Hermit crabs are captivating little creatures that have a unique life cycle. If you’ve ever wondered how these leggy crustaceans grow, molt, reproduce, and more, you’ve come to the right place!
If you’re short on time, here’s a quick answer to your question: Hermit crabs hatch from eggs as tiny larvae that float in the ocean before settling to the seafloor and finding an empty snail shell to call home. They molt and grow over time, upgrading to larger shells.
When mature, they mate and females carry eggs until they hatch into larvae.
In this comprehensive guide, we will cover everything you ever wanted to know about the hermit crab life cycle including their development and growth from larvae to adults, molting and shell upgrading, mating and reproduction, average lifespan, and more.
Larval Development and Settlement
Hatching From Eggs
After the female hermit crab lays her eggs, the embryo develops protected inside the egg case for around 3-4 weeks before hatching. Once ready, the larvae emerge from the eggs as zoea, appearing more shrimp-like than crab-like in form.
Amazingly, around 5,000-10,000 tiny zoea may hatch from one hermit crab female’s clutch of eggs! The hatching process and timing varies a bit between hermit crab species.
Pelagic Larval Stage
In the plankton-floating pelagic larval stage, the hermit crab larvae drift and swim in the ocean currents, molting and growing through several zoea stages. This lasts 1-3 months depending on factors like water temperature.
They are extremely vulnerable during this phase, with mortality rates over 99% in some species! Despite the odds against them, the fascinating abilities of the surviving larvae enable their eventual settlement.
Settlement and Metamorphosis
In the final larval stage, the postlarva develops sensory abilities guiding it to locate and settle in suitable coastal habitat rich in prospective shells. After finding a vacant snail shell for shelter, the soft larva undergoes metamorphosis into the form of a juvenile crab before emerging to start life in a new home!
This miraculous transformation marks the end of the hermit crab’s transition from a planktonic drifter to a lifetime as a bottom-dweller.
Growth and Molting
Finding That First Gastropod Shell
Hermit crabs are quite vulnerable without the protection of a shell. As larvae, they float in the plankton until they eventually settle to the sea floor and undergo metamorphosis into the crab form. At this stage, they are extremely small and defenseless.
Their soft abdomen is an easy target for predators. To reduce their chances of being eaten, hermit crab larvae frantically search for empty gastropod shells to crawl into and call home. This can be quite a challenge since there is fierce competition for shells and good ones are scarce.
But a hermit crab that manages to find its first shell greatly increases its odds of surviving into adulthood.
The Molting Process
In order for a hermit crab to grow, it must periodically molt, shedding its hard exoskeleton. Molting leaves the crab extremely vulnerable because its body is soft and exposed. Prior to molting, a crab stops eating for several days while it forms a new exoskeleton under the old one.
When the new shell has hardened enough, the hermit crab finds shelter and extracts itself from the old shell. This can take several hours. Having successfully molted, the crab swells up with water to expand its new soft shell before it hardens.
The cast-off exoskeleton is an excellent source of calcium and minerals for the other crabs, who eagerly feed on it. Hermit crabs molt frequently as juveniles, but the time between molts increases as they mature.
Upgrading to Bigger Shells
As a hermit crab grows, it must find a larger shell to accommodate its bigger body. Hermit crabs are quite particular about their shells and will spend hours assessing the available options to find the best fit.
According to a 2018 study, they select shells based on criteria like internal volume, weight, size of the opening, and exterior durability. Hermit crabs will eagerly abandon their current shell to upgrade to a better one. Finding a suitable new home can be challenging.
When multiple crabs want the same new shell, fierce fights can erupt. The availability of quality shells directly impacts hermit crab growth rates and survival.
Reproduction and Mating
Courtship Display and Mating
Prior to mating, male hermit crabs perform an elaborate courtship ritual to attract female crabs. The male waves his enlarged claw and uses it to tickle the shell opening of the female to entice her out.
He also performs a “dance” by standing high on the tips of his walking legs and rapidly bobbing his body up and down. If interested, the soft-shelled female will emerge from her shell and the pair will mate.
Fertilization and Egg-Laying
Following courtship and mating, the female hermit crab extrudes up to 18,000 eggs which she deposits under her curled abdomen. There the eggs are fertilized by the male’s previously deposited sperm. She carries her brood attached to the hairs on her abdomen for several weeks as they grow and develop, resemble tiny translucent spheres.
When the eggs hatch, tiny crab larvae emerge ready to enter the next stage of their life cycle.
Lifespan and Mortality
Average Lifespan in the Wild
In their natural habitats, hermit crabs live on average between 2 to 5 years. Their lifespans are significantly impacted by availability of resources, predators, and environmental conditions. Hermit crabs living in more favorable conditions with abundant food sources and few predators may survive over a decade.
Typical Causes of Death
The fragile exoskeletons and soft abdomens of hermit crabs make them vulnerable to predators like birds, fish, and octopuses. Without the protection of a snail shell, they are easily attacked.
Another major threat is competition for scarce resources like food, water, and shells. Hermit crabs may fight over an ideal shell, resulting in injury or death. Lack of food and fresh water can also lead to dehydration and starvation.
In captivity, improper habitat conditions are often to blame. Unsuitable temperature, humidity, substrate, or diet quickly lead to health issues. Shell fights rarely occur in captivity but can still prove deadly.
Extending Captive Lifespans
With attentive care, captive hermit crabs can live over 10 years and have been known to reach 20 years old. Key aspects involve:
- Spacious enclosure with at least 10 gallons per crab
- Proper heating and humidity between 75-85°F and 75-80%
- Adequate substrate depth for molting and digging
- Varied nutritious diet rich in protein and calcium
- Access to both fresh and salt water
- Hiding spots and ample shells to prevent competition
- Regular habitat maintenance and health checks
By replicating their natural environment and minimizing stressors, captive lifespans of over 20 years have been achieved. With attentive and knowledgeable care, hermit crabs can thrive and live full, long lives in captivity. For more tips, visit The Hermit Crab Association or Hermit Crab Answers.
Conclusion
From egg to adult, the life of a hermit crab consists of many fascinating stages as they grow, find shells, mate, and reproduce. Their need to constantly upgrade their borrowed shells makes them particularly interesting to observe.
Hopefully this outline gives you a comprehensive overview of the key events in the life cycle of these charismatic crustaceans. Understanding their development, molting process, mating rituals, and more allows us to better care for them in captivity and conserve them in the wild.
