Sub-micromorphology of the epicuticle of hornets: AFM studies

The upper part of the hornet cuticle in the abdominal region reveals several structures. First, situated at intervals of 10 microm or more apart, there are depressions housing a peripheral photoreceptor (PP) and between every two of these, there are horizontal flats resembling an irregular polygon which are mostly elongated and about 100 microm2 in area. Upon each such terrace-like flat there are tile-shaped protuberances up to several micrometres in length and mostly running parallel to one another, covering the entire surface. Between every two such terraces there is a 'step' of up to 1.4 microm in height. Both the 'tiles' and 'steps' terminate in front of the distal part of each PP, which is a recessed and smooth region. Secondly, in other regions of the cuticle one can note other surface configurations such as: (a) a paucity of 'tiles'; (b) no 'tiles' at all but a chessboard-like pattern, the 'squares' of which contain rectangles recessed to various depths, interspersed among 'plaques' that are not recessed and may even protrude; and (c) anfractuous (characterized by windings and turnings) flats that are intermittently criss-crossed by grooves. In addition to the above, most of the cuticle also displays numerous setae (i.e. small hairs). We suppose that all the described structures and configurations either contribute to enlargement of the cuticular surface, or act as an optical grid, thereby enhancing the absorption of light. We further speculate that for hornets in flight, situations may arise where part of the above mentioned structures orientates perpendicular to the sunlight and this entire orientation acts to direct the solar energy toward and into the PP so as to enable greater utilization of light as an energy source.