what lights do hermit crabs need?

Do You Need a Light for Hermit Crabs?

Hermit crabs are not accustomed to lamps and artificial light sources. In fact, too much light can be stressful. Like all animals, pet hermit crabs require an appropriate balance of light and darkness.

Hermit crabs need a natural cycle of 12 hours of light and 12 hours of dark conditions. This will replicate their living conditions in the wild. You should never leave a lamp on overnight in the enclosure. Instead, placing a habitat in a room with a window will enable hermit crabs to follow their natural circadian rhythms.

This does not necessarily mean that you can’t use lamps, but a natural approach to tank illumination is preferable. You need to replicate the wild habitat of hermit crabs as much as possible.

Do Hermit Crabs Prefer Light or Dark?

Hermit crabs are nocturnal by nature. In the wild, land hermit crabs spend their days buried under the sand to avoid the sun. They typically emerge at dusk and scavenge for food and shells. To say that hermit crabs prefer darkness would be an oversimplification, though.

Like all animals, hermit crabs are governed by a body clock. Hermit crabs must be able to differentiate between darkness and light. This helps them understand when to sleep and when to become active.

If you keep captive hermit crabs, you’re unlikely to see much of them during daylight hours. This is to be expected. Even by night, hermit crabs may not emerge in a brightly-lit room. This can be troublesome if you get hermit crabs as pets for young children.

You may be tempted to get a lamp so the youngsters can watch hermit crabs at play when night falls. Always place the needs of the animals first, though. Hermit crabs must have a natural balance of light and dark every day. Too much illumination is harmful, and even lethal.

do hermit crabs need a light at night?

Are Hermit Crabs Sensitive to Light?

The eyes of hermit crabs are undeniably sensitive to light. Excessive illumination will cause your pets no end of distress. Hermit crabs are used to moving, eating, and interacting in darkness.

This makes hermit crabs naturally averse to too much bright light. If you shine a light in the eyes of a hermit crab, it will retreat to its shell. Force them into light permanently, and they will grow confused and disoriented.

The initial impact of this will be bad enough. Your hermit crabs will grow reclusive, stressed, and unwilling to eat or drink. Eventually, they may take drastic action to escape light, including severing their eyestalks. If sufficient damage is done, these will not grow back during a molt.

Do My Hermit Crabs Need a Lamp in Their Aquarium?

So, you have a state-of-the-art habitat for your pet hermit crabs, and now a pet store clerk is pushing for a further sale. They are adamant that hermit crabs need lamps, but you have heard otherwise. Where does the truth lie?

The reality is, lamps and artificial light sources are optional for hermit crabs. Well, lamps can be dangerous for hermit crabs, if used incorrectly.

As discussed, hermit crabs grow stressed when exposed to excessive light. This stress will be magnified if the light source is artificial. As per Behavioral Processes, hermit crabs often respond to illumination with fear-based hiding. This stress can be avoided.

You also need to consider the logistics of lamps in an enclosure. Hermit crabs can be curious. They will likely see trailing cables as a rope toy to climb, or otherwise something to investigate. Pinching or biting a live cable may end badly for your pets.

Hermit crabs have excellent night vision. A lamp left on overnight will not be a source of comfort for your pets. Instead, it will confuse and upset them. Your hermit crabs prefer a dark night, as they automatically understand this is time to wake up.

Placing a hermit crab enclosure in a room with a window will typically provide plenty of natural light. This will aid your hermit crabs to maintain their circadian rhythms. Any artificial light is likelier to unbalance your hermit crabs more than aid them.

Do Hermit Crabs Need Light All the Time?

A constant source of light in an enclosure is harmful. Choose how your hermit crabs will receive their required hours of light each day. Natural light is best. If you choose an aquarium and location with sufficient access to natural sunlight, the needs of your pets will be met.

Factor this in when considering where to place a hermit crab habitat. Artificial light sources do not just stem from lamps. Streetlights outside a window, for example, can also cause distress to hermit crabs. Equally, a habitat too close to a window may overheat.

If you live in an area with prolonged hours of sunlight, or a constant source of external light that you cannot control, manage this. Close blackout blinds or curtains to the room’s window after dark. You could also toss a towel or blanket over the hermit crab enclosure. Just ensure this does not restrict airflow into the habitat.

Do Hermit Crabs Need a Light at Night?

Hermit crabs are entertaining but not always the most gracious animals. You may notice that your pets are clumsy, spilling food and water overnight. Do not make the mistake of thinking that this is because they cannot see.

Hermit crabs seemingly constantly bump into water bowls, and each other, at night. This is deliberate. Hermit crabs play by testing strength, colliding shells. They also deliberately spill water to add moisture to the substrate. It is not because they cannot see obstacles.

As per the Journal of Comparative Physiology, hermit crabs have refracting superposition eyes. This means that hermit crabs’ eyes contain cylinders and corneas that reflect light. These cylinders also store dim lighting.

If you’re lucky enough to get a good look at your hermit crabs, you’ll notice they have large, round eyes. This is not an accident. It helps the hermit crabs absorb and reflect any ambient light. This means that hermit crabs see perfectly well with limited light.

A night light – no matter how dim – is not worth the risk. Hermit crabs do not rely on vision to negotiate their surroundings. All hermit crabs have antennae, which are linked to touch and scent. These senses are considerably more important to hermit crabs than eyesight.

Light Options for Hermit Crabs

As we have discussed, a light inside your hermit crab enclosure is voluntary. It is rare that hermit crabs need artificial illumination. If you do decide to add a lamp in a habitat, you must ensure you select a safe option.

Ultraviolet Lights

Of all artificial light sources available to hermit crabs, ultraviolet light is considered the safest. In the wild, hermit crabs will be exposed to a degree of UV light through the sun’s rays.

This is more prevalent in terrestrial hermit crabs than their marine counterparts. As per the Woods Hole Oceanographic Institution, UV light typically only penetrates the upper 200 meters of the ocean. Marine hermit crabs dwell on the seabed, far from such exposure.

Ultraviolet light comes in three forms:

  • UVA light is the longest wavelength of the sun’s rays. This is what causes wrinkles and premature aging in human skin
  • UVB light is the most theoretically the most harmful, causing the skin to burn and potential cancer. It also provides Vitamin D, though
  • UVC light rarely reaches the atmosphere, usually failing to penetrate the ozone layer

This has led to some debate among hermit crab owners as to the necessity of artificial sources of UV light. UVC is irrelevant, as hermit crabs have never experienced this in the wild.


As mentioned, wild hermit crabs will likely have experienced some level of UVA light. All the same, it is worth remembering that hermit crabs bury themselves under sand by day. This is to avoid the harshest rays of the sun – and, by extension, prolonged exposure to UVA.

A UVA light is unlikely to ever be considered essential. Even necessary may be pushing it. If your hermit crabs live in a habitat completely devoid of natural light, it may help replicate wild surroundings. Hermit crabs that experience UVA can be more active after dark.

Equally, too much UVA light is definitely harmful. UVA lamps tend to be bright. This will eventually cause ocular pain to your hermit crabs. If you must use UVA light, filter it as much as possible. Overall though, a short outdoor playtime is a safer exposure.


UVB lights are often advertised as critical for hermit crabs. Do not fall for this – it’s purely sales patter. Some animals, most notably reptiles, will struggle without a UVB lamp. Hermit crabs can manage just fine without one, though.

Having said that, there are some advantages to a UVB lamp in a hermit crab habitat. Such a light source will provide hermit crabs with Vitamin D and calcium. This will strengthen the exoskeleton and boost agility.

By the same token, too much UVB will dry out hermit crab skin and gills. Never get a high-intensity UVB lamp. This can quickly lead to suffocation. It’s much safer to ensure hermit crabs get these essential vitamins and minerals from food.

So, do hermit crabs need UVB light? Again, ‘need’ is an overstatement. There are arguably more benefits to a UVB lamp than any other form of artificial light. This remains an optional addition to a habitat though. Only consider it once all other needs are met.

If using a UVB bulb, also consider placing it outside a glass tank. As per Photodermatology, Photoimmunology & Photomedicine, a glass aquarium offers an appropriate protective barrier from UV rays. As a little UVB goes a long way, this can be invaluable.

Halogen Lamps

If you have an old lamp with a halogen lightbulb in the house, you may consider adding it to a hermit crab enclosure. This will provide light, while any lampshade is also a hiding place. Unfortunately, halogen lights and hermit crabs mix like oil and water.

Halogen lightbulbs are a safety risk for two primary reasons. These bulbs run extremely hot when in use and are very delicate. Both these factors place hermit crabs in significant danger.

The heat produced by a halogen lightbulb is not sufficient to warm a hermit crabs enclosure. It will be an additional heat source, though. This can tip the fine balance of an aquarium temperature from comfortable to too hot. It will also dry out the substrate.

What’s more, your hermit crabs will likely prod and poke a halogen lightbulb. If they are fortunate enough not to burn themselves, they may shatter the bulb. Broken glass is a safety hazard. It will tear and shred their delicate underbelly. 

LED Lights

We have established that halogen lightbulbs must be kept far away from hermit crabs. Are LED lights safe for hermit crabs?

They are certainly safer, for several reasons. Most importantly, LED lights are cooler to the touch and virtually shatterproof. This offers a measure of protection. They will not break the bulb or be subject to excess heat.

If you must include a lamp for illumination, LED lights are better than halogen. They remain largely unnecessary, though. Only use an LED lamp if your hermit crabs are located in a room devoid of natural light, and even then, a shielded UVA bulb is preferable.

Heat Lamps

Hermit crab enclosures must remain above a set temperature. Typically, this will be around 80 degrees Fahrenheit – a little lower if your pets appear uncomfortably hot. Heat lamps are not the best way to provide this, though.

Hermit crabs prefer a steady and consistent distribution of heat. Your pets can experience drying out of the gills if exposed to a direct heat source.

If you use heat lamps in a hermit crab enclosure, choose the lowest wattage possible. Never point the bulb directly onto the substrate. Hermit crabs can easily burn themselves if you do so. The heat can also damage substrate and decorations.

Heat lamps for hermit crabs are only necessary for extreme climates. Undertank heaters are a safer way to keep your crabs from getting cold. Better yet are heaters applied to the sides of an enclosure. This will prevent burrowing hermit crabs from overheating.

do hermit crabs prefer light or dark?

Making Lights Safe for Hermit Crabs

If your hermit crabs have a genuine light-dark cycle of 12 hours each, they may not need any form of artificial light. This only becomes necessary if the enclosure has no access to natural light.

If you do decide to apply artificial lights, be safe. The golden rules of protecting hermit crabs from excessive or dangerous light are:

  • Avoid trailing cables with live electrical cables in an enclosure. Curious hermit crabs may pinch or nibble these cables
  • Do not let the hermit crab access light bulbs directly
  • Avoid brightly-colored bulbs as these can provoke a startle response
  • Keep light wattage as low as possible.
  • Never expose hermit crabs to 24-hour illumination, especially at night
  • Avoid shining high-powered heat lamps directly onto popular areas of a hermit crab enclosure
  • If you must use a lamp, invest in a timer switch in case you forget to turn it off at a scheduled time

Hermit crabs have a complex relationship with light. The simplest way to judge the illumination needs of your pets is to imagine they are still living in the wild. In their natural habitat, hermit crabs rely on natural light patterns. Replicate this to keep captive hermit crabs happy and healthy.