Rats are nocturnal by nature. This means that they hunt by night and prefer to avoid daylight. Rats, as a rule, sleep all day and awaken at dusk to begin their nightly patrols. That is why you hear rats scurrying in the walls and ceiling while you are trying to sleep. Scientists have long wondered how these behavioral patterns work. –Understanding how light or dark depress or stimulate rat activity levels may help us understand how it affects humans too. This research might also be helpful in finding ways to help keep your home and yard free of rats.



Nocturnal creatures have eyes that evolved differently from other animals, human included. A very specific trait they developed enables them to see in the dark or maneuver easily in very dim light. Scientists have observed that all rats, even those with some type of visual defects, react to light. It seems that special cells exist in a rat's eye that contains a substance called melanopsin. They have found that this is a light-detecting protein; it actually sends messages to the brain telling it the degree of brightness that surrounds the rat.

Most organisms, including rats and humans naturally adjust to daily cycle of day and night. Adapting to this inner schedule is essential to our survival. Circadian rhythms describes the roughly 24 hour cycle in almost all beings that governs the action of setting the timing for sleeping and waking, our metabolism, hormone secretion and other bodily functions. Our body’s rhythms are in accord with “clock" genes. These genes automatically set the way our “machinery” runs, especially the way it responds to light. Researchers tested these theories on rats by exposing them to alternating cycles of light and dark. While the rats’ circadian rhythms that prevail over sleep adapted, other functions suffered. Strobe light made the rats slow and unresponsive. Exposing rats to light at night seems to disrupt their normal routines.

When kept under light continuously, they eat at more often and as a result, gain weight. Researchers also believe that rats are more aggressive in the dark due to hormonal fluctuations. Because light stimulates the production of estrogen, a hormone that curbs aggression, rats kept in the light were more sociable. Artificial lights, such as fluorescents, bug lights, and street lamps seem to slow rats desire to forage. This reaction only lasts as long as the rat is in the light. DIY remedies to get rid of rats have long included items like Electronic devices that claim to scare rats by emitting bright flashes or strobe lights. Gardeners sometimes use glittering strips of Mylar or tin foil to frighten rats off fruit and vegetable crops. Researchers hope that further studies on this subject will not only reveal more about human nature, but also help to discover new ways to control nuisance rats.

Read the How to get rid of rats page for helpful information and to learn more about Do rats come out in light / avoid light?

Do rats come out in light / avoid light?