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A new study on what African great apes eat used a near foolproof source: their poop.

The study, published in the latest issue of Scientific Reports, looked at feces taken from three species in the wild: gorillas, chimpanzees and bonobos. Lead author Ibrahim Hamad from Aix-Marseille University and his team used a "DNA-barcoding" method to look for remains of digested food.

The researchers were surprised to find that all three great apes ate a lot of insects, including different types of beetles. "Insects are particularly valuable because they provide certain amino acids, vitamins (such as B12) and minerals (including iron and manganese) that may be absent in plant foods," according to Hamad and his team.

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The researchers mention what other primates eat as well. Medium-bodied primates eat a diet that consists "mainly of young leaves, flowers and unripe fruit," they share. All primates, such as this squirrel monkey, seem to enjoy tender young leaves.

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Several different species of moths were detected in the great ape feces. Moths are plentiful, and must be easy eats for hungry primates. The primates eat butterflies too, according to the study.

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Dozens of different types of flies, including common houseflies, were found in the great ape waste. Flies, as well as their larvae, are low in fat yet high in protein. They can carry germs too, but that doesn't seem to deter primates from eating them.

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Susan Alberts, a Duke University biologist, calls primates "generalists." She explained that they have broad, flexible diets that allow them to adjust to seasonal shortages of their favorite foods. In addition to consuming berries, seeds and nuts, many primates will also eat the bark off of certain trees.

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Termites are so coveted by non-human primates that many have learned how to fish for them with sticks. Here, a bonobo eats termites off of a stick that was used to probe a termite mound. Capuchin monkeys do this too.

As for how the practice started, "It is tempting to believe that a serendipitous discovery was made by one of the members of the group and then other capuchins learned how to do it through observation," Antonio Souto, a researcher in the Department of Zoology at the Federal University of Pernambuco, told Discovery News.

There may be some truth to the old adage: Monkey see, monkey do.

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Every primate seems to love tasty, sweet and ripe fruit. This long-tailed macaque appears to be enjoying a fruit snack.

Some primates eat a lot of unripe fruits too. Hamad and his team mention, for example, that red colobus monkeys and blue monkeys mostly eat unripe fruits -- probably because they can get them before other hungry predators, including insects, do.

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Hamad and his team found evidence for midges and gnats in the primate feces. These insects certainly don't seem palatable, but non-human primates appear to tolerate them as a small, but available, food source. They also likely are eaten incidentally, while primates chomp into a juicy fruit or tender leaf that might have gnats on it.

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Bonobo poop examined in the new study contained remains of digested mosquitoes. While mosquitoes can transmit diseases, the insects do contain some nutrients. Primates may be eating them on purpose, incidentally, or while grooming another.

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Primates love to eat certain flowers, many of which taste sweet. For example, blue borage, also known as starflower, possesses a slightly sweet taste, especially in combination with other vegetation.

Among the surprises in the study -- the tests turned up no sign of ants in the primates' poop, even though they're known to eat them. Also, unlike humans, the animals seem to be eating very little meat, in general.

Next, researchers hope to collect feces during particular seasons to learn how climate and other factors may affect diets.