(A) Volume rendering of the dried heads of workers from the bee species used in this study. The right-hand side of a small B. terrestris head is shown (intertegular width (ITW) = 3.0 mm) in comparison to left hand side of a large individual from the same colony (ITW = 5.4 mm, note that the mandibles and some hair of this bee were too large to image). The ITW of the A. mellifera specimen was 3.6 mm. The box on the right displays a vertical section along the midline of a B. terrestris apposition compound eye showing the gross morphology of the lenses, crystalline cones (CC), and retina (indicated using colored outlines as in panel D). A portion of the optic lobe is also visible to the left of the retina. The lower box shows a transverse section across the ventral portion of the compound eye, showing the same features as in the vertical section. The approximate location of the sections are indicated with lines on the larger B. terrestris eye; both sections have the same scaling. (B) A volume rendering of the left compound eye (green) of each bee was aligned onto a rendering of the full head of another bee (grey), which allowed the segmented eye (cyan) to be placed relative to the head and also mirrored to the right side. (C) To measure the local facet dimensions, six points were selected on the opposing borders of the six facets that surrounded a central facet. These points were then used to compute the local structure of the facet lattice from which the lens diameter D was calculated (the horizontal (Dh) and vertical (Dv) facet dimensions were not used in this study). (D) Surface normal vectors (NV) were calculated from the exterior surface of the lenses to indicate the local viewing direction. The IF angle (ΔΦ) was defined as the difference between viewing directions at a distance of one lens diameter. The NV was traced into the eye and the points where it intersected the front surface of the CC, the retina, and the lamina interface were used to determine the thickness of these structures (Llens, Lcone, and Lretina, respectively). Note that the angle of the CC and the photoreceptors in the retina can be misaligned from the corneal NV, in which case the IF can differ from the IO angle. Inset, a diagram shows the measurement of ITW as the distance between the wing bases on a bee’s thorax. (Ei) The projection of the NVs (several are plotted as dotted lines) from the eye onto a sphere indicates the extent of the eye’s corneal projection (CP), which can also be represented on equirectangular (ii) or sinusoidal (iii) projections on which the CP is indicated by black lines. The color coding indicates the viewing direction, and was applied by stretching a 2D color map across the CP extent on the equirectangular projection in (ii); equivalent colors indicate the same viewing direction in each projection.