Why don’t horseflies land on zebras?
Abstract: Stripes deter horseflies (tabanids) from landing on zebras and, while several mechanisms have been proposed, these hypotheses have yet to be tested satisfactorily. Here, we investigated three possible visual mechanisms that could impede successful tabanid landings (aliasing, contrast and polarization) but additionally explored pattern element size employing video footage of horseflies around differently patterned coats placed on domestic horses. We found that horseflies are averse to landing on highly but not on lightly contrasting stripes printed on horse coats. We could find no evidence for horseflies being attracted to coats that better reflected polarized light. Horseflies were somewhat less attracted to regular than to irregular check patterns, but this effect was not large enough to support the hypothesis of disrupting optic flow through aliasing. More likely it is due to attraction towards larger dark patches present in the irregular check patterns, an idea bolstered by comparing landings to the size of dark patterns present on the different coats. Our working hypothesis for the principal anti-parasite features of zebra pelage are that their stripes are sharply outlined and thin because these features specifically eliminate the occurrence of large monochrome dark patches that are highly attractive to horseflies at close distances.
© 2023. Published by The Company of Biologists Ltd.
Publication Date: 2023-02-17 PubMed ID: 36700395PubMed Central: PMC10088525DOI: 10.1242/jeb.244778Google Scholar: Lookup
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- Journal Article
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Summary
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This research seeks to understand why horseflies are deterred from landing on zebras. The study explores various visual mechanisms involving aliasing, contrast, polarization, and pattern element size. It finds that horseflies prefer not to land on highly contrasting zebra-like stripes and are somewhat less attracted to regular check patterns. It posits that the principal anti-parasite feature of zebra stripes is their sharply defined and thin parameters, which eliminate the occurrence of large dark patches attractive to horseflies.
Exploring Visual Mechanisms
- The researchers studied three potential visual deterrents for horseflies landing on zebras. These included aliasing, where the distinct bars of the zebra’s pattern might confuse or overwhelm the horsefly’s vision; contrast, where the stark black-and-white pattern of the zebra may seem unattractive or disorienting to horseflies; and polarization, where the manner in which the zebra’s coat reflects light might be off-putting to horseflies.
- The researchers also explored pattern element size as a deterrent by recording how horseflies interacted with differently patterned coats placed on domestic horses.
Results and Findings
- The study found that horseflies were hesitant to land on areas with high contrast, such as the stark black-and-white patterns similar to those found on a zebra.
- There was no evidence that horseflies were attracted or repelled by coats that reflected polarized light.
- Horseflies showed a slight aversion to landing on regular check patterns, but this effect was not big enough to support the aliasing hypothesis about the disruption of optic flow.
- It is suggested that this preference may be due to the attraction towards larger dark patches, which were present in irregular check patterns.
- The pattern size seemed to have an impact on horseflies’ attraction; they preferred landing spots with larger dark patches compared to smaller ones.
Conclusion and Hypothesis
- The researchers concluded that the key feature of zebra stripes that deters horseflies is the sharp, narrow boundaries of the stripes.
- This design eliminates large, single-color dark patches, which the study found to be highly attractive to horseflies.
- Hence, the thin and sharply defined stripes of zebras serve as an effective deterrent against horsefly landings.
Cite This Article
APA
Caro T, Fogg E, Stephens-Collins T, Santon M, How MJ.
(2023).
Why don’t horseflies land on zebras?
J Exp Biol, 226(4), jeb244778.
https://doi.org/10.1242/jeb.244778 Publication
Researcher Affiliations
- School of Biological Sciences, 24 Tyndall Avenue, University of Bristol, Bristol BS8 1TQ, UK.
- School of Biological Sciences, 24 Tyndall Avenue, University of Bristol, Bristol BS8 1TQ, UK.
- School of Biological Sciences, 24 Tyndall Avenue, University of Bristol, Bristol BS8 1TQ, UK.
- School of Biological Sciences, 24 Tyndall Avenue, University of Bristol, Bristol BS8 1TQ, UK.
- School of Biological Sciences, 24 Tyndall Avenue, University of Bristol, Bristol BS8 1TQ, UK.
MeSH Terms
- Horses
- Animals
- Equidae / parasitology
- Diptera
Conflict of Interest Statement
Competing interests The authors declare no competing or financial interests.
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