How Often Do Lobsters Molt? (Explained)

As you may know, lobsters have hard shells that protect their bodies, called exoskeletons. Lobsters’ bodies can’t grow together with the shell, so they need to shed the outgrown shell in a process called molting. But, have you wondered how often lobsters molt? In this blog post, we’ll talk all about that, so let’s begin with a quick answer:

Lobsters’ molting frequency differs depending on the stage of their life cycle, but as adults, they molt once a year or two. Egg stage lobsters can molt every few days/weeks (35 times), larvae every few days (five times), and juveniles every few days/weeks (44 times). In general, the frequency of molting declines with increasing age.

However, this certainly doesn’t tell the whole story. Below I’ll explain more about how often lobsters molt in different life cycle stages. Furthermore, I’ll explain when they usually molt and what factors influence shedding frequency. Next, I’ll explain why and how they molt and if we can recognize that lobsters will molt soon. Read on!

How often do lobsters molt?

The frequency of molting on lobsters differs a lot in different stages of their life cycle. That’s why I will explain how often lobsters molt, depending on their stage. We can divide lobsters’ life cycle into four stages: egg, larvae, juvenile, and adult.

Egg

In general, the smaller the lobster, the more frequently it molts. This rule is simple because lobsters grow faster when they’re younger. A similar thing happens to humans. Lobster molts most frequently in the fertilized egg stage, which occurs after the female fertilizes eggs with the stored sperm from the male.

This lobster embryo can molt even 35 times, and this happens during 9-12 months because that much time a female lobster carries her eggs.

Larvae

After baby lobsters hatch, they become swimming larvae. In this stage, they molt about four to five times, and they enter a new larvae stage with each molt. The first stage larva is about eight millimeters (1/6 of an inch) long.

The second stage is already twice as large, and, depending on the species, it starts developing claws on its first three legs. With the next successive molt, the baby lobster enters the third stage larva and is about one centimeter (half an inch) in length.

After about eleven to fifty days of being larva, baby lobster molts again. It becomes a postlarva, is a little bit better swimmer and starts looking for a shelter at the bottom of the ocean. Once it finds it, it begins living on the bottom (being benthic).

Juvenile

After postlarva finds the perfect shelter, it molts again and begins its juvenile life. At the beginning of a lobster’s juvenile journey, it can shed about once a month or sometimes even more often. This means lobsters molt about 44 times before they’re even one year old.

During the second year, baby lobster molts every month, but its molting starts being seasonal. It mostly molts during the summer months when the water temperature is warmer. Thus, molting usually occurs from May to November.

After that, juvenile lobster molts further and further apart, continuing to grow for about five to ten years before reaching adulthood. On average, lobsters molt about 20 times during this period. Typically, during the third and fourth years, juvenile lobster molts two or three times a year. Fifth- and sixth-year lobster molts once or twice. After that, as its growth rate slows down, it sheds once a year.

Adult

After five to ten years, when lobster reaches adulthood, the molt gets less frequent. Lobster keeps growing all its life but molts only once every two or three years. In general, the bigger the shell, the longer between molts. However, females molt every time before mating season, about once a year or two as well.

When do lobsters molt?

Most of the time, lobsters molt during warmer months of the year. The molting season starts from early July to early September, but it can vary depending on the species and the location. During that period, lobsters often come closer to shore, to shallower waters, and molt there.

The rapid increase of water temperature and daylight hours during summer positively influence the hardening of new lobsters’ shells. Winter molting also happens, but it’s rare as it takes longer for the new shell to harden in cold water. The duration of hardening depends on water temperature, water quality, nutrition, and the size of the lobster.

Interestingly, females’ molt season is not always determined by their growth but because of the reproduction period. Usually, their mating seasons occur in summer, so this is also when they shed their shells. They do that every time before mating with a male. Once the male gives the sperm to store, the female fertilizes it with her eggs and won’t molt until the eggs hatch.

What are the factors that influence molting frequency?

Many environmental factors affect the growth rate and what comes with it – molting frequency. One of them is temperature, where warmer waters increase the growth rate of lobsters. Other factors are nutritional state, so if the food availability is low, lobster may grow slower, which increases the time between molts.

Furthermore, the presence or absence of other lobsters may also influence the time between molts. Scientists found that the species of spiny lobster grow slower individually than in groups. However, H. americanus – a species of clawed lobster – grows slower in a group than individually.

Other factors of lobsters’ growth rate and molting frequency are oxygen concentration and season of the year. Furthermore, the loss of appendages and their regeneration can also slow down the growth rate.

Why do lobsters molt?

There are two reasons why lobsters molt: growth and reproduction. The first reason why lobsters molt is because their shell (exoskeleton) doesn’t expand together with their bodies. Therefore, in order to grow, they have to shed their shell and replace it with new ones every year or two.

Another reason why lobsters molt is because females need to shed their old shells to store new sperm. Before mating, they remove their old hard shell together with the old pouch where they had banked sperm from a previous mate. After that, the female won’t shed until hatching.

How do lobsters molt?

It’s important to know that before molting, a new, fully formed shell is produced underneath the existing one. This means lobsters don’t “grow” a new shell after molting, but they harden it.

Molting begins by bringing the water inside the outer shell, which swells it and eventually splits on the back – between the tail and the upper body. Once it’s broken, the lobster flexes its body repeatedly until it’s finally out of the old shell.

The whole process usually takes about 15 to 30 minutes. After the molt, the new shell is soft, which makes lobster more vulnerable and careful. The shell will begin to harden, and sometimes lobster helps the process by providing nutrients from the old shell by eating it!

They do that because their molted shell is an excellent source of calcium they lost. By providing calcium, they’ll help in the hardening process of the new shell.

What are the stages between molting?

For most of the lobsters’ life, they either prepare to molt or recover from the last. We can divide the time between molts into several stages. In the first stage, lobster is soft-shelled and very vulnerable.

The second stage begins when the lobster’s shell starts to harden. These first two stages are called “postmolt” and identify the regeneration time after a lobster’s molting. The third stage is called “intermolt” and is the tissue growth period.

After that, the lobster enters the last stage – “premolt” – during which it prepares itself for the next molt. Most of the time, lobster is in the third and fourth stages, as postmolt stages are the shortest.

Are there signs that lobsters will start molting?

There are a few signs that can indicate that lobster will start molting soon. One of them is lobsters’ increased activity and movements. Lobsters often build shelters and barricade the entrances before molting. This behavior prepares them for the period when they will be vulnerable and more accessible prey for their predators.

Other signs include softening around joints and at the carapaces margin. Their shell usually becomes darker, and their limb buds’ growth increases for regenerating missing parts.

Sources

• Michel Comeau, Fernand Savoie, Growth Increment and Molt Frequency of the American Lobster (Homarus Americanus) in the Southwestern Gulf of St. Lawrence, Journal of Crustacean Biology, Volume 21, Issue 4, 1 October 2001, Pages 923–936, https://doi.org/10.1163/20021975-99990184
• J. Cobb, Bruce Phillips “The Biology and Management of Lobsters.” Academic Press, 1980