The first thing we do when getting a hermit crab is to give it a name, so you need to know how to tell if a hermit crab is male or female.
Unfortunately, sexing hermit crabs isn’t always easy because gender differences can be subtle.
The easiest way to sex hermit crabs is to check their legs. Male hermit crabs have hairy legs, while female hermit crabs have smooth legs.
Females have two tiny sexual organs, called the gonopores, atop their third set of legs. Also, young males gain size and mass faster than females.
Pairing them in opposite-sex groups is safe as captive hermit crabs rarely mate.
Is My Hermit Crab a Boy or Girl?
How do you know if a hermit crab is male or female? You’ll need to get a look at your hermit crab out of its shell, but never wrench a hermit crab from its home for gender identification.
Some physical characteristics are almost identical between male and female hermit crabs.
For example, it’s impossible to differentiate between a boy and girl hermit crabs by claw size. Some say that females have larger claws, but this claim has no scientific basis.
Instead, you’ll need to review physical characteristics and, to a lesser extent, behavior. Once you know what you are looking for, sexing hermit crabs will become second nature.
The differences can be subtle, so you may need to take more than a cursory glance.
Physical Appearance
In many species, the size of an animal can be used to detect sex.
Usually, the male is larger unless the female has to carry sizeable embryos, but this isn’t the case with adult hermit crabs. Once grown, hermit crabs stay about the same size.
There are some discrepancies, especially when young, because hermit crabs grow and molt at different rates based on sex. Male hermit crabs grow quickly, regularly molting. So, a young male may tower over a female of equivalent age.
Females grow slower as hermit crabs breed while young, usually in the first year of life. This is a matter of survival because females carry their young in an egg sac attached to their legs, which makes them vulnerable. By growing more slowly, a female is likelier to find suitable shells to hide within.
During mating season, male hermit crabs can grow in size. Many males molt ahead of mating and emerge larger. This doesn’t make them any more appealing to females; it just gives them a better chance of overpowering rivals for a potential mate.
Where physical appearance differs is the legs, as male and female hermit crabs have 10 legs. In females, these will be completely smooth; in males, the legs are covered in coarse hairs.
Additionally, females have 3 appendages on the left of the abdomen, and males lack these. These appendages (pleopods) double as a sac for a female to carry her unborn young.
Sexual Organs
Male hermit crabs have a penis below the fifth set of legs.
The Royal Society of Open Science stated that this organ could be disproportionately large relative to body mass. It can be 60% of its body length, which is an evolutionary tactic to protect the shell.
As discussed, males grow faster than females, which makes appropriately-sized shells a rare commodity. To avoid losing their shells, male hermit crabs develop a large penis. This enables males to mate without vacating the shell, avoiding leaving it available for a rival.
The sexual organs of the female are called the gonopores; these are two tiny openings above the third pair of legs. You may need a magnifying glass to identify gonopores.
Behavior
There are some obvious differences in temperament between male and female hermit crabs. Don’t rely on watching behavior to determine the sex of hermit crabs. There are some variations, though.
Females are sometimes more confident and outgoing, so they explore new terrain. They may find a range of hiding places, while males are likelier to find one location as they feel safer.
While this can be linked to basic survival instinct, it may pertain to mating. According to Biological Sciences, hermit crabs with high fecundity breed less due to higher rates of mortality associated with risk-taking behaviors.
More cautious males tend to enjoy greater success with breeding. Remaining careful helps hermit crabs live longer and enjoy more mating cycles.
These mating rituals can lead to other conduct between sexes. Sexually mature males guard females that they want to breed with. As explained by Behavioral Ecology, guarding behavior can lead to conflict.
If you see several hermit crabs surrounding each other, the object of attention is likely a female. The interested parties will be males hoping to gain her favor.
As captive hermit crabs rarely breed, this approach is unlikely to get results.
Male vs. Female Hermit Crabs
There are differences in appearance and conduct between male and female hermit crabs. This table summarizes the variations between the sexes. Here’s how to ‘sex’ a hermit crab:
| Male Hermit Crab Identification: | Female Hermit Crabs Identification: |
| Hairy legs | Smooth legs |
| No legs on the abdomen | Legs on the left of the abdomen |
| No abdominal appendages | Three feathery appendages left of legs to carry eggs |
| Has a penis below the fifth set of legs | Has gonopores atop the third set of legs |
| Increase size and mass in mating season | Size remains consistent in mating season |
| Grow in size quickly from a young age | Slowly and steadily increase in size with age |
| Keen to reproduce during mating season | Rarely receptive to mating in captivity |
| No sexual pheromones | Releases pheromones if receptive to mating |
| Attracted to larger females | Indifferent to the size of males |
| Stick to familiar terrain | Seek a variety of different habitats |
| Remain shy and cautious | Can be bolder and braver |
With over 800 different species of hermit crabs, variations will occur. However, following the above guidelines will enable you to ‘sex’ a hermit crab.
Do Hermit Crabs Change Sex?
Some owners claim that their hermit crabs change sex during their lifetime, but this is unproven by science. It’s more likely that changes in physical appearance led to mistaken identity.
Despite this, hermaphroditism is common in invertebrate species. For example, if a clownfish is born a male, it can change sex irreversibly to become a school’s dominant female. Oysters and shellfish, closer relatives to the hermit crab, do the same thing.
All the same, hermit crabs aren’t believed to change sex. However, the Journal of the Marine Biological Association of the UK confirms they can be intersex. These hermit crabs live as males after molting; the gonopores close, and the hermit crab mates as a male.
Can Male and Female Hermit Crabs Live Together?
The Journal of Ethology stated that hermit crabs could detect gender within their species.
This becomes increasingly apparent in the wild during the mating season because males will ignore each other while actively seeking out females.
Hermit crabs can’t be spayed or neutered, which is usually a problem. In reality, captive hermit crabs rarely mate because it takes a certain environment and a skilled person to get this to happen.
Females must be willing to mate with an eligible male. As per the Journal of Crustacean Biology, males can’t force mating with disinterested females. Larger hermit crabs have no biological advantage in reproduction, but larger ones usually emerge as the victor.
There’s no harm in pairing mixed sexes. Despite their name, hermit crabs are a social species, so they like to live in colonies of up to 100. Denying this opportunity on the grounds of gender leads to loneliness.
The easiest way to sex a hermit crab is to wait for it to emerge from its shell. When it does, assess its legs. If the legs are hairy, you have a boy; if the legs are smooth, it’s a girl.
