Zebra stripes stop flies carrying deadly diseases from landing on them, research shows
Scientists place sheets on horses to test theory
It has puzzled them since the days of Charles Darwin, but now scientists have established why Zebras have stripes - and it's not just for looks. They also stop blood-sucking flies from landing on the animal and protect them from deadly diseases, according to new research.
To test the theory they put striped coats on horses and found that fewer flies landed on them, than when they wore single-colour coats.
“We showed that horse flies approach zebras and uniformly coloured horses at similar rates but that they fail to land on zebras – or striped horse coats – because they fail to decelerate properly,” said behavioural ecologist Tim Caro, who led the research which was published in the journal PLOS ONE.
The insects either flew past or bumped into them and bounced off, he added.
Previous theories have suggested stripes evolved in zebras because they helped with temperature regulation, camouflaged them from predators or performed a social function, such as individual recognition.
Wildlife photographer of the year
Show all 25
Wildlife photographer of the year
1/25 Curious Encounter - Shortlisted
Cristobal Serrano, Spain. Any close encounter with an animal in the vast wilderness of Antarctica happens by chance, so Cristobal was thrilled by this spontaneous meeting with a crabeater seal off of Cuverville Island, Antarctic Peninsula. These curious creatures are protected and, with few predators, thrive.
2/25 Bond of brothers - Winner
David Lloyd, New Zealand / UK.
These two adult males, probably brothers, greeted and rubbed faces for 30 seconds before settling down. Most people never have the opportunity to witness such animal sentience, and David was honoured to have experienced and captured such a moment.The picture was taken in Ndutu, Serengeti, Tanzania.
David Lloyd / Natural History Museum
3/25 Fox meets fox - Highly Commended
Matthew Maran, UK.
Matthew has been photographing foxes close to his home in north London for over a year and ever since spotting this street art had dreamt of capturing this image. After countless hours and many failed attempts his persistence paid off.
Matthew Maran / Natural History Museum
4/25 Three Kings - Highly Commended
Wim Van Den Heever, South Africa.
Wim came across these king penguins on a beach in the Falkland Islands just as the sun was rising. They were caught up in a fascinating mating behaviour –the two males were constantly moving around the female using their flippers to fend the other off.
Wim Van Den Heever / Natural History Museum
5/25 A polar bear's struggle - Highly Commended
Justin Hofman, USA.
Justin’s whole body pained as he watched this starving polar bear at an abandoned hunter's camp, in the Canadian Arctic, slowly heave itself up to standing. With little, and thinning, ice to move around on, the bear is unable to search for food.
Justin Hofman / Natural History Museum
6/25 One toy, three dogs - Highly Commended
Bence Mate, Hungary.
While adult African wild dogs are merciless killers, their pups are extremely cute and play all day long. Bence photographed these brothers in Mkuze, South Africa –they all wanted to play with the leg of an impala and were trying to drag it in three different directions!
Bence Mate / Natural History Museum
7/25 Clam Close-up - Shortlisted
David Barrio, Spain. This macro-shot of an iridescent clam was taken in the Southern Red Sea, Marsa Alam, Egypt. These clams spend their lives embedded amongst stony corals, where they nest and grow. It took David some time to approach the clam, fearing it would sense his movements and snap shut!
8/25 The Orphaned Beaver - Shortlisted
Suzi Eszterhas, United States. A one-month-old orphaned North American beaver kit is held by a caretaker at the Sarvey Wildlife Care Center in Arlington, Washington. Luckily it was paired with a female beaver who took on the role of mother and they were later released into the wild.
Photo by Suzi Eszterhas
9/25 Ice and Water - Shortlisted
Audun Lie Dahl, Norway. The Bråsvellbreen glacier moves southwards from one of the ice caps covering the Svalbard Archipelago, Norway. Where it meets the sea, the glacier wall is so high that only the waterfalls are visible, so Audun used a drone to capture this unique perspective
10/25 Teenager - Shortlisted
Franco Banfi, Switzerland. Franco was free diving off Dominica in the Caribbean Sea when he witnessed this young male sperm whale trying to copulate with a female. Unfortunately for him her calf was always in the way and the frisky male had to continually chase off the troublesome calf.
11/25 Resting Mountain Gorilla - Shortlisted
David Lloyd. The baby gorilla clung to its mother whilst keeping a curious eye on David. He had been trekking in South Bwindi, Uganda, whenhe came across the whole family. Following them, they then stopped in a small clearing to relax and groom each other.
12/25 Painted Waterfall - Shorltisted
Eduardo Blanco Mendizabal, Spain. When the sun beams through a hole in the rock at the foot of the La Foradada waterfall, Catalonia, Spain, it creates a beautiful pool of light. The rays appear to paint the spray of the waterfall and create a truly magical picture.
13/25 The Extraction - Shortlisted
Konstantin Shatenev, Russia. Every winter, hundreds of Steller's sea eagles migrate from Russia, to the relatively ice-free northeastern coast of Hokkaido, Japan. They hunt for fish among the ices floes and also scavenge, following the fishing boats to feed on any discards. Konstantin took his image from a boat as the eagles retrieved a dead fish thrown onto the ice.
14/25 Shy - Shortlisted
Pedro Carrillo, Spain. The mesmerizing pattern of a beaded sand anemone beautifully frames a juvenile Clarkii clownfish in Lembehstrait, Sulawesi, Indonesia. Known as a 'nursery' anemone, it is often a temporary home for young clownfish until they find a more suitable host anemone for adulthood.
15/25 Red, Silver and Black - Shortlisted
TinMan Lee, USA. Tin was fortunate enough to be told about a fox den in Washington State, North America, which was home to a family of red, black and silver foxes. After days of waiting for good weather he was finally rewarded with this touching moment.
16/25 Isolated - Shortlisted
Anna Henly, UK. Snapped from a helicopter, this isolated tree stands in a cultivated field on the edge of a tropical forest on Kauai, Hawaii. The manmade straight lines of the ploughed furrows are interrupted beautifully by nature’s more unruly wild pattern of tree branches.
17/25 Sound Asleep - Shortlisted
Tony Wu, USA. This adult humpback whale balanced in mid-water, headon and sound asleep was photographed in Vava’u, Kingdom of Tonga. The faint stream of bubbles, visible at the top, is coming from the whale’s two blowholes and was, in this instance, indicative of an extremely relaxed state.
18/25 All That Remains - Shortlisted
Phil Jones, UK. A male orca had beached itself about a week before Phil’s visit to Sea Lion Island, Falkland Islands. Despite its huge size the shifting sands had almost covered the whole carcass and scavengers, such as this striated caracara, had started to move in.
19/25 Ambush - Shortlisted
Federico Veronesi, Kenya. On a hot morning at the Chitake Springs, in Mana Pools National Park, Zimbabwe, Federico watched as an old lioness descended from the top of the riverbank. She’d been lying in wait to ambush any passing animals visiting a nearby waterhole further along the riverbed.
20/25 Gliding - Shortlisted
Christian Vizl, Mexico. With conditions of perfect visibility and beautiful sunlight, Christian took this portrait of a nurse shark gliding through the ocean off the coast of Bimini in the Bahamas. Typically these sharks are found near sandy bottoms where they rest, so it’s rare to see them swimming.
21/25 Otherworldly - Shortlisted
Franco Banfi, Switzerland. A school of Munk's devil ray were feeding on plankton at night off the coast of Isla Espíritu Santo in Baja California, Mexico. Franco used the underwater lights from his boat and a long exposure to create this otherworldly image.
22/25 The Bat’s Wake - Shortlisted
Antonio Leiva Sanchez, Spain. After several months of field research into a little colony of greater mouse-eared bats in Sucs, Lleida, Spain, Antonio managed to capture this bat mid-flight. He used a technique of high speed photography with flashes combined with continuous light to create the ‘wake’.
23/25 Under the Snow - Shortlisted
Audren Morel, France. Unafraid of the snowy blizzard, this squirrel came to visit Audren as he was taking photographs of birds in the small Jura village of Les Fourgs, France. Impressed by the squirrel’s endurance, he made it the subject of the shoot.
24/25 Unique Bill - Shortlisted
Rob Blanken, The Netherlands. The pied avocet has a unique and delicate bill, which it sweeps like a scythe, as it sifts for food in shallow brackish water. This stunning portrait was taken from a hide in the northern province of Friesland in The Netherlands.
25/25 Family Portrait - Shortlisted
Connor Stefanison, Canada. A great grey owl and her chicks sit in their nest in the broken top of a Douglas fir tree in Kamloops, Canada. They looked towards Connor only twice as he watched them during the nesting season from a tree hide 50 feet (15 metres) up.
1/25 Curious Encounter - Shortlisted
Cristobal Serrano, Spain. Any close encounter with an animal in the vast wilderness of Antarctica happens by chance, so Cristobal was thrilled by this spontaneous meeting with a crabeater seal off of Cuverville Island, Antarctic Peninsula. These curious creatures are protected and, with few predators, thrive.
2/25 Bond of brothers - Winner
David Lloyd, New Zealand / UK.
These two adult males, probably brothers, greeted and rubbed faces for 30 seconds before settling down. Most people never have the opportunity to witness such animal sentience, and David was honoured to have experienced and captured such a moment.The picture was taken in Ndutu, Serengeti, Tanzania.
David Lloyd / Natural History Museum
3/25 Fox meets fox - Highly Commended
Matthew Maran, UK.
Matthew has been photographing foxes close to his home in north London for over a year and ever since spotting this street art had dreamt of capturing this image. After countless hours and many failed attempts his persistence paid off.
Matthew Maran / Natural History Museum
4/25 Three Kings - Highly Commended
Wim Van Den Heever, South Africa.
Wim came across these king penguins on a beach in the Falkland Islands just as the sun was rising. They were caught up in a fascinating mating behaviour –the two males were constantly moving around the female using their flippers to fend the other off.
Wim Van Den Heever / Natural History Museum
5/25 A polar bear's struggle - Highly Commended
Justin Hofman, USA.
Justin’s whole body pained as he watched this starving polar bear at an abandoned hunter's camp, in the Canadian Arctic, slowly heave itself up to standing. With little, and thinning, ice to move around on, the bear is unable to search for food.
Justin Hofman / Natural History Museum
6/25 One toy, three dogs - Highly Commended
Bence Mate, Hungary.
While adult African wild dogs are merciless killers, their pups are extremely cute and play all day long. Bence photographed these brothers in Mkuze, South Africa –they all wanted to play with the leg of an impala and were trying to drag it in three different directions!
Bence Mate / Natural History Museum
7/25 Clam Close-up - Shortlisted
David Barrio, Spain. This macro-shot of an iridescent clam was taken in the Southern Red Sea, Marsa Alam, Egypt. These clams spend their lives embedded amongst stony corals, where they nest and grow. It took David some time to approach the clam, fearing it would sense his movements and snap shut!
8/25 The Orphaned Beaver - Shortlisted
Suzi Eszterhas, United States. A one-month-old orphaned North American beaver kit is held by a caretaker at the Sarvey Wildlife Care Center in Arlington, Washington. Luckily it was paired with a female beaver who took on the role of mother and they were later released into the wild.
Photo by Suzi Eszterhas
9/25 Ice and Water - Shortlisted
Audun Lie Dahl, Norway. The Bråsvellbreen glacier moves southwards from one of the ice caps covering the Svalbard Archipelago, Norway. Where it meets the sea, the glacier wall is so high that only the waterfalls are visible, so Audun used a drone to capture this unique perspective
10/25 Teenager - Shortlisted
Franco Banfi, Switzerland. Franco was free diving off Dominica in the Caribbean Sea when he witnessed this young male sperm whale trying to copulate with a female. Unfortunately for him her calf was always in the way and the frisky male had to continually chase off the troublesome calf.
11/25 Resting Mountain Gorilla - Shortlisted
David Lloyd. The baby gorilla clung to its mother whilst keeping a curious eye on David. He had been trekking in South Bwindi, Uganda, whenhe came across the whole family. Following them, they then stopped in a small clearing to relax and groom each other.
12/25 Painted Waterfall - Shorltisted
Eduardo Blanco Mendizabal, Spain. When the sun beams through a hole in the rock at the foot of the La Foradada waterfall, Catalonia, Spain, it creates a beautiful pool of light. The rays appear to paint the spray of the waterfall and create a truly magical picture.
13/25 The Extraction - Shortlisted
Konstantin Shatenev, Russia. Every winter, hundreds of Steller's sea eagles migrate from Russia, to the relatively ice-free northeastern coast of Hokkaido, Japan. They hunt for fish among the ices floes and also scavenge, following the fishing boats to feed on any discards. Konstantin took his image from a boat as the eagles retrieved a dead fish thrown onto the ice.
14/25 Shy - Shortlisted
Pedro Carrillo, Spain. The mesmerizing pattern of a beaded sand anemone beautifully frames a juvenile Clarkii clownfish in Lembehstrait, Sulawesi, Indonesia. Known as a 'nursery' anemone, it is often a temporary home for young clownfish until they find a more suitable host anemone for adulthood.
15/25 Red, Silver and Black - Shortlisted
TinMan Lee, USA. Tin was fortunate enough to be told about a fox den in Washington State, North America, which was home to a family of red, black and silver foxes. After days of waiting for good weather he was finally rewarded with this touching moment.
16/25 Isolated - Shortlisted
Anna Henly, UK. Snapped from a helicopter, this isolated tree stands in a cultivated field on the edge of a tropical forest on Kauai, Hawaii. The manmade straight lines of the ploughed furrows are interrupted beautifully by nature’s more unruly wild pattern of tree branches.
17/25 Sound Asleep - Shortlisted
Tony Wu, USA. This adult humpback whale balanced in mid-water, headon and sound asleep was photographed in Vava’u, Kingdom of Tonga. The faint stream of bubbles, visible at the top, is coming from the whale’s two blowholes and was, in this instance, indicative of an extremely relaxed state.
18/25 All That Remains - Shortlisted
Phil Jones, UK. A male orca had beached itself about a week before Phil’s visit to Sea Lion Island, Falkland Islands. Despite its huge size the shifting sands had almost covered the whole carcass and scavengers, such as this striated caracara, had started to move in.
19/25 Ambush - Shortlisted
Federico Veronesi, Kenya. On a hot morning at the Chitake Springs, in Mana Pools National Park, Zimbabwe, Federico watched as an old lioness descended from the top of the riverbank. She’d been lying in wait to ambush any passing animals visiting a nearby waterhole further along the riverbed.
20/25 Gliding - Shortlisted
Christian Vizl, Mexico. With conditions of perfect visibility and beautiful sunlight, Christian took this portrait of a nurse shark gliding through the ocean off the coast of Bimini in the Bahamas. Typically these sharks are found near sandy bottoms where they rest, so it’s rare to see them swimming.
21/25 Otherworldly - Shortlisted
Franco Banfi, Switzerland. A school of Munk's devil ray were feeding on plankton at night off the coast of Isla Espíritu Santo in Baja California, Mexico. Franco used the underwater lights from his boat and a long exposure to create this otherworldly image.
22/25 The Bat’s Wake - Shortlisted
Antonio Leiva Sanchez, Spain. After several months of field research into a little colony of greater mouse-eared bats in Sucs, Lleida, Spain, Antonio managed to capture this bat mid-flight. He used a technique of high speed photography with flashes combined with continuous light to create the ‘wake’.
23/25 Under the Snow - Shortlisted
Audren Morel, France. Unafraid of the snowy blizzard, this squirrel came to visit Audren as he was taking photographs of birds in the small Jura village of Les Fourgs, France. Impressed by the squirrel’s endurance, he made it the subject of the shoot.
24/25 Unique Bill - Shortlisted
Rob Blanken, The Netherlands. The pied avocet has a unique and delicate bill, which it sweeps like a scythe, as it sifts for food in shallow brackish water. This stunning portrait was taken from a hide in the northern province of Friesland in The Netherlands.
25/25 Family Portrait - Shortlisted
Connor Stefanison, Canada. A great grey owl and her chicks sit in their nest in the broken top of a Douglas fir tree in Kamloops, Canada. They looked towards Connor only twice as he watched them during the nesting season from a tree hide 50 feet (15 metres) up.
The idea that stripes help zebras thwart biting flies has previously been suggested and Mr Caro said it was the only one that "stands up to scrutiny."
He added: "Most biologists involved with research on mammal colouration accept that this is the reason that zebras have stripes."
African horse flies carry diseases such as trypanosomiasis and African horse sickess, which can cause wasting and can be fatal.
“We think there’s a real strong selective pressure against being bitten because it could be a matter of life or death,” University of Bristol biologist and the study's co-author Martin How Dr Martin How told BBC Radio 4’s Today programme.
Researchers recorded horse flies as they attempted to prey on captive zebras and domestic horses at a livery in North Somerset, England.
Although stripes did not deter flies from a distance, they landed on zebras less than a quarter as often as they did on horses.
Zebras are close cousins to horses and donkeys and their distinctive stripe patterns are unique to each individual.
The research could also be useful for humans who want to avoid being bitten by some insects.
“We found that while we were doing our research, if we wore dark black clothing we tended to get attacked far more often by the horse flies than if we wore stripes,” Dr How said.
In addition to their stripes, zebras exhibited more preventative behaviour towards horse flies, such as running away or tail swishing at a far higher rate than horses.
"Zebras are constantly swishing their tail and may run off if horse flies do land successfully, so they are also using behavioural means to prevent flies probing for blood," Mr Caro said.
The researchers are now conducting tests to see what it is exactly about stripes that stops flies, by testing coats with different patterns, contrasts and thickness.
Agencies contributed to this report
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