In one sentence, describe what the following article is about:

Although illness is relatively uncommon, crabs can get sick. This is usually related to problems with their habitat, or “crabitat,” but may be a result of other issues such as mites. Hermit crabs need access to water to keep their skin moist and healthy. Examining your crab for signs of dry skin can keep your crab from drying out and ensure it can breathe properly. Signs of dry skin in hermit crabs can include:  Lack of water in the tank or on a sponge Matte appearance to the skin Excessive burrowing to get at moist spots in the tank The environment in the tank is vital to a hermit crab’s health and promotes its movement, too. If your hermit crab isn’t moving around much, the water in its habitat or even toxic paint on its shell could be killing it. Lethargy can also be a sign of stress.  Recognize that most hermit crabs like to play and will move around their habitats a lot if they are not molting or sick. Make sure your hermit crab is moving regularly and not hanging out of its shell, which can be a signal that it is dying. Remember that lack of movement can also signal molting. Foul odor coming from the tank can signal illnesses related to problems with the habitat. Check on your crabs every day, which can quickly signal you to any bad smells that might be coming from the animals or parts of the tank. Be aware that there may be a broad range of odors that can signal problems. These include: stinky feet, fish or shrimp, mildew or must, rotting food. Mites are arguably the most common cause of health issues for hermit crabs and you should be especially vigilant in checking for these. Be aware that there are “good” and harmless mites that inhabit crab’s spaces and bodies but that there are also “bad” and harmful mites. Watch out for the following types of harmful mites:  Gill mites, which are light pink or red and bury into the gills of hermit crabs. These mites are often not visible until after a hermit crab’s death because a flap of skin protects the gills of live animals. Crab mites, which glue themselves to soft parts of hermit crabs’ bodies including the eyes, mouth, or joints. Crab mites range in color from white to cream, grey, pink, or red. In addition to the physical symptoms of illness, hermit crabs may also exhibit unusual behaviors. Checking on your crabs daily will help you see each animals typical behavior—hermit crabs do have distinct personalities-- and can alert you to potential problems. Some behavioral problems to watch out for are:  Digging down into the habitat sand or coconut fiber to “de-stress” Consuming large amounts of food or water Soaking in the water dish Being very lethargic.  Hiding in its shell for long periods, especially if it usually enjoys attention.  Molting in the open.  Hanging out of its shell in a limp or lifeless manner. Sickness is rare among hermit and other types of crabs. However, there can be some confusion when trying to tell if your hermit crab is sick because many of the symptoms of illness parallel the signs of molting such as missing limbs and burrowing for days or months. Some additional signs that your hermit crab may be molting and not sick, especially if the crab exhibits several of these symptoms, are:  Digging Drinking large amounts of water or soaking in the dish Spilling water from the dish to dampen the sand or coconut fiber in the tank Cloudy eyes Ashy-looking skin, which is also called the exoskeleton Lethargy.

Summary:
Look for physical signs of illness. Examine for dry skin. Notice lack of movement. Smell the tank. Check for mites. Observe behavior. Avoid confusion with molting.