Telephlebia brevicauda

• Add to collection

A follow-up to previous sighting 4624247 to provide some detail. The first image shows a close-up of the dragonfly’s eye with a dark ‘pseudopupil.’ This feature, which can be seen in the compound eyes of dragonflies and other insects, provides the illusion of a real pupil that appears to move and follow the observer. The first image shows the compound eye is made up of multiple hexagonal shaped units called ommatidia. The pseudopupil occurs where the observer’s line of sight to the compound eye is looking directly down the depth of the ommatidia to the light-absorbing cells at their base. These appear dark as the incident light is absorbed by the cells. Moving out radially from the centre of the pseudopupil, the internal surfaces of the ommatidia are increasingly visible due to the curved outer surface of the eye and the reflected light from within the ommatidia. The pseudopupil becomes increasing lighter the further away the ommatidia are from the observer’s direct line of sight to the compound eye. As the observer moves around the compound eye, the individual ommatidia that are being viewed directly down to their light-absorbing cells will vary, giving the illusion that the pseudopupil moves around to follow the observer. The second image is a close-up of the dragonfly’s ocelli, the three small simple eyes that sit between the two much larger compound eyes. In this case the ocelli are on a raised mound between the two antennae and the larger simple eye towards the front has a white coloured butterfly scale draped across the top of it. The third image shows the pterostigma, a pigmented cell seen in the outer leading edge of the wings of dragonflies and some other insects. This thickened cell adds mass at a critical location of the wing and in doing so, enhances the dragonfly’s gliding and flight speeds by raising the critical speed at which self-exciting vibrations would occur in the wing, causing it to flutter.