People aren’t just dressing up their horses as zebras for fun, there’s actually some science behind it!
And it all starts with one simple question: why do zebras have stripes?
There has been scientific interest in the function of zebra stripes for over 150 years.
There have been many theories proposed about why zebras developed stripes – protection from predators, thermoregulation, signalling to other zebras and avoidance of biting flies – but only one of these stands up to careful scrutiny.
Camouflage or confusion against predators is unlikely because African lions take down zebra prey disproportionately more than expected, suggesting an absence of a helping effect, and only have trouble distinguishing the striped pattern from a distance.
The stripes also don’t have a greater effect on grooming patterns of association and there are no thermoregulatory benefits to striping based on controlled experiments.
Averting attack by biting flies is increasingly seen as the evolutionary driver of zebras developing their stripes.
In Africa, horseflies carry diseases fatal to zebras.
This includes trypanosomiasis, equine infectious anaemia, African horse sickness and equine influenza.
Zebras are particularly susceptible to infection because of their thin fur, which allows flies to successfully bite.
The exact mechanism by which the stripes prevent the flies from obtaining a blood meal is not completely understood.
The study, Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses, looked at captive plains zebras and uniformly coloured domestic horses side by side.
They placed the horses and zebras in fields with no protection from the flies and used video analysis to observe the behaviour of the flies around each animal.
The results showed that the flies had significantly fewer successful landings on the zebra.
The video footage showed that the flies seemed to suffer from visual impairment immediately before landing on the striped coat of the zebra.
This problem with their vision resulted in a lot of flies bumping into the zebra or simply flying over it, rather than land.
This image shows that there’s a clear difference in the flight patterns of the flies compared on different coloured horses and zebras:
To rule out other variables in the first experiment, they ran the experiment again, but this time the horse wore a cloth mimicking the striped pattern of the zebra.
This helped to rule out variables such as preferences in the animals’ smell or taste.
And the results were clear; the horse got around 25% fewer flies landing on it than horses wearing a single coloured rug.
Fewer landings also meant fewer flies stayed on the animal to look for a place to bite.
The researchers observed that fewer flies landed on the zebras than on the horses, though the number of flies circling around or briefly touching the fur of horses and zebras didn’t differ.
In an experiment where the horses sequentially wore cloth coats of different colours, those wearing a striped pattern suffered far lower rates of flies touching and landing on the coats when compared to horses wearing black or white.
The number of flies attacking the naked heads of the horses remained the same regardless of what blanket they wore.
In detailed video analysis, the flies approached the zebras faster than they did horses and failed to slow down before making contact with the zebra, resulting in more flies simply bumping off rather than landing on the zebra.
The researchers concluded that, up close, striped surfaces prevents flies from making a controlled landing, though the stripes don’t influence the flies’ behaviour at a distance.
To counteract flies, the zebras would also swish their tails and run away from the nuisance, whereas horses showed a higher rate of skin twitching.
As a consequence of the zebras’ striping, very few flies successfully landed on them, and as a result of their changeable behaviour, few flies stayed very long on probed for blood.
If you’ve got a problem with biting flies, it’s worth the investment to get a striped bug rug for your horse!
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