On Keeping Hermit Crabs Warm

written by Jenn Borgeson, Vanessa Pike-Russell, Crab Lover Don 1999 on our Hermit Crab Yahoo! Group.

Due to the date when this discussion takes place you will notice some of the information is no longer in line with current care. However, there is other useful information in the articles and well as benefit to retaining our historical data.

A very simple and relatively inexpensive way to insulate your tank is with reflective insulation. You can wrap your entire tank (outer walls) to retain heat during winter months or power outages.

Check out some other suggestions that have been made over the years.

Hints on keeping your hermit crabs warm by Hermies Yahoo!Groups Members

Jenn on Insulation:

Make sure your crab tank is in a naturally warm part of the house but NOT near a heater or heating vent … I keep my small 3 gallon plastic molting tank on the kitchen counter. Kitchens are naturally one of the warmer more humid places in your house. Also check out your bathroom or laundry room, but watch the temp … you don’t want them to get TOO warm.

You can also make a Crab-gloo very cheaply using foam board from your local craft or drug/groocery store. The board usually runs no more than $2 per poster board sized piece. Two pieces should do the trick depending on the size of your crab tank. To do this measure the height, the front (width) and the side (depth) … Add 1″ to each of these measure ments. Lets say your tank is 12″ high, 14″ wide and 8″ deep … so you will cut out 3 pieces that measure 13″ by 15″ (your crab-gloo back/top/front) and two pieces that measure 13″ by 9″(the sides) … With me so far? Good!

Now break out the duct tape … you will need to tape the sides on at 90 degree angles to the back. Now tape the top on to just one sides … this will work like a hinge and your can open and shut it to get into your tank. Place your 3 sided box over your hermie tank. The front piece is kind of optional … you can leave it loose and just set it in place at night to help keep your hermies toasty … or a good idea would be to tape it on just one side ( like the top to create a door … open it during the day, close it at night!
Your parents should not complain about this at all because you have just followed a plan and done geometry in the process! If you want to toss in some art … how about drawing and coloring background scenes on your foam board for your hermie friends to enjoy?! My kids to this on a regular basis with construction paper … sometimes they are at the beach, the mountains, school … it’s really up to YOU!

Keeping them Warm, by CLD:


The IDEAL temperature for your hermit crabs is around seventy-four degrees F. They are most content at this temperature, this is the night time temperature in their native land. Remember that this is the temp that you are trying to achieve at the substrate level….after all, isn’t this the level that they spend most of their time!!?? Keeping the tank between that 70 to 80 degree temp is what you are aiming for… Be sure to keep your thermometer at substrate level, since that is where they spend all their time and heat rises so true temperature would be difficult to obtain from a thermometer placed in the upper tank region.

If the temperature gets too low(50-60 degrees F), dormancy and hibernation will occur. A long hibernation may permanently affect the hermit crab. They don’t actually die unless the temp gets REALLY low (below 50 degrees F). However, when a crab gets too hot(a brown liquid discharge is an ‘overheat’ indicator), it causes irreversible damage and a usually quite painful death. Getting over 80 degrees is playing with fire. They may also hang out of it’s shell, be inactive, spend extra time in the water dish, or dig a lot to find cooler temperatures. Be sure to keep the temperature from fluctuating as this may cause stress.


The tank should also be kept between 50-60% exact humidity level (76-82% relative humidity, sometimes a gauge will measure in relative but most of the time they measure exact). If the air is too moist your crabs will have a hard time breathing. Bacteria, molds, and other harmful stuff will grow in the tank as well causing sickness and stress. A good way of knowing this if you don’t have a humidity gauge is if there is condensation on the sides. If the air is too dry their gills will dry out and they will slowly suffocate. Their gills need to be moist for them to breathe properly, this one reason why lightly misting them once a day is encouraged. Be sure to keep the humidity from fluctuating as well because this may cause stress.


There are two different types of heating equipment you can use…

A Moonglow Bulb- A 15 watt or less bulb is the only thing FMR (The Worlds Most Knowledgeable & Caring Supplier of Hermit Crabs)recommends(you may verify this via FMR at 1-800-535-2722 M-F 5-9 Eastern time….ask for Kathy), anything more will dry your crab and your tank out and could easily “bake” your crabs. Some strong bulbs have also been known to cause sunburn on hermit crabs. An incandescent nocturnal black light bulb coated with rare earth element to stimulate the natural glow of the moon is preferred. They can see a little better at night and you can see them a little better. They tend to like the extra atmosphere might be a little more active; they will even often bask in the glow at night. Turning the moonglow bulb on and off CAN create temperature changes that might cause stress to your crabs so keep it on all the time. Moonglow bulbs are not recommended as a primary source of heating and are best used in conjuction with

An Under the Tank Heater- FMR makes one for tanks under 5 gallons that meets all specifications for Hermit Crabs and this 4 X 6 inch heater can be used on both a plastic ‘critter keeper’ and glass aquariums. You can order it online at petdiscounters.com if your pet store doesn’t have it. Other companies manufacture them in larger sizes and temp ranges. Make sure it will not heat your tank over 80 degrees F. You want to allow for some warmer and cooler areas on the tank, so it is not a good idea to buy a heater to cover the entire bottom of the tank. Unless you go into a really high quality product, you probably will not find a heater that can be regulated via a thermostat and many will raise the tank 10 degrees above whatever the original temperature was. Adjusting substrate depth is the best way to regulate the temps. Be sure to keep your water pool and natural sponges directly above the heater because this will help ensure proper humidity levels.

Keeping a large sponge in a dish with water in it, over the heater is good for raising humidity. The water (warmed by the heater) is drawn into the sponge which helps ‘disperse’ the humidity into the air a little better, by providing a larger surface from which the water evaporates. You can order under the tank heaters that heat tanks up to 60 gallons as well as FMR’s brand online at petdiscounters.com if your local pet store doesn’t have one.

What Not to Use for Heating

Don’t use a heating rock as these are generally made for lizards and get too hot. The crabs may also climb on top of them causing great harm and the heat is too centralized. Also do not use a heating pad as they are not designed for this particular use. They need air ventilation and circulation that properly designed undertank heaters have and regular heating pads don’t. Heating pads will melt plastic and bake crabs.


Keep a thermometer in the cage and be sure to turn off any heating equipment when the substrate gets too hot. If it is the summer time and your house is very hot you can keep the tank on the floor(hot air rises), invest in an air conditioner, keep them in the shade and out of direct light, keep windows open, provide drinking water that is a bit cooler than usual, etc.

Crab-Gloo history, by CLD

“Folks: I am going to add a little to an earlier post. I wanted to back up what Jenn posted about using the foam board as an insulator. It has been a staple at Kritterland from the beginning!

My first crabs were adopted in the middle of the winter in February of ’97. They were in a medium sized plastic ‘kritter carrier’… I was very concerned about taking them out in the cool air, knowing that they shouldn’t get chilled…. We were at an indoors Arts and Crafts show….and as we were looking I saw the ideal remedy….Someone was selling those soft-sided insulated lunch/beverage coolers. SO……….. my new guys came home warm and happy that night.

The ‘six-pack’ size worked for that medium carrier! We now have several sizes of carriers and coolers just ‘incase’… the first one stays in the car just incase we go to a pet store…. Works great in the summer too to keep the sun from baking them…another serves as a back-up ‘iso area’

Now, the problem of warmth after getting them here…was another concern! Being a former art teacher, I had some foam board sitting around so I got out the old exacto knife and we created an insulated ‘box’ to go around the carrier… This was adapted to work with each upgrade to larger tanks…with the foamboard around the back and sides of the tank… (one sheet of foamboard takes care of a ten gallon tank.) It was cheap and worked well. Since then I have suggested it to many folks as an alternative. I used this while doing my studies with the undertank heaters and nocturnal light bulbs. I found that I could MAINTAIN a much better and consistant temperature level with the three-sided insulation than without it. I have passed along this suggestion to many others and it works quite well in a school setting….allowing the kids to change the backgrounds with their art work…. I do have ‘front covers of foam board to use in case of an emergency ….

have used other colors but prefer the white foamboard… and using clear or white tape to make the hinged ‘corners’… have used velcro to secure the pieces also… So since then we still use the insulation idea… plus, the crabs can see their reflections better and their activies at that are very entertaining!

I like the fact Jenn gave this ‘thing’ a name…. “Crab-gloo” is much more catchy than ‘the box’… Have fun with this and let your imagination go wild. One school here had a contest to see which class had the best ‘backdrops’ for their crabs… some changed the background weekly….it was great fun and a good project for both art and science lessons…. with the little hermies benefitting from all the fun ‘environments’created just for them. As Jenn pointed out this is a fairly cheap way to go until you can get alternative heating! Have fun and Happy Crabbing! CLD” Message 353 at Hermies Yahoo!Groups

MoonGlow Bulbs and more by Jenn:

It is best to do as Crablover Don did and leave a moonglow bulb and heater on twenty-four hours and regulate your tank tank temp and humidity by using a piece of cardboard, spool of thread, or something to prop open your glass top (you can place plastic wrap or towels over 2/3 of a screen top), and by increasing the depth of the substrate OVER the undertank heater and keeping your water pool and natural sponges above the heater. He was also able to stabilize the temperature by placing foam on the outside of the tank on 3 sides.

From: “Jenn Borgesen”

Hi All! I’m back, but am still in the process of transferring data from my old computer to the new! I am tickled to see all the great topics being discussed on the list and ‘naturally’ I just have to toss in my two bits here and there! Cold Crabs: Seems to me we had this discussion last spring and again last fall! To recap … Yes, E crabs are particularly susceptable to temperature fluctuations. I know it is hard to keep things stable when one day you’re running the furnace and the next day it’s the a/c! Here’s some of the stuff that’s been offered up in past discussions to help maintain even temperatures in your crab tank … 1. Build a Crab-gloo! I think I have the basic instrux somewhere on my old system, but if a list member still has it handy … please feel free to post it! Basically, using your tank measurements, foam board and duct tape, you can build a quickie shelter to help hold in the heat when the temp starts to dip. Use your tank measurements plus 1″ to construct a 5 sided shelter. Don had a couple of those zip up 12 pack ‘coolers’ … he’d place one of his smaller plastic molting tanks in it to keep babies warm on the way home from the store … again any kind of insulation will help keep warmth inside the tank. 2. Hot water bottle …. just like it sounds, if the power is out and the temp is dropping fill a plastic bottle with hot water and place it in the tank to help create radiant heat to keep your babies warm. This can be done in conjunction with the above Crab-gloo 3. Make sure the tank is well away from direct sunlight and drafty areas … a well sheltered spot along an inside wall is best. Hope this helps! New Tank … Rick, it sounds like you are coming up with some great ideas and I am glad to hear that any heat from a blowdryer will not come into contact with the crabs. On the subject of under the tank heaters not covering the full bottom of the tank … you really don’t need them to. Having only half of the tank covered can become quite a benefit, especially if the temp should fluctuate as in the above – cold crabs – The crabs will have opportunity to self regulate if only half of the tank bottom is heated. If things get too hot they can move to the cooler side and conversely if the temp falls! Some crabbers who live in colder climates do use two heaters in winter to get complete bottom coverage. But I find with a closed lid system one UT heater designed for your tank size (ie 5 gal, 10 gal, etc.) is sufficient. Gotta run fer now guys … time to zip a few more files! :)Jenn

Messages from Hermies Yahoo!Groups:

What do I do to keep them warm?!

You can surround the tank with insulation — styrofoam or blankets work best. Fill the water and food dishes first, so you don’t have to open the tank and let heat out later. If you have a cooler chest and still have power, make up some hot packs now — hot water bottles, or soaked hot washcloths in a ziplock bag — and hopefully the chest will keep them warm for use later if needed.

We lost power and were snowed in for two days last year, and I actually resorted to putting all the guys in a critter keeper (easier to do then, I had 7, not 28!) and took them into the car with the heat turned on full blast — just made sure to keep lots of water in the tank so they didn’t get too dry. I think I also used the car heater to warm up some water for a hot pack for the tank, too…

HTH, and hope your weather has settled down a bit,



Fom: “jenn_borgesen”
Bracing for Bad Weather

Hi all ..

Woke up to about 6″ of that white fluffy stuff this morning. The good news is that it was so warm yesterday (61 deg!) that a lot of it is melting on the pavement. But what was left was oh so heavy to shovel, no exercise needed for me today!

The bad news … the snow is really sticky and is all over the trees and powerlines. Very pretty, but bad news if we get much more of it or if the wind picks up! My poor Canadian Hemlock tree looks like a closed umbrella, tons of snow holding down the branches! So we’re prepping for a potential power failure here just in case!

I do have a gas hot water heater so I can make up hot water bottles to help keep the crab tanks warm … and I’ve already taped together a crabgloo and pulled out old blankets to wrap the tank should the worst occur!

Hope everyone else in the storm’s path is doing well!


We’ve got about 6″ of snow with frozen rain on top, but thankfully the power is still on. I see there have been some great help posted for folks without power … in times of real desperation, we’ve used hot water bottles, towels & blankets and once I even put crabs into a paper lunch bag, stapled the lid and slipped them into the inside pocket of my down jacket to transport them to warmer quarters with the rest of the family.

From: “hermies_owner”
Subject: Re: Another Humidity Dilema

Hi Sharon,

I had a feeling this may happen. As I said on the phone, once you get the humidity up to a good level, it often stays in the tank and sometimes rises a little high. I would stop dampening the driftwood and perhaps place it in a plakkie bag (as Craig calls it) and sanitise it in the microwave or dry it out in the sun.

The humidity level will change as the weather warms up (as it has done over the last week here in Tassie) and this is one of the reasons the humidity gauge is so essential, so that we can maintain the humidity when need be. What is the humidity level now? 85 isn’t too bad, but if it goes above 90 you may find condensation on the sides of the wall and perhaps the beginning of bacteria problems if left unattended. I know that isn’t the case with you, but just that it can happen.

There have been times when my humidity level snuck from 75 to 90 overnight, so I did the standard things of placing the water dish over the unheated side, turned the UTH down only slightly, and left the lids off for five minutes or so while I washed out the bowls and refilled the food dishes. Sometimes this is all that I need to get the humidity level to where it need be.

Basically it is trial and error until you find what works best for your enclosure. As always, you know I’m only a phone call away 🙂

Look out, though… antarctic blasts are headed our way! Under Tank Heater alerts, and perhaps create a CrabGloo from Don’s example of four walls of styrofoam cut to measure, then taped up to help insulate the tanks. Being the Art Teacher that he was, Don also recommended decorating the CrabGlo while you are trying to keep warm, creating not just an insulation but a background while you are at it!

Past background painting competition entrants can be found at http://comps.aboutlandhermitcrabs.com

Take care!


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