Fish
The one-horned rhinofish inhabits tropical seas from the Red Sea to the coast of Japan. It prefers serene waters, reefs, and lagoons. The rhinoceros is peaceful by nature, feeds on bottom algae, and can reach up to 70 centimeters in length. Not all individuals have a horn on the forehead, and it does not grow in young animals. The horn is hard bone, but scientists have not pinpointed its purpose. One idea is that it reduces resistance while swimming, though there is no solid evidence. Rhinofish are edible and prized for their tough skin, which ancient Hawaiians used to stretch over drums.
In contrast, the swordfish possesses a functional horn. Unlike the rhinoceros, it is an active predator that can grow up to 4.5 meters. The horn extends from the upper jaw, not the forehead. It is often assumed the long protrusion acts as a spear to pierce prey at high speeds, but the speed is not how it works. Instead the sword functions like a blade that cuts through fish. Researchers also suggest the tip may serve a defensive role against larger predators.
Insects
The rhinoceros beetle is among the largest insects in Europe, reaching up to 4.5 centimeters in length. This species lives on wood, and the larvae develop in rotted logs. In urban areas, rhinoceros beetles have adapted to thrive in rotted manure or garbage heaps as long as plant debris is plentiful. The larval stage lasts two to four years, while the adult lives only a few months. As an adult, the beetle does not feed and relies on reserves accumulated during the larval period.
Only males bear a prominent horn, while females carry a much smaller one. In healthy males, the horn is long, curved, and pointed, giving the insect a rhinoceros-like profile. The horn aids in deterring rivals during mating, typically by driving them away from females. Horn size depends on hormonal signals linked to nutrition and stress; starved or poorly healthy insects may not develop large horns. Females use their horns in mate selection, guiding them to suitable partners.
Snakes
The rhinoceros viper features a horn that grows on its nose. This venomous snake can reach up to 1.2 meters and is native to equatorial Africa. It is mainly nocturnal, seeking shelter during the day in leaf litter, burrows, fallen trees, or forest roots. It can climb thanks to a prehensile tail.
The horn or horns on these snakes are formed from scales and are not very hard. The exact function remains unclear, though scientists suspect it helps blur the snake’s silhouette on the forest floor, aiding ambush hunting. Other snake species around the world show similar but less pronounced snout protrusions. Given diverse habitats, such horns likely evolved independently for different reasons, such as eye protection when buried in sand in deserts, though this idea is debated.
Whales
The narwhal, once thought to be a unicorn of the sea, is a member of the cetacean suborder along with dolphins. Narwhals inhabit northern waters, growing up to about 4.5 meters and weighing as much as three tonnes. They feed on cephalopods and bottom fish, and the tusk plays a role in prey manipulation as it helps push prey away from sediment.
Biologically, the horn is a tusk, a modified tooth, most often the left tooth with the right one hidden inside the head. Males develop a tusk, and females sometimes possess a shorter version. The exact purpose puzzles zoologists. The horn appears fragile yet is highly flexible. It was once hypothesized to function like a peacock’s tail for mating displays and status signaling, but field observations have not supported this idea. Modern drone footage has clarified that the tooth does not stun Arctic cod during feeding.
Additionally, the horn contains numerous nerve endings, providing environmental feedback. Narwhals sometimes break through ice to breathe, revealing the horn’s sensory role in navigation and hunting.
Birds
Hornbills comprise a large family found in Africa and southern Asia, with many genera. Some species feature pronounced beak shields or helmets that resemble horns. The Malayan kalao, for example, shows a helmet that can lie close to the beak or be raised above it.
The red-billed hornbill has a smaller crown-like growth. The exact function of these horns remains a mystery to biologists. Their hollow structure makes them light and unlikely to be weapons; they likely act as resonators to amplify vocalizations. In contrast, the helmet-like horn of the kalao is bone and can be used in aerial battles for territory. Some hornbill species, such as the southern yellow-billed lek, lack horns altogether.
Across many horn-bearing species, scientists remain uncertain about the horn’s purpose. For narwhals, the horn does not seem vital for survival. Even among rhinoceroses, horns serve multiple roles beyond combat, including display, digging, guiding offspring, or marking territory. It is important to note that several rhinoceros species are endangered, underscoring the need for conservation.