How do Spiders Grow:
(Moulting And Regeneration)

Arachnids (Spiders, Scorpions, mites, etc.) and most insects do not have skeletons like ours. We have our skeletons inside our bodies, like all animals.

Arachnids and Insects have external skeletons, which is their skin or shell. Now because insects have external skeletons, to allow them to grow they must grow a new soft skeleton underneath their existing one

When a spider moults it splits open it's old skeleton and wriggles out of it, the new skeleton that was growing underneath is soft and pliable, for a short while. The spider, once it is free stretches the new skeleton to allow some room for new growth, the new skeleton then hardens.

If a tarantula loses a leg or other appendage before a moult, after the tarantula has moulted it may have partially or fully re-grown the missing limb, this is called regeneration. Many reptiles can also do this.

When a tarantula moults it lies on its back with it's legs in the air, at this time the tarantula is very vulnerable and can be attacked and killed by the insects that it usually feeds on.

Example of an Internal Skeleton

brachypelma_smithi_moulting.jpg (4228 bytes)
Tarantula Moulting
brachypelma_emilia_moults_1.jpg (2474 bytes)
Tarantula Moults
(Click on each picture to enlarge)

The tarantula takes between two and twelve hours on average to complete the sheding of it's old exoskeleton (it's skin). Once this has been accomplished, the tarantula will not eat for two or more days, as it's fangs are still soft: the fangs are also part of the exoskeleton and are shed with the rest of the skin.

The tarantula is usually very weak and dehydrated after moulting. Most tarantulas, once they reach maturity only moult once a year or once every two years, depending on species. Spiderlings (baby tarantulas), moult up to eight times in their first year of life, each moult becoming progressively further apart.

Other Pages on Tarantula Biology:

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