J. Eur. Opt. Society-Rapid Publ. 2026, 22, 12 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2025053 Available online at: https:// jeos. edpsciences. org
Journal of the European Optical Society-Rapid Publications
RESEARCH ARTICLE
Structural colour and photonic mechanisms in the blow flies Calliphora vicina and Lucilia richardsi( Diptera: Calliphoridae)
Élise Camus 1, 2, Ewan D. Finlayson 3, Pete Vukusic 3, Olivier Deparis 1, and Sébastien R. Mouchet 1, 3, 4, 5,*
1 Department of Physics & Namur Institute of Structured Matter( NISM), University of Namur( UNamur), Rue de Bruxelles 61, 5000 Namur, Belgium 2 Département de Physique, École Normale Supérieure de Lyon / Université Claude Bernard Lyon 1, 46 Allée d’ Italie,
69364 Lyon Cedex 07, France 3 Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, United Kingdom 4 Institute of Life, Earth and Environment( ILEE), University of Namur( UNamur), Rue de Bruxelles 61, 5000 Namur, Belgium 5 Micro- and Nanophotonic Materials Group & Research Institute for Materials Science and Engineering, University of Mons,
Place du Parc 20, 7000 Mons, Belgium
Received 23 September 2025 / Accepted 3 December 2025
Abstract. Structural colours in natural organisms are created by complex photonic architectures giving rise to remarkable visual appearances. In arthropods, these structures are usually made of biopolymers and comprise photonic crystals. They are often iridescent, i. e., their colours depend on the incidence and observation angles. Despite the interest of the scientific community in a large variety of species including those belonging to butterflies and beetles, some orders such as dipterans have been overlooked so far. In this work, the structural colours from the abdomens of two dipteran species, namely Calliphora vicina and Lucilia richardsi blow flies, with different displayed colours were investigated by spectrophotometry and optical simulations. Using electron microscopy, we identified multilayer photonic structures as the primary mechanism responsible for their visual appearances, with possible additional thin-film interference in C. vicina. In addition, the dipterans’ colours were analysed in terms of chromaticity as well as with respect to the visual sensitivities of the species and the ones of some of their predators. The reflectance spectra of the blow flies investigated were found to correlate with high absorption by their own and their predators’ photoreceptors. These findings indicate that structural colouration in blow flies may influence not only communication with conspecifics but also interactions with predators.
Keywords: Structural colour, Natural photonic crystal, Photonic bandgap materials, Bragg mirror, Diptera, Blow fly.
1 Introduction
Structurally coloured living organisms exhibit complex optical structures leading to striking visual appearances [ 1 – 4 ]. In insects, these structures are often photonic crystals made of biopolymers such as chitin. A signature of the interference origin of such structural colours is iridescence, i. e., the displayed colours depend on the incidence and viewing angles. Many species have attracted much attention from the natural photonics scientific community since the 19th century such as butterfly species from the family Nymphalidae( e. g., Morpho genus), the family Papilionidae( e. g., Papilio genus) and the family Lycaenidae( e. g., Polyommatus genus) [ 1, 5 ] or beetle species from the family Buprestidae( e. g., Chrysochroa genus) and the family Scarabaeidae( e. g., Chrysina genus) [ 6 ]. However, species from some
* Corresponding author: sebastien. mouchet @ umons. ac. be orders such as Diptera have been far from extensively investigated. In this work, we analysed the structural colours from the abdomens of different but related dipteran species from the family Calliphoridae, namely Calliphora vicina( Robineau-Desvoidy 1830, formerly known as Calliphora erythrocephala) and Lucilia richardsi( Collin 1926), each displaying various structural colours( Fig. 1). Most species in the order Diptera are known to exhibit colours from pigment origin. For instance, black visual appearances are associated with melanin [ 7 ]. Green colourations of adult specimens of some species from the family Chironomidae originate from bilin pigments [ 7 ]. These pigments are metabolic products of porphyrin compounds found in the haemoglobin at the origin of red colours in the larvae of the related species [ 7 ]. However, already in 1927, Mason described the colour of Lucilia sp.“ and other“ blue bottle” flies” as“ metallic iridescent” due to a relatively thin colour-producing layer [ 8 ]. In 1935, Fraenkel described that the cuticle of newly
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