The equines in a paddock located in North Somerset were outfitted as zebras, causing the horseflies to struggle. That was the aim. Tim Caro, Martin How, and their team investigated tabanid horseflies at a livery yard in North Somerset, documenting their efforts to alight on captive plains zebras and standard domestic horses housed in the same pens. Their findings, published in PLOS ONE in 2019, were straightforward. Flies circled both zebras and horses at similar frequencies, but landed on zebras less than a quarter as often.<\/p>\n
Circling is cost-effective, so the team implemented a more controlled version. Each horse donned a black coat, followed by a white one, then a striped option, in succession. Landings decreased dramatically with the striped coat. On the animal\u2019s bare head, which remained uncovered the entire time, there was no change.<\/p>\n
## Why the flies keep missing<\/p>\n
Slow-motion footage provided the explanation. Horseflies approached zebras rapidly and failed to slow down, either colliding with them or skimming past instead of landing. Caro, quoted in a University of Bristol announcement, noted that the flies \u201cseem to fly over zebra stripes or bump into them.\u201d Such incidents did not occur around the unstriped horses. Stripes do not operate in isolation, either: the same study notes zebras constantly swishing their tails during fly season, ensuring a fly that lands seldom remains long enough to feed.<\/p>\n
The effect is noticeable up close, during the final approach; stripes did not prevent the flies from arriving initially.<\/p>\n
## The lion theory was tested, and it lost<\/p>\n
For nearly a century, the prevalent theory involved predators: stripes disrupting a zebra\u2019s outline in open terrain, or blinding a lion mid-chase. This concept was always perceived through human lenses.<\/p>\n
Amanda Melin, a biological anthropologist from Calgary, collaborated with Caro to analyze zebra images through spatial and color filters replicating the visual systems of lions and spotted hyenas. In a publication in PLOS ONE, they stated that beyond approximately 50 meters in daylight and 30 meters at twilight, large carnivores cannot distinguish the stripes. On moonless nights, visibility drops to about nine meters. A lion close enough to discern stripes is already too close for the stripes to matter.<\/p>\n
Cooling also failed as a viable explanation. G\u00e1bor Horv\u00e1th and his team covered water-filled metal barrels with horse, cattle, and zebra hides, left them outdoors for four months, and continuously recorded their core temperatures. Their research in Scientific Reports found no significant differences between striped barrels and plain gray ones, even on hot days.<\/p>\n
An earlier broader comparison was conducted. In 2014, Caro and his team mapped striping across equid species and subspecies according to five potential pressures: camouflage, predator avoidance, heat regulation, social function, and annoyance from biting flies. Writing in Nature Communications, they observed consistent associations with one of these factors, specifically the flies.<\/p>\n
## What the flies actually object to<\/p>\n
So which part of the pattern do the flies genuinely dislike? In 2023, Caro and How returned to the paddock with 11 custom-printed patterns to determine: stripes of four contrast levels, plain grey, large black triangles, and small checks. Their research in the Journal of Experimental Biology revealed that plain grey coats attracted far more landings. Stripes with sharp contrast repelled flies, while those with faint contrast did not; the study found no evidence that polarized light, a longstanding hypothesis, had any impact.<\/p>\n
Horseflies are drawn to large dark shapes and struggle with significant dark shapes that are fragmented.<\/p>\n
## Cows in stripes<\/p>\n
Six Japanese Black cows, a breed distinguished by having only one color, took turns wearing painted-on zebra stripes. Tomoki Kojima at the Aichi Agricultural Research Center, together with colleagues from Kyoto University, rotated each animal through three scenarios: striped, only painted with black stripes, and left undisturbed. The middle scenario controlled for the paint itself, which is more significant than it seems. As reported in PLOS ONE, the striped cows attracted about half as many biting flies as the other two conditions, and exhibited noticeably less behavior such as twitching, stamping, and tail flicking. The researchers presented this as a method of pest control using no chemicals, substituting insecticide with a paint job.<\/p>\n
Each of these findings hinges on a single study, and relying on just one study is a precarious basis for a conclusion. The argument for biting flies holds validity because it does not solely depend on any single one of them: different teams, on various continents, working with diverse animals and testing distinct predictions, continually arrive at the same conclusion.<\/p>\n
None of this, however, renders stripes a complete barrier. Flies still discover the head, legs, ears, and every unpatterned area the stripes do not cover, and zebras continue to swish and twitch throughout the day. What stripes provide is a buffer, and against insects that carry trypanosomes and feed.<\/p>\n","protected":false},"excerpt":{"rendered":"
The equines in a paddock located in North Somerset were outfitted as zebras, causing the horseflies to struggle. That was the aim. Tim Caro, Martin How, and their team investigated tabanid horseflies at a livery yard in North Somerset, documenting their efforts to alight on captive plains zebras and standard domestic horses housed in the […]<\/p>\n","protected":false},"author":1,"featured_media":375482,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"Default","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[179],"class_list":["post-375481","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-source-scienceblog-com"],"_links":{"self":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/375481","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=375481"}],"version-history":[{"count":0,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/375481\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/media\/375482"}],"wp:attachment":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=375481"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=375481"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=375481"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}