Colour patterns often influence how animals interact with one another, but the ability of researchers to quantify pattern per se is hampered by a lack of easily accessible and user‐friendly measurement software packages. We address this issue by releasing pat‐geom, a free software package for use within ImageJ that allows users to measure seven properties of a pattern: (a) the shape of its markings, (b) the directionality in the shape of its markings, (c) the size of its markings, (d) the contrast of the pattern, (e) the distribution of its markings, (f) the directionality in the distribution of its markings, and (g) the randomness of the pattern. We provide examples of how pat‐geom may be used, such as to visualise the “average pattern” of a population of animals, or to compare the patterns on two animals. Using data from two case studies, we also demonstrate pat‐geom's ability to identify the specific aspects of an organism's pattern that match its background and to design artificial prey items that accurately resemble their model organism for use in predation experiments. pat‐geom collates the tools to measure these seven diverse properties of animal colour patterns into one convenient, easy‐to‐use package. It can be employed in a wide range of studies on topics such as aposematism, camouflage and mimicry, and also has the potential to be applied to other research fields such as landscape ecology, botany and cellular biology.

There are fewer eyespots on the forewings versus hindwings of nymphalids but the reasons for this uneven distribution remain unclear. One possibility is that, in many butterflies, the hindwing covers part of the ventral forewing at rest and there are fewer forewing sectors to display eyespots (covered eyespots are not continuously visible and are less likely to be under positive selection). A second explanation is that having fewer forewing eyespots confers a selective advantage against predators. We analysed wing overlap at rest in 275 nymphalid species with eyespots and found that many have exposed forewing sectors without eyespots: i.e. wing overlap does not constrain the forewing from having the same number or more eyespots than the hindwing. We performed two predation experiments with mantids to compare the relative fitness of and attack damage patterns on two forms of Bicyclus anynana butterflies, both with seven hindwing eyespots, but with two (in wild-type) or four (in Spotty) ventral forewing eyespots. Spotty experienced more intense predation on the forewings, were shorter-lived and laid fewer eggs. These results suggest that predation pressure limits forewing eyespot number in B. anynana . This may occur if attacks on forewing eyespots have more detrimental consequences for flight than attacks on hindwing eyespots.

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Small marginal eyespots on lepidopteran wings are conspicuous elements that attract a predator’s attention to deflect attacks away from the body, but the role of ultraviolet (UV) reflectivity at the center of these patterns and variation in eyespot number in altering the function of eyespots remains unclear. Here, we performed a field-based predation experiment with artificial prey items based on the appearance of squinting bush brown butterflies Bicyclus anynana (Butler, 1879). We tested how two visual properties of the wing pattern affect predation risk: i) the number of eyespots on the ventral forewing surface—two or four; and ii) the UV reflectivity of eyespot centers—normal (where the UV reflectivity of the centers contrasts strongly with that of the darker surrounding ring) or blocked (where this contrast is reduced). In total, 807 prey items were deployed at two sites. We found a significant interaction between the number of ventral forewing eyespots and UV reflectivity in the eyespot centers: in items with fewer eyespots, blocking UV resulted in increased predation risk whereas in items with more eyespots, blocking UV resulted in decreased predation risk. If higher predation of paper models can be equated with higher levels of wing margin/eyespot conspicuity, these results demonstrate that UV reflectivity is an important factor in making eyespots more conspicuous to predators and suggest that the fitness of particular butterfly eyespot number variants may depend on the presence or absence of UV in their centers and on the ability of local predator guilds to detect UV.

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