If you find your pet tarantula lying on its back, it is important that you do not touch it, as it is extremely fragile at this time. It can be quite alarming to find your tarantula lying in this seemingly unnatural position, but chances are it is simply because it is beginning to molt. Most tarantulas will molt while lying on their backs (though some will molt on their sides). Molting usually takes anywhere from 15 minutes to a full day, so keep an eye on your tarantula (remember to not touch it). You should be able to verify if it was molting by the evidence it has left behind in the form of the molt.
Many people think that if their tarantula is on its back, it means that it is trying to die. This is not the case, and it is quite rare that a tarantula would ever be found dead upside down. It is more likely to be found dead with its legs curled under it than to be found lying on its back.
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Signs of Molting
There are other, more subtle signs that a tarantula is about to molt, although some of these can occur for other reasons besides molting:
- A decrease in appetite. A tarantula getting ready for a molt will usually stop eating, sometimes for as long as a few weeks before a molt.
- A decrease in activity. A tarantula getting ready to molt will often become very slow and sluggish.
- Development of a bald spot. Tarantulas also sometimes develop a bald spot on their abdomen that grows increasingly darker as the molt draws near (a bald spot can also occur in New World tarantulas that have been kicking off their urticating hairs). After molting, the bald spot will be gone.
- Increased use of webbing. Tarantulas may make a mat out of silk for molting.
- Dull coloration.
If you notice the signs that a molt is impending, make sure the humidity in the tank is ideal and the temperatures are right for your specific kind of tarantula. The proper environment is important for a successful molt. Make sure there is no uneaten prey in the tank, as even a cricket can seriously injure—or even kill—a molting tarantula.
A Stressful and Dangerous Time
As the old exoskeleton is shed, the tarantula's body will be soft and extremely vulnerable. Though the actual molting usually takes a few hours, the tarantula's body will also be soft and vulnerable for several days before the new exoskeleton completely hardens. For this reason alone you should never handle a molting tarantula, or handle it right after it molts.
As mentioned before, make sure there are no crickets in the tarantula's tank and do not feed a newly molted tarantula for at least a week (to prevent new crickets from biting your tarantula before the exoskeleton has time to harden). The newly molted tarantula is so sensitive that even an innocuous little cricket can cause serious harm to them.
Since spiders have an exoskeleton, they must shed the old exoskeleton and form a new one in order to grow. Therefore, young growing spiders will molt more frequently (up to once a month) than older spiders (who may only molt every year or two).
Cowles, Jillian. Amazing Arachnids. Princeton University Press, 2018
Fordham, Margaret, and Brian K. Roberts. Emergency and Critical Care, An Issue of Veterinary Clinics of North America: Exotic Animal Practice. Elsevier Health Sciences, 2016
Tarantulas: Terrible or Terrific! Cornell University
Tully, Thomas N., and Mark A. Mitchell. Current Therapy in Exotic Pet Practice. Elsevier, 2016