question: How do animals that live most of their lives underground keep dirt from getting in their eyes?
comment: Absolutely not kidding: eyelids. Yes, there is some hair that blocks, and some behavioral things that also help keep dirt out of their eyes. But in short: eyelids.
passages: The eyes of moles and of some burrowing rodents are rudimentary in size, and in some cases are quite covered by skin and fur. This state of the eyes is probably due to gradual reduction from disuse, but aided perhaps by natural selection. In South America, a burrowing rodent, the tuco-tuco, or Ctenomys, is even more subterranean in its habits than the mole; and I was assured by a Spaniard, who had often caught them, that they were frequently blind. One which I kept alive was certainly in this condition, the cause, as appeared on dissection, having been inflammation of the nictitating membrane. As frequent inflammation of the eyes must be injurious to any animal, and as eyes are certainly not necessary to animals having subterranean habits, a reduction in their size, with the adhesion of the eyelids and growth of fur over them, might in such case be an advantage; and if so, natural selection would aid the effects of disuse. (Charles Darwin, The Origin of Species)
   Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates.
  
  Section::::Types.:Non-compound eyes.:Spherical lens eye.
   Wile E. then tries a vacuum cleaner to suck up the rabbit, getting a dynamite decoy instead (before the decoy explodes, he says, "Well, well, the boy has talent"), a cannon shot, which Bugs re-directs at the Coyote thanks to some underground pipes (Coyote: "But how? Well, even a genius can have an off-day"), and "Quick-Drying Cement". The cement dries into a cylindrical block. As Wile E. laughs, saying, "What a wonderful way to "cement" a friendship.", he runs right into the block, which tips over on top of him. Bugs then pops out and says, "Well, now he has "concrete" evidence that I'm a good neighbor".
   Building materials are gathered near the white-throated woodrat's shelter. At McDowell Mountain Regional Park, Arizona, white-throated woodrats gathered 30% of house building materials within 33 feet (10 m) from their shelter. Houses and dens are altered and refurbished during the year using new and old building materials.
   Lying over the sclera and the interior of the eyelids is a transparent membrane called the conjunctiva. It helps lubricate the eye by producing mucus and tears. It also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye.
  
  In many animals, including humans, eyelids wipe the eye and prevent dehydration. They spread tears on the eyes, which contains substances which help fight bacterial infection as part of the immune system. Some species have a nictitating membrane for further protection.
   Rodent- or bat-proofing buildings by sealing cracks and holes prevents these animals from gaining access to suitable habitats where they are not welcome. Storing seed and pet food in tightly closed containers, controlling weeds and garden debris around homes and buildings, and storing firewood and building supplies on racks or pallets above ground level are also practices that can limit or remove the animals’ sources of food, water or shelter.
  
  Section::::Control methods.:Repellents.
   Blindness in animals
  
  Visual perception in animals plays an important role in the animal kingdom, most importantly for the identification of food sources and avoidance of predators. For this reason, blindness in animals is a unique topic of study.
  
  In general, nocturnal or subterranean animals have less interest in the visual world, and depend on other sensory modalities. Visual capacity is a continuum, with humans falling somewhere in the center.
  
  Section::::Totally blind species.
  
  BULLET::::- Some moles (the star-nosed mole can detect, catch and eat food faster than the human eye can follow; under 300 milliseconds)
   Section::::Animals.:Primates.
  
  There are several hypotheses about the importance of geophagia in bats and primates. Chimpanzees in Kibale National Park, Uganda, have been observed to consume soil rich in kaolinite clay shortly before or after consuming plants including "Trichilia rubescens", which possesses antimalarial properties in the laboratory.
  
  Section::::Animals.:Bats.
   Chipmunks, mice, voles, and shrews eat large quantities of conifer seeds from the forest floor, and clipped cones are a staple and major part of storage of red squirrels. These animals store a large amount of Rocky Mountain Douglas-fir cones or seeds. American marten commonly den in hollow logs.
   In some cases beta, 1-3 glycan synthase is also released to penetrate the callose matrix.
  
  Section::::Plant defences.
   The bottom of the enclosure, if it is not the ground or trays of dirt, needs be a surface more solid than screening. A snail placed in a wire-mesh-bottom pen will keep crawling, trying to get off the wires and onto solid, more comfortable ground.
   Bugs wakes up after a long night to find that a burly construction worker (whom Bugs derisively dubs "Hercules") has just shoveled up his rabbit hole near a highrise building being built. Bugs kindly asks Hercules to put his hole back, and Hercules pretends to comply, before he dumps Bugs and the dirt into the dump truck. Bugs angrily shouts "Hey, you big gorilla! Didn't you ever hear of the sanctity of the American home?" before another mound of earth falls on him and the truck hauls him away.
   In humans, the eyebrows redirect flowing substances (such as rainwater or sweat) away from the eye.
  
  Section::::Function of the mammalian eye.
  
  The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain.
   North American badgers ("Taxidea taxus") hunt Richardson's ground squirrels ("Spermophilus richardsonii"). The most common hunting technique is excavation of burrow systems, but plugging of openings into ground-squirrel tunnels accounts for 5–23% of hunting actions. Badgers usually use soil from around the tunnel opening, or soil dragged 30–270 cm from a nearby mound to plug tunnels. The least common (6%), but most novel, form of plugging used by 1 badger involved movement of 37 objects from distances of 20–105 cm to plug openings into 23 ground-squirrel tunnels on 14 nights.
   Another likely explanation for the loss of its eyes is that of selective neutrality and genetic drift; in the dark environment of the cave, the eyes are neither advantageous nor disadvantageous and thus any genetic factors that might impair the eyes (or their development) can take hold with no consequence on the individual or species. Because there is no selection pressure for sight in this environment, any number of genetic abnormalities that give rise to the damage or loss of eyes could proliferate among the population with no effect on the fitness of the population.
   Section::::Nitrogen fixation.
  
  "G. sulphureus" is able to fix nitrogen. An experiment in Thailand found that they fix around 250 grams of nitrogen per hectare per year. Although this contribution is only between 7% and 22% of the total nitrogen inputs in the ecosystem it is thought to be relatively important as termites add it to dead wood, thereby accelerating its decomposition.
  
  Section::::Foraging.
  
  "G. sulphureus" forages areas of up to 62m and ventures up to 16m away from its nest.
  
  Section::::Control.
   Special attention should be paid to the ears of the Bernese Mountain Dog, as they can trap bacteria, dirt, and liquid. The risk of an ear infection drops with weekly ear cleanings using a veterinarian-recommended cleanser.
  
  Section::::Notable Bernese Mountain Dogs.
  
  BULLET::::- Hercules is Pittsburgh Steelers quarterback Ben Roethlisberger's dog that he brought home from the Emmental region of Switzerland during a 2006 weeklong trip to discover his family's roots in the country.
   In the wild, mandrills have been observed to clean their ears with modified tools. Scientists filmed a large male mandrill at Chester Zoo stripping down a twig, apparently to make it narrower, and then using the modified stick to scrape dirt from underneath its toenails.
   Section::::Habitat and conservation.
   Setts are not always excavated entirely in soil. Sometimes they are under the shelter of a shed, or in a pile of timber or rocks. Badgers also excavate them under man-made structures like building foundations, concrete sidewalks, and paved roadways. This can lead to subsidence, and other damage to such structures.
   Octopuses deliberately place stones, shells and even bits of broken bottle to form a wall that constricts the aperture to the den, a type of tool use.
  
  In laboratory studies, "Octopus mercatoris", a small pygmy species of octopus, has been observed to block its lair using a plastic Lego brick.
  
  Smaller individuals of the common blanket octopus ("Tremoctopus violaceus") hold the tentacles of the Portuguese man o' war, to whose poison they are immune, both as protection and as a method of capturing prey.
  
  Section::::In invertebrates.:Insects.
   The "Orthoporus ornatus" enjoys staying in the deep damp soil of a desert ecosystem. The thought of an organism living underground might sound a bit unrealistic. However, the soil is full of honey-comb channels and voids. Not only is the soil full of this millipede's main food source, it also works as protection. Staying underground provides for a safe refuge from any harmful biotic or abiotic events, for example protection from solar ultraviolet radiation.
  
  Section::::Behavior.
   There is little known about the medical importance of "N. orbicollis". Their ability to recycle dead, decomposing matter plays an indirect role in the health of the areas it inhabits. Natural antibiotics secreted by this beetle could potentially be medically beneficial in the future but currently nothing is known about the method of secretion.
  
  Section::::Scientific importance.:Forensic.
   The three main vulnerabilities against the sand are through the eyes, ears, and nose. To keep sand out of their eyes, xerocoles including reptiles and birds, and some amphibians and mammals have a nicitating membrane in their eyes: a third, transparent eyelid that protects the cornea from blowing sand and can dislodge it from the eye. Reptiles also have eyes the size of pinholes or protected by valves. To keep sand out of their ears, mammals such as the camel and the sand cat have long hairs protruding from them. The camel and the saiga antelope also have adaptations to protect their noses from sand: the former has narrow nostrils it can close, and the latter has a large nose with its nostrils set wide apart and far back to prevent sand from entering when grazing. Reptile diggers have nostrils that face upwards instead of forwards for the same reason.
   APOPO has trained Southern giant pouched rats to communicate to humans the presence of land mines, by scratching the ground, and tuberculosis in medical samples. They identify 40% more cases of tuberculosis than clinics do, an extra 12,000 cases from 2007-2017. They have identified 100,000 mines from 2003-2017, certifying 2,200 hectares (5,400 acres) as mine-free. They are accurate enough that the human trainers run on the land after removing the mines which rats have identified.
  
  Rats (Wistar, "Rattus norvegicus") have been taught to distinguish and respond differently to different human faces.
  