Structural colour and photonic mechanisms in the blow flies Calliphora vicina and Lucilia richardsi (Diptera: Calliphoridae) | Journal of the European Optical Society-Rapid Publications

Open Access

This article has an erratum: [https://doi.org/10.1051/jeos/2026021]

Issue		J. Eur. Opt. Society-Rapid Publ. Volume 22, Number 1, 2026


Article Number		12
Number of page(s)		12
DOI		https://doi.org/10.1051/jeos/2025053
Published online		24 February 2026

Supplementary Material

Supplementary material 1

Figure S1.

Top view of the cuticle of Calliphora vicina’s abdomen using SEM. In addition to long hairs (known as macrotrichia) observed by optical microscopy, shorter hairs (also called microtrichia) of about 20 μm can be observed.

Supplementary material 2Co- and cross-circularly polarised reflectance spectrophotometry.The dipteran cuticles were characterised using cross- and co-circularly polarised (CP) reflectance spectrophotometry. Both co-CP and cross-CP configurations were investigated, where co-CP corresponds to incident and reflected CP components with the same handedness (left (L) or right (R)) and cross-CP refers to different handedness of the incident and reflected CP components. The experimental set-up, detailed in [65], consisted of an Ocean Optics (Delray Beach, FL, USA) USB2000+ spectrometer and an Ocean Optics HPX-2000 xenon broadband fibre-coupled light source. CP incident light beam was generated by a rotatable polariser and an achromatic Fresnel rhomb quarter-wave retarder, orientated at 45° azimuth. The CP light handedness was selected by orientating the polariser azimuth at either 0° or 90°. The incident light was focused onto a piece of Diptera cuticle at normal incidence using an achromatic × 10 objective lens, leading to a beam spot diameter of ca. 30 μm. This lens collected light backscattered by the sample, which was conducted by a beam-splitter through a CP analyser comprising the Fresnel rhomb and a second rotatable polariser. A plane aluminium mirror was used for the measurement calibration.Supplementary material 3

Figure S2.

CP reflectance spectrophotometry was used in order to highlight possible light-polarising effects arising from the pattern observed within Calliphora vicina’s cuticle that might be associated with a Bouligand structure. Despite the electron micrograph observations, only cross-CP components have significant intensities. Co-CP reflectance spectra that usually contains the signature of Bouligand structures display negligible intensities.

Supplementary material 4

Figure S3.

Reflectance spectra of a pseudo-periodic multilayer derived from Calliphora vicina photonic model (Fig. 7) with random thickness deviations of ± 15 nm in the high-contrast layers and ± 5 nm in the low-contrast layers. The resulting calculated spectra were averaged over incidence angles from −5° to +5°. A broader reflectance peak than the ideal model (Fig. 8a) is observed, though still narrower than the measured spectrum (Fig. 3a).

Supplementary material 5CP reflectance was modelled for various incidence angles using a one-dimensional 4 × 4 matrix method for anisotropic multilayers [83]. The model comprises a Bouligand structure overlaid by an interferential thin film. The Bouligand structure contained 18 half-pitches of 118 nm, had an average refractive index of 1.56 [79], and exhibited an in-plane birefringence of 0.018 [66]. The overlying thin film was modelled as a 180-nm thick isotropic layer with a refractive index of 1.75. All materials were assumed to be non-absorbing.Supplementary material 6

Figure S4.

For comparison, CP reflectance was modelled for a Bouligand structure (18 half-pitches of 118 nm, an average refractive index of 1.56 [79], in-plane birefringence of 0.018 [66]) covered by a 180 nm-thick isotropic film (n = 1.75), calculated for incidence and emergence angles ranging from 0° to 75° in 15° increments in cross-CP configuration (a) and at normal incidence in co- and cross-CP configuration (b). Modelled CP reflectance spectra in (a) appear as broad as the experimental spectra measure from Calliphora vicina (Fig. 3a). The left-left co-CP (LCP-LCP) spectrum exhibits a small peak in the UV range. In the real photonic structure of C. vicina, positional disorder [44], light absorption, and scattering would likely reduce this co-CP signal to a very weak level.

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