping where substrate matters most and gets discussed least. Eight to twelve weeks in a cold box is a long time for an animal that cannot drink, cannot eat, and depends entirely on the moisture you put in before you closed the lid.

Moisture by Feel, Not by Pour

The target is damp moss that holds together when squeezed and releases no water. Not dripping, not dry enough to crumble. In practice that is about three parts water to one part dry moss by weight, mixed and left to equalise for an hour before the animal goes in.

A thin layer of hydrated polymer under the moss helps hold that moisture steady, but it must not be in contact with the animal. Two centimetres of moss over a 1 cm gel layer, with a barrier of mesh or gravel between, gives you a reservoir without a wet surface. Skip the reservoir and you will be opening the box to mist it in January, which wakes the animal and defeats the purpose.

The Box That Dripped on Their Backs

The classic failure is a box that is too wet. Condensation forms on the lid, runs to the edges, and drips onto the animals for weeks. Two fire salamanders came out of a box like that with skin lesions along the spine and one with a swollen toe, and the keeper had done nothing but follow advice to keep it moist.

The fix is a lid with ventilation holes and a layer of dry paper or moss against the inside of the lid to absorb condensation before it drips. A box with no holes and wet moss is a rain chamber, not a brumation chamber.

The opposite failure is quieter. A box that is too dry produces steady weight loss with no visible sign until the animal is thin. By the time you notice, you have lost most of the window and the animal is going into spring with no reserves.

• Weigh every animal before it goes in, at week four, and at week eight.
• More than 10 percent loss means the box is too dry or too warm; correct it, do not wait.
• Ventilation holes on two sides, covered with fine mesh so nothing escapes.
• No food for seven to ten days before the box goes cold, so nothing rots inside.

Checks, Weigh-Ins and the Exit

Open the box once a week, in a cold room, for no more than a minute. Check moisture by touching the moss at one corner, check the animal is alert enough to move, and close it. Do not mist inside the box; if it needs water, replace a corner of the moss with fresh damp moss and remove the old piece.

Coming out is the riskiest week. Bring the box to 10 C over two days, then 15 C, then into the permanent setup. Offer water before food. A salamander that eats on day one after eight weeks at 4 C usually regurgitates it, and the substrate gets the blame for a problem that was timing.

What to Write on the Lid

Date in, start weight, target weight at week four, and the moisture mix you used. Four lines of marker on a plastic lid is the whole system, and it is the difference between a brumation you can repeat and one you survive.

Before the next animal goes into the fridge, put it on a scale and write the number on the lid. Everything else in this article is easier to get right once you have a baseline.