Hermit crabs are the most popular type of crab in pet stores. This is because they are considered to be low-maintenance pets, even though this isn’t necessarily true.
Their unique characteristics, their curiosity, and their supposed cuteness also factor into them being very popular as pets.
Having over 800 species, they are native to the Indo-pacific region and come in different sizes, with different habitats.
Some of them are mostly aquatic, spending their lives in water and only coming up for short periods or never coming up at all. The rest are semi-terrestrial and terrestrial in nature. The land hermit crabs will live near the ocean so that they are able to replenish their water supply, find mates and look for food. They do not necessarily live by the ocean. They will find their habitats in marshy areas as well as forests near the ocean.
Hermit crabs have both a hard and soft exoskeleton, which needs to be periodically shed so that they can grow. The shedding of this exoskeleton is called molting, which we will focus on in this article.
Anatomy of a hermit crab
To understand molting, we first need to understand some of the structures of the hermit crab. Some of the parts of a hermit crab include the following:
As mentioned earlier, a hermit crab has a hard exoskeleton as well as a soft one. An exoskeleton is a hard outer covering used for protection. The hard exoskeleton covers the front half of the body, while the softer one covers its long abdomen.
Hermit crabs have ten legs, the first pair is the chelipeds, also referred to as claws. The chelipeds differ in size, with the smaller one used mainly for feeding purposes and the longer one for defense. If you disturb the hermit crab, it will use its longer cheliped to pinch you.
The second and third pair are walking legs, the fourth pair is used for moving in and out of the shell while the fifth pair is used for cleaning the gills and shell. The final two pairs of legs are also useful in supporting the shell.
Hermit crabs do not have their own shell, they use mostly mollusk shells and shells of other crustaceans and when the shells no longer fit them, they switch to new shells. They use their shells for protection from predators and harsh weather conditions, they also store water in them for the molting process.
They also have two pairs of antennae. The first pair is longer and is used for touching and sensory purposes. The second shorter pair is used for tasting and smelling.
Hermit crabs use gills for breathing. They are located in the brachial chamber between the fourth and fifth pair of legs. They breathe oxygen through water, so the gills must always be kept moist which is why they carry water in their shell.
Now that we know a little about their anatomy, we can get into the molting process.
First, let’s get into some of the signs that molting is about to take place.
Related Why Did My Hermit Crabs Die?
Signs of an impending Molt
1. General inactivity and lethargy
Hermit crabs are nocturnal, meaning that they are more active at night than during the day. Right, when they are about to start molting, their activity dwindles, and they start showing little interest in movement and socializing with other crabs.
If your hermit crab suddenly becomes dormant, do not start the burying arrangements, it might just be ready to molt.
2. Changes in appearance
During this time, a hermit crab’s appearance will slowly start to change. The exoskeleton will start to look ashy and dull, and its shiny beady eyes will also start to look cloudy and dull.
3. Changes in smell
The hermit crab will also develop a strange smell, but this is not to be confused with the extremely foul smell it develops when it is sick and dying.
The hermit crab will start to dig more frequently. This is because it needs to burrow in the sand for privacy and protection from harsh external conditions.
5. Increased appetite
Hermit crabs generally do not have a lot of appetites, but when they are about to molt they start to develop a bigger appetite. This is because they need to store enough water, fat, and nutrients to survive the molting period. The store of water and fat can be seen as a large black bubble on the left underside of their bodies.
6. Regenerating limbs
Hermit crabs will sometimes shed their limbs as a result of stress and other factors. When they are about to molt, the limbs will start to grow back in the form of a gel-like nub. This nub will develop into a limb over time.
Hermit Crab Molting Stages – Molting Process
There are four stages of the molting process in a hermit crab;
- Premolt (also known as Proecdysis)
- Molt (also known as Ecdysis)
- Post-molt (also known as Metecdysis)
- Inter-molt (also known as Metecdysis)
In this stage, the old exoskeleton starts to separate from the surface of the skin as the new one is developing underneath it. The hermit crab starts storing enough fat, water, and nutrients necessary for its survival, and the calcium from the old exoskeleton is absorbed into the hermit crab’s tissue.
Consequently, the old exoskeleton is weakened so that it is easier for it to be shed. All the lost limbs will also start to regenerate during this stage and the existing ones will start to lose control as they shrink in preparation for shedding.
The molt stage is the shortest stage. The water and salts stored by the hermit crab are used by the hermit crab’s hemolymph to create enough pressure to break down the exoskeleton.
The whole body is shed, and the hermit crab will eat its old exoskeleton so that the chitin and calcium help in the hardening of the new exoskeleton.
The freshly molted crab which is now bluish in color starts to harden the new exoskeleton and regain mobility. The hardening of the exoskeleton takes place in two forms; sclerotization or tanning and calcification.
Sclerotization involves the combination of chitin and protein to make the new exoskeleton stronger and darker while calcification involves the process of the calcium reinforcing the exoskeleton.
This is the period between the start of the next molting phase. It is the longest period and involves further strengthening and bulking of the new exoskeleton.
Hermit crabs need to molt in proper conditions. They will produce a molting hormone to begin the process when conditions are right. Otherwise, they produce a molt-inhibiting hormone, which can rise to toxic levels killing them.
How long does it take a crab to molt?
A hermit crab’s duration of molting depends on its size. Small hermit crabs will molt for a period of 1 to 2 weeks, and they will do so multiple times a year. Average and medium-sized hermits will take 4 to 8 weeks to molt, and they do so one to two times a year. Larger crabs will take about 2 to 3 months and will only molt once a year.
Molting is a normal process in hermit crabs. When you notice that your hermit crab has retreated into the sand, do not attempt to dig it out. Just let nature take its course.