All hermit crabs have four antennae, divided into two pairs. The antennae act as a hermit crab’s sense of smell, work in lieu of ears by detecting vibrations in the air, help guide food into the mouth, and work as feelers while hermit crabs travel around.
The antennae of a hermit crab are constantly active, even twitching while a hermit crab is sleeping. This is because the antennae warn them of any potential dangers.
You’ll likely notice hermit crabs fencing and wrestling with their antennae. Feeler fights are recreational or sometimes used to assert a social hierarchy and settle disputes in a colony.
Hermit crab antennae are quite fragile and can be broken off. Part of the exoskeleton, antennae, will regrow and be replaced during molting. Until this happens, a hermit crab’s senses will be slightly dulled.
Do Hermit Crabs Have Antennae?
All hermit crabs are born with antennae, regardless of size, species, sex, or whether they’re native to land or sea. While the color of antennae can vary, they’ll always be found on the head.
Hermit crabs maintain and utilize their antennae unless they break off by accident or design. Sometimes the brittle antennae break or snap through wear and tear, but chelipeds can sever them.
How Many Antennae Do Hermit Crabs Have?
Hermit crabs have four antennae. Two are long and straight, colloquially known as feelers or primary antennae. A further pair of secondary antennae accompany these feelers, or antennules slightly bent around the head.
What Do Hermit Crabs Have Antennae For?
We understand the basic biology of hermit crab antennae but not their purpose. Two questions remain – what do hermit crabs use their antennae for, and how does the antenna help a hermit crab survive?
Hermit crab antennae are responsible for their five core senses. Hermit crabs don’t have ears, so the antennae compensate by detecting sound. The antennae also provide a sense of smell and touch.
Sense of Smell
The secondary antennae of a hermit crab act as a sense of smell.
According to the Journal of The Royal Society, their antennules react to water vapor in the air, picking up food scents or potential hazards.
To ensure hermit crabs enjoy a superior sense of smell and maintain a healthy appetite, always keep a supply of saline water in the habitat, which should take the form of a bathtub in the tank.
Assisting with Feeding
As well as the power of scent, the antennules are intrinsically linked to taste in hermit crabs.
Hermit crabs decide if they want to eat something based on its smell. Strong, sweet aromas are the likeliest to pique the interest of hermit crabs.
Hermit crabs lack teeth, which makes eating more challenging. Once a scent has captured a hermit crab’s imagination, the snack will be cut into tiny, bite-sized pieces by the large cheliped.
From here, the hermit crabs must guide the food into their mouths. The smaller cheliped will be used for this, but it can be clumsy. The antennules will help guide any morsel into a hermit crab’s mouth for chewing and swallowing.
Sense of Hearing
Hermit crabs don’t have ears, so they ‘hear’ by picking up on vibrations. This is primarily achieved through tiny hairs on the legs, which detect ground-level vibrations.
According to The Evolutionary Biology of Hearing, the antennae will also react to changes in the atmosphere caused by vibrations. A hermit crab may twitch its antennae to gain an understanding of the sound or plunge them into the substrate for a superior reading.
Negotiating Terrain
Hermit crabs have two eyes mounted on stalks that can rotate to all angles.
Despite this, it’s commonly believed that hermit crabs don’t rely on vision to explore the world around them. Instead, they use their primary antennae to feel their way around.
Hermit crabs won’t necessarily struggle to make their way around without eyes, but broken antennae make them considerably clumsier.
Recognizing Conspecifics
We’ve discussed how hermit crabs use their antennae to negotiate the world around them, but what does it mean when hermit crabs touch antennas?
In most cases, this is an exchange of information and a search for recognition.
The Journal of Chemical Ecology confirms that hermit crabs can recognize each other by touching feelers. Hermit crabs use this to memorize which tankmates are friendly and docile and which are best avoided.
Interacting with Tankmates
Once a hermit crab has used its antennae to determine whether a conspecific is a friend or foe, it may continue interacting using the feelers. Often, this takes the form of fencing or wrestling with antennae.
Sometimes, this is harmless fun – hermit crabs pass the time through play. In others, feeler fights are an attempt to settle a dispute diplomatically.
Playfighting
To pass the time, hermit crabs sometimes indulge in feeler fights and antennae wrestling. As long as both parties enjoy the interaction, there’s no reason for concern.
Settling Conflicts
Hermit crabs also use feeler fights and antennae wrestling to settle disputes within a colony. Arguments that may arise among your pets include:
- Battles for territory within the tank.
- Establishing a rank of colony alpha.
- Fighting over the right to live within a preferred shell.
Most hermit crabs are docile and prefer to settle these disagreements as amicably as possible. This means they’ll engage in a comparatively gentle bout of antennae wrestling, and hopefully, both combatants will accept the result in good grace.
Feeler fights can turn nasty. Listen out for loud, intense chirping, which suggests one or both hermit crabs are afraid. If one opponent grows too aggressive, they may start pinching with claws, potentially severing legs, antennae, or eye stalks.
Do Hermit Crabs Urinate from Their Antennae?
Hermit crabs urinate from glands just between the eyes and the antennae.
This means some people mistakenly believe that hermit crabs pee through the antennae. Hermit crabs urinate multiple times a day, but in tiny amounts that are usually invisible to the naked eye.
My Hermit Crab is Not Moving its Antennae
It’s rare for a hermit crab’s antennae to remain completely static for a prolonged period.
Hermit crab antennae constantly twitch while sleeping, so they can avoid environmental hazards.
Something may be amiss if your hermit crab is above found and hiding in its shell without moving the antennae. The two likeliest explanations are:
- It’s overstimulated and distressed by excessive noise and is attempting to calm down.
- There is not enough saline water in the enclosure to stimulate its senses.
Try to resolve these concerns by replacing the saltwater in a tank and relocating the habitat somewhere quieter. If this does not help, isolate the hermit crab in case it’s unwell.
My Hermit Crab Severed Its Antenna
As discussed, antennae can be lost in a hermit crab fight. Sometimes, hermit crabs also sever their antennae using their chelipeds.
If a hermit crab cuts off its antennae, it may be stressed and overstimulated. As mentioned above, a hermit crab will initially cease using the antennae to enjoy a moment of calm. If this doesn’t help, it may resort to self-mutilation in the act of desperation.
Hermit crabs may also sever their antennae if they have been damaged somehow. If the antennae are no longer functional, the hermit crab will lop them off to encourage the growth of a replacement. This action is most common when a molt is impending.
What Happens if a Hermit Crab Loses an Antenna?
Having established that the antennae are critical to a hermit crab’s daily experience, it’ll be concerning if a hermit crab loses an antenna. Unfortunately, as hermit crab antennae are brittle, this is always possible.
If an antenna is snapped off in a feeler fight, willingly severed by a hermit crab themselves or a conspecific, or broken in an injury (such as falling from a height,) a hermit crab may initially become a little clumsier and bump into obstacles or tankmates.
You may also find that you need to manually stimulate your hermit crab’s appetite, as its sense of smell will be diminished. According to Modern Psychological Studies, adding a blue-hued light will encourage hermit crabs to eat.
The antennae are part of a hermit crab’s exoskeleton, so they’ll regrow during a molt if lost. The antennae may take two molts to regrow and regain full function, but a single molt will recommence the process.
