So assuming in this context you mean civilized to mean that a species has a civilization, it would be ants. Ants parallel humans in a remarkable number of ways. First of all, they have a strict hierarchy of different ants performing different functions, with the queen being the most important. Some ants will gather food, others will fight, and some will even make bridges out of their bodies for other ants to cross! However, one of the most remarkable facts about ants is that they are the only other species that has agriculture. There is a type of ant called the leaf-cutter ant that gathers leaves to feed to a fungus in the anthill. So the same way we plant seeds and water them, ants will gather leaves which will help to feed the fungus. Then the ants will eat the fungus. This way, the ants don’t need to hunt, they can just eat their own home-grown food. Also, some ants domesticate smaller bugs called aphids. They protect the aphids and in return, the aphids secrete a sugary substance called honeydew which feeds the ants. In a sense, they milk the aphids like cows so that they have a steady source of food.

Ant colonies can be a few dozen ants to millions of ants which is like the difference between a small tribe and huge city like Los Angeles. Ants also go to war with different ants and the strategy can be as complex as a modern human warfare. Some people have even gone as far as to say that ants are the dominant species since there are so many of them and they live everywhere.

This might be a matter of opinion based on how you define "civilized." There are many animals that have highly complex social groups that work together such as bees; other groups of animals such as primates and some birds will use tools to take their work easier.

Civilization is a complex idea that includes urban development, symbolic communication (like writing), social stratification, and perception of a separation from nature. Humans are the only species to think of themselves as separate from nature. If we consider that all these qualities are necessary for a species to be considered civilized, then humans are the only species that have civilizations. But, there are animals that have very complex and interesting social structures, like chickens or bees.

Probably honeybees - in fact, I might suggest that honeybees are more civilized than humans. They have competition, though: there are a lot of other ants and bees that are also pretty civilized.

This is a great question that is difficult to answer. We usually define “civilization” using human terms (shared language, organized settlements, social pursuits like science and art, etc.) so it isn’t really fair to ask other species to be “civilized”. Do termite mounds or bee hives count as organized settlements? Does whale or bird song count as language? Does elephant parents playing “peek-a-boo” with their children count as social play? Scientists are actively trying to answer these questions.

For a long time, scientists thought of other animal species as less civilized, social and intelligent because they were looking for human-like behavior in these animals. It was difficult for scientists to imagine how animal species perceive and interact with their environment differently. Many of the evaluations that they gave animals tested them on human skills so, of course, no animal species performed as well as humans. However, more careful observation and better testing has lead us to recognize that many animal species have more complex and “civilized” behavior than we thought.

An important historical example is the case of Clever Hans - a German horse that appeared to count, do arithmetic and other intellectual tasks. When asked a question, Hans would tap his foot in a certain location or to count out the answer, almost always getting it right. “Clever” Hans and his trainer toured Europe, used as an example of how “smart” horses could be. In 1904, a council of scientists concluded that his responses were not faked but did notice that Hans didn’t always get the right answer. In particular, Hans would not answer questions correctly if his trainer didn’t know the answer. (They tested this by asking questions when the trainer was blindfolded and wore ear muffs.) Rather than knowing the answer, Hans was responding to the face of his trainer – he would stamp his foot when the trainer looked encouraging and would stop when he looked worried Hans was about to answer wrong. Many people were disappointed to find that Hans couldn’t do math like they originally thought, thinking that animals were dumb after all.

What do you think? Which is more impressing: answering a math question or reading the emotions of your friend that is another species? As a horse, Hans didn’t care about or understand arithmetic, but pleasing his trainer was important to him.

As scientists are more willing to see the environment from other species’ perspective, they find that animal behavior is just as complex as human behavior. Some people may feel that this makes humans feel less special but, as a scientist, I feel that it makes animal life in general more fascinating. How about you? If you are interested in how animals think and behave, I recommend these popular science books:

“Are We Smart Enough to Know How Smart Animals Are?” by Frans de Waal

“Beyond Words: What Animals Think and Feel” by Carl Safina

“Being a Beast: Adventures Across the Species Divide” by Charles Foster