Surprisingly beautiful under a microscope, the head of hermit crabs features long eyes on stalks and antennae. These are important to the survival and quality of life of all species of hermit crabs.
Hermit crabs have four antennae attached to their heads.
Two of these are long and straight, which are also known as feelers. The two remaining antennae are smaller and curved, which are more commonly used for eating.
Hermit crabs also use their antennae to hear, detect vibrations, and process information.
Hermit crabs can live without antennae, but it makes life more difficult for them.
What Are Hermit Crab Antennae?
Antennae are sensory organs found on all arthropods. Different animals use their antennae for varying reasons. Antennae are invariably attached to the head of an invertebrate.
Do Hermit Crabs Have Antennae?
Much focus of the anatomy of hermit crabs is on the legs, due to the unique gait of these animals. The head of a hermit crab is equally fascinating – and, naturally, even more important.
The scientific term for the head of hermit crabs is the cephalothorax. This describes the fusion of head and thorax. These comprise part of the hermit crab’s exoskeleton.
Within the cephalothorax, you’ll find a small mouth, two eyes on stalks – and antennae. These antennae are critical to hermit crab survival for several reasons. You will see antennae twitching near constantly.
All hermit crabs have antennae, whether based on land or sea. There are no differences in antennae anatomy between male or female hermit crabs. The color of antennae can vary, depending on which breed and genus the hermit crabs belong to.
How Many Antennas Do Hermit Crabs Have?
Hermit crabs have two pairs of antennae, meaning they have four in total. If you look closely at a hermit crab, you will see two slightly bent antennae flanked by two long, straight alternatives.
The longer pair are colloquially referred to as, “hermit crab feelers”, or the primary antennae. These are used by hermit crabs to negotiate obstacles and find their way around territory. These antennae also pick up on any scents in the air.
The bent antennae (secondary antennae, or antennules) are commonly used in taste and to aid eating. When a hermit crab picks up food using its pincers, the antennules ensure it reaches the mouth.
What Do Hermit Crabs Use Their Antennae For?
As discussed, hermit crab antennae have many uses. If you do not see the antennae moving, take a closer look. Even during sleep, these appendages should at least twitch – if not outright sweep the perimeter of a shell.
The antennae are primarily used to aid the senses. Also, hermit crabs use their primary antennae to interact with each other. This takes the form of wrestling, or ‘feeler fights.’ This is a standard play behavior in hermit crabs and not a concern.
Hermit crabs also urinate from small holes beneath the antennae. This leads to some owners mistakenly believing that hermit crabs pee from their antennae. This is not strictly true, but it certainly looks that way.
As discussed previously, all hermit crabs have two eyes. At a glance, as the eyes are mounted on stalks, they could be confused for further antennae.
A hermit crab’s vision has not been studied in detail. There’s an interesting experiment that shows that hermit crabs can see color, at the very least. Hermit crabs are shown different hues and showed varying hiding responses to the stimulus.
It is commonly believed that eyesight is not a primary tool for hermit crabs, though. These animals, where marine or terrestrial, rely more on the additional quartet of senses. Antennae, along with small hairs on the legs of hermit crabs, play a key role in this.
The primary antennae of hermit crabs are known as feelers for a reason. Hermit crabs use these antennae to negotiate their terrain. The primary antennae pick up any obstacles and foreign objects that may be nearby.
The primary antennae are constantly active. As discussed, they even sweep outside a shell during sleep. This ensures that nothing sneaks up on hermit crabs while they slumber. If antennae detect a threat, hermit crabs immediately wake up and hide.
The primary antennae can be used to pick up scents in the air. As per the Journal of the Royal Society, when they twitch antennae they are sniffing. From here, they acknowledge the presence of food, friend, or foe.
The presence of saltwater is essential for this sense. As per the Journal of Crustacean Biology, saltwater carries scents for hermit crabs. Without saltwater, hermit crabs struggle to detect food. This is why wild hermit crabs scavenge close to the ocean shore.
These senses of scent and taste are linked in hermit crabs. Hermit crabs decide if something is edible by the way it smells. If the primary antennae pick up an interesting scent, the hermit crab approaches. It then uses the pincers to move the food toward the mouth.
Alas, these appendages can be clumsy. As the food approaches, the secondary antennae detect the scent and move it into the mouth. If attempting to hand-feed hermit crabs, gently tap their secondary antennae. This assures the hermit crab that it is safe to eat the offering.
The primary antennae also play a significant role in the hearing of hermit crabs. As per The Evolutionary Biology of Hearing, hermit crabs pick up on audio cues by acknowledging and processing vibrations.
The legs are the first part of hermit crab anatomy to acknowledge sound. The antennae will quickly follow. If the hermit crab feels vibrations, the primary antenna will start to wave. The hermit crab may also plunge the feelers into the substrate.
This is an attempt at gaining a better understanding of the sound. It could also be an attempt to block out any white noise that is otherwise distracting. Animal Behavior explains that hermit crabs grow distracted and disoriented by constant, rumbling background noise.
If you spot your hermit crabs wrestling with their antennae, do not break them up. While a feeler fight may look aggressive, it is often playing. This is how hermit crabs decide upon a social hierarchy and exchange information. Only separate the hermit crabs if pincers get involved.
Feeler fights are how hermit crabs define strength and dominance. It is important to hermit crabs to assign a pyramid of supremacy. Unless the dominant hermit crab is hostile, all are happy with the outcome. Most will respect their place in the colony without complaint.
As discussed, hermit crabs also use their primary antennae to pick up on scent. By entangling feelers, the hermit crabs are getting to know each other. Chemical scents are exchanged and the hermit crabs come to a mutual understanding.
This also enables hermit crabs to recognize each other by smell. Hermit crabs remember their tankmates. By wrapping feelers around each other, they acknowledge a familiar presence. This minimizes the risk of territorial aggression in the future.
My Hermit Crabs are Not Moving Their Antennae
Hermit crabs failing to move their antennae can be a cause for concern. This suggests they are completely inactive.
Check that your hermit crabs are not sleeping. If they are piled together, this is likely. Place a food with a strong scent close to the hermit crabs. You will likely notice the primary antennae start to twitch. Even in their slumber, they are detecting the smell of a treat.
If this does not garner a reaction, avoid handling them. Something may be wrong, and handling will magnify stress. Before you panic that your pets are dead though, consider other explanations for static antennae.
Lack of Saltwater
As discussed, hermit crabs rely on the presence of saltwater to stimulate senses. If the saltwater in the tank has run dry, hermit crabs are essentially living in sensory deprivation. Replace this as quickly as possible.
Even if there is saltwater in the aquarium, take a look at the vessel. It could have lost much of the saline properties. Hermit crabs drink saltwater and store it in their shells to keep the gills moist. What’s left may be virtual freshwater.
It’s also possible that the water has been diluted by the urine of hermit crabs. Some hermit crabs also leave feces in bathing water while cleaning shells. These foul scents may be overpowering the salt in the water.
Consider changing the brand of marine salt, too. While all brands sold by exotic pet stores are suitable, your hermit crabs may have a preference.
Preparing to Molt
When hermit crabs are preparing to molt, they automatically become more lethargic. This can include the use of antennae. It is common for hermit crabs to cease seeking stimulation immediately pre-molt. Other signs that a hermit crab is due to molt include:
- Eating more than usual, storing fat
- Drinking and bathing more than usual, storing water
- Digging near-constantly, especially in one location
- Willfully spilling water on the substrate to create moisture
- Skin fading from a bright color to a pale gray hue
If you notice these symptoms, move your hermit crab to a solo tank. It will appreciate the privacy and peace while it molts. Leave the hermit crab alone in this tank until it completes the molting process. Only return the crab to the shared tank once it has a new shell.
Life in captivity can be stressful for hermit crabs. They are not used to human contact. What’s more, hermit crabs in captivity find it more difficult to escape overstimulation from light and noise.
Your hermit crabs may be attempting to find an oasis of tranquility. By keeping their antennae static, they are not actively seeking out scents, sounds, or illumination.
Consider if you can make life calmer for your hermit crabs. If there is noise in the room, such as music or television, turn it down. Dim any lamps and consider relocating the aquarium away from direct light sources.
Scent is arguably the most pivotal consideration. Aerosol spray like deodorant and air fresheners do not just smell strongly to hermit crabs. They can also contain toxins. Keep these far away from an enclosure.
Can Hermit Crabs Live Without Antennae?
The antennae of hermit crabs are brittle and delicate. This means this part of the anatomy can be broken or severed. As they are part of the exoskeleton, hermit crabs also molt their antennae. This means that hermit crabs can live without antennae.
Lost or broken antennae will eventually regenerate. Do not allow hermit crabs to be cavalier about antennae, though. As you can imagine, hermit crabs that lack these appendages can be clumsy. The hermit crabs may also grow distressed and anxious.
If you spot two hermit crabs fighting aggressively, separate them at once. As discussed, a feeler fight is no concern. Attempts to clip antennae with pincers must be curbed, though. In the rare cases of hermit crabs fighting to wound, antennae are easy targets.
The antennae are among the most distinctive features of the hermit crab anatomy. Help your hermit crabs keep their antennae in good shape. Do not panic if antennae snap or fall off as they will grow back within two molts.