J. Eur. Opt. Society-Rapid Publ. 22, 12( 2026) 115
Figure 1. Calliphora vicina( a – c) and Lucilia richardsi( d – f) blow flies displays vivid iridescent blue and green colours, respectively, on their abdomens and thoraxes. Optical microscopy( c, f) allowed to observe black hairs( i. e., macrotrichia) with lengths ranging between ca. 200 and 300 lm( c, f).
emerged C. vicina blow flies turns from grey to blue about two hours after emergence [ 9 ]. Such a process can be inhibited in some circumstances [ 9, 10 ]. The interference origin of this species colouration was revealed by immersion in chloroform, leading to a colour change to green [ 10 ]. More recently, the colouration variations of iridescent Lucilia sericata blow fly were investigated as a function of temperature( from ambient temperature up to 220 ° C) [ 11 ]. A periodic multilayer made of about 15 bilayers was observed in the cuticle of this insect. The bilayers were described by the superposition of a chitin layer the thickness of which was in the range 130 – 150 nm and a layer of air with a thickness ranging from 15 nm to 20 nm. Such multilayer epidermal structures in some species including wasps, flies, and beetles from the mid-Cretaceous have undergone a fossilisation process [ 12, 13 ]. In the case of an amber-entombed wasp species, Hou and coworkers demonstrated that the original structural colours were preserved through fossilisation. Unlike structural colours in dipteran cuticles, the optical properties of the eyes of many species( including Chrysomyia megacephala, Musca domestica and C. vicina) ranging from their colours to the sensitivities of their photoreceptors and autofluorescence were extensively investigated [ 14 – 24 ]. Blow flies such as C. vicina and L. richardsi have red eyes due to red-scattering screening pigments situated in their eyes’ pigment cells [ 19 ]. In addition to dipteran eyes’ optical properties, thin film interference was also found at the origin of the vivid iridescent colours of the wings of small Hymenoptera and Diptera [ 25, 26 ]. In Drosophila spp. and Chrysomya spp., the wing patterns were demonstrated to play a role in sexual selection [ 26 – 28 ]. For instance, in the case of Drosophila melanogaster, males with more vivid magenta wings are more attractive to females [ 27 ]. Similarly, it was demonstrated that Lispe cana male flies actively orient their iridescent sexual displays on their faces and wings toward the sun under full sunlight to enhance sexual signal visibility [ 29 ].
C. vicina and L. richardsi blow flies are necrophagous species. The former has been widely investigated in forensic sciences [ 30 – 32 ]. The post-feeding larval dispersal is an important element in the estimation of the post-mortem interval of human cadavers. Later on, L. richardsi was demonstrated to have a similar interest for forensic investigation [ 33 ]. These flies are indeed attracted not only by decaying flesh [ 34 ] but also by faeces [ 35 ]. In addition, they are known to be disease and infection vectors [ 36 ]. Due to its significant flight agility, C. vicina attracted attention from the research field of biomechanics. The neuromuscular control of steering forces on this insect during flight were investigated [ 37 ]. Within the insect’ s cuticle, mechanoreceptors, called campaniform sensilla and with the shape of elliptical holes, deform under strain [ 38, 39 ]. Through a bioinspiration approach, strain sensors embedded in space structures were developed [ 39 ].
In this research, using electron microscopy, different multilayers were found to be the mechanisms for the colour appearances of both investigated species. Photonic multilayers are widespread among natural photonic structures. They occur in the cuticles and wings of structurally coloured species of Hymenoptera [ 40 ], Lepidoptera [ 5 ] and Coleoptera [ 6, 41 – 44 ]. In addition to spectral measurements and optical simulations, we analysed the dipterans’ colours in terms of chromaticity as well as with respect to the visual sensitivities of the species and of some of their predators.