Molting is important to tarantulas for a variety of reasons.
Possibly the biggest reason why tarantulas molt is to allow them to grow larger.
However molting also offers an opportunity to regrow missing body parts, including urticating hairs that have been kicked off in the past.
Lastly, molting is necessary for male tarantulas to reach maturity so they are capable of reproduction.
Molting for Growth
A tarantula’s tough exoskeleton helps to protect the soft insides as well as minimising water loss in drier habitats. The downside to having a firm outer skeleton is that they don’t stretch as you grow. In order to grow larger a tarantula – like other arthropods – must molt.
The tarantula splits open the old skin and clambers out of it. Once out of the old skin, the tarantula carefully inflates it’s soft, new, pliable skin. For example, many tarantulas that have recently molted will look like they’re performing yoga – they will stretch their legs into unusual angles and positions. This is to help “stretch” the skin and ensure it hardens correctly.
Over a period of hours and days this new skin hardens. Eventually it becomes as tough as the old skin, though this process can take a few weeks. The end result, however, is a much larger tarantula. Typically a freshly molted tarantula will not only be bigger than it’s previous version, but the colors will be brighter and more vibrant.
Molting for Regeneration
Tarantulas are able to regrow lost limbs, mouthparts and urticating hairs when they molt.
Legs may be lost, for example, as a result of a tarantula being attacked by a predator. A tarantula that is grabbed by it’s leg may opt to “drop” the leg, so that the spider itself can escape.
Obviously losing a leg presents problems for the tarantula, and it is a trick that can only be used so many times. Tarantulas do only have so many legs after all.
Fortunately, tarantulas are capable of regrowing their legs when they molt. The new leg begins to grow inside the tough outer exoskeleton. When the spider molts, the new replacement leg is revealed.
Depending on the size of the tarantula this may be a full-sized replacement for the lost leg, or it may be smaller and more spindly. Even so, this regenerated leg will continue to grow with subsequent molts until it reaches the size of the original lost leg.
Molting for Reproduction
Tarantula mating is curious.
Adult male tarantulas display some interesting and unusual adaptations. For example, many adult male tarantulas have hooks on their front legs. These hooks are used to gently hook the female’s fangs out of the way. Once hooked, the male tarantula is at far less risk of being eaten by the female. It can also make the mating process much easier for the male.
That said, it is only mature adult males who possess these unusual appendages. And it is only through molting that these adaptations come about. Younger male tarantulas will look just like equally-sized females.
When the male tarantula reaches what is known as their “ultimate” molt, however, they will emerge with these modifications, ready for reproduction.
How Often Do Tarantulas Molt?
A variety of factors can affect how often tarantulas molt. Many adult tarantulas will only molt once a year, though it is not unusual for large adult females to go for much longer without molting.
The story is rather different for smaller/younger tarantulas. Tiny baby tarantulas are capable of molting every few months, though the period of time between molts typically increases as the tarantula grows and develops. For larger tarantulas the period between molts is typically 3-6 months.
Upon reaching adulthood, however, this typically slows down to the “once a year” pattern.