Great apes — gorillas, chimpanzees, bonobos and orangutans — are our closest primate relatives, and all are known to carry their young on their backs. In most primate species, newborns are unable to walk or care for themselves, and are not protected by nests. Their slow development requires that their mothers keep them close, for frequent nursing and for transportation and protection. Infants are usually transferred from the front of the mother’s body to her back when they are strong enough to grip her securely — typically when they are few months old, according to a study published April 2008 in the journal Naturwissenschaften.
Chimpanzees are the most social of the great apes, and they also demonstrate a long period of dependency between mothers and offspring. Infants nurse for up to five years, and frequently stay close to their mothers for several more years after they are fully weaned, according to the nonprofit conservation organization Center for Great Apes.
2. Wolf spider
Wolf spiders practice a form of infant care that is unique among spiders. As soon as the spiderlings emerge from their egg sac, they immediately clamber onto their mother’s back, where they remain for up to two weeks, researchers reported in a study of several wolf spider species, published in 1964 in the journal Arkansas Academy of Science Proceedings.
The scientists observed that the first spiderling usually hesitated as it poked its head out of a hole in the egg sac. But it soon scrambled out, crawling over its mother’s body until it settled on her back, and all of its siblings followed shortly thereafter and crowded aboard. As many as 1,035 spiderlings piled on in the wolf spider species Lycosa rabida, the scientists discovered.
Once the spiderlings were settled on their mother’s back, the scene could be quite chaotic, according to the researchers.
“The egg sacs usually emptied within 3 hours, and the spiderlings have stacked themselves on top of each other over the “mother’s” abdomen, and may be spilling over onto the sides and onto her phalothorax — which keeps her busy, occasionally, brushing them out of her eyes with her palpi,” the study authors wrote.
3. Giant anteater
For the first year of their lives, giant anteater young — known as “pups” — frequently ride on their mothers’ backs, according to a species description published online by the San ᴅɪᴇgo Zoo.
Giant anteaters (Myrmecophaga tridactyla),usually bear one pup at a time. Newborns weigh about three pounds (1.4 kilograms) at birth and emerge covered in a full coat of hair. They stick close by their mothers for four weeks, nestling under her to nurse and clambering up onto her back for a lift whenever she moves around. Pups grow more independent after about one month, but are still frequent passengers on their mothers’ backs, the San ᴅɪᴇgo Zoo explains, adding that the pups will usually wean by the time they are nine months old, and leave their mothers at about two years old, when they are s.ᴇ xually mature.
4. Surinam toad
The grey, tongueless, triangle-headed and curiously flat Surinam toad (Pipa pipa) is almost entirely aquatic, living in lowland rainforests in Bolivia, Brazil, Colombia, Ecuador, the Guianas, Peru and Trinidad.
During mating season, the male helps the female to position up to 100 ꜰᴇʀᴛɪʟɪᴢᴇd eggs on her back, where they are overgrown by skin, according to the Encyclopedia of Life. While encased in her back, the embryos develop within the eggs as tadpoles for around three to four months, finally bursting out of the mother’s back as tiny froglets that measure about 0.8 inches (2 centimeters) in length. After the leggy little ones emerge, the mother sheds her skin in preparation for the next mating season, the San ᴅɪᴇgo Zoo explained in a species description.
Swans, the world’s largest waterfowl, are widely recognized for their loyalty to their mates and are known to pair up for life. But swan mothers have also been observed providing especially devoted attention to their young — known as cygnets — by serving as a temporary flotation device to help the little ones as they learn to swim.
Of the six knowns swan species, orange-billed mute swans (Cygnus olor) are the most common sight, visible in ponds and lakes in Europe, northern-central Asia and in North America, where they were introduced in the late 19th century. They were brought to the U.S. as “decorative” birds in zoos, parks and private estates, but feral populations spread to the Northeast, Mid-Atlantic, Great Lakes, and Pacific Northwest regions, according to the Cornell Lab of Ornithology.
Female swans typically lay five to seven eggs, which incubate for 36 to 38 days, according to the University of Michigan Museum of Zoology. Cygnets are covered in white or grayish down, and can swim and dive about 24 hours after hatching. Their mothers and fathers share parental care, frequently carrying the cygnets on their backs, with their wings curled protectively over their babies.
Keeping track of up to 100 babies is a daunting task for any mother, and female scorpions do so by carrying their scores of young — called scorplings — on their backs until the scorplings’ first molt, according to a study published in 2011 in the European Journal of Entomology.
The scorplings are born alive, and their boᴅɪᴇs, which look like tiny versions of adult scorpions’ forms, are soft and pale. They leave their mother’s back after about 10 to 20 days, when their exoskeletons harden and darken.
Scorpion mothers sometimes enjoy an additional benefit from bearing their babies on their backs — easy access to a quick snack. However, this type of cannibalism typically only happens when the mother can’t find any prey, the study authors wrote.
7. Horned marsupial frog
The term “marsupial” typically conjures images of mammals that tote their young in furry pouches, such as kangaroos, koalas, and other denizens of the Australian continent. But the rare and endangered horned marsupial frog (Gastrotheca cornuta), which lives in the forests of Panama, Columbia and Ecuador, also bears a stretchy baby-bearing pouch — on her back.
Inside her pouch, the mother frog incubates a small clutch of the largest known amphibian eggs, which measure about 0.4 inches (10 millimeters) in diameter. To put that into perspective, the mother’s entire body measures about 3 inches (77 mm), herpetologist Jay M. Savage, an adjunct professor of biology at San ᴅɪᴇgo State University, wrote in “The Amphibians and Reptiles of Costa Rica” (The University of Chicago Press, 2002).
After a male ꜰᴇʀᴛɪʟɪᴢᴇs the females’ eggs, he guides them into her pouch, where the embryos develop into froglets. The pouch is a permanent structure, but it changes greatly during reproduction, with separate chambers forming to encase each tiny embryo. It is thought that air circulates to the developing froglets’ gills through a network of veins in the pouch, Savage wrote.