Cover illustration: Be on the lookout . . .

One of the stalk eyed flies, Achias longividens (Walker), illustrated on the cover is found in South East Asia (this specimen is from Borneo) and shows a curious ocular adaptation with astonishing visual mechanisms and visual fields. The most instructive element of the biology of this animal, however, may be the understanding of its genetics. Its compound eyes are located at both ends of long stalks. These flies exhibit ocular sexual dimorphism which is not all that unusual in the dipterans as the males of many species have better acuity or different types of eyes from those of the females. Male ornaments that influence sexual selection are also not rare in the insect world, or even in the dipterans. But ornamented eyes are unusual. In at least eight acalyperate families, protuberences that are stretched out to form stalks can be found on the males and usually on the females of the same species. In most instances, the males have the longer “stalks” and sometimes spectacularly so. Investigators have described at least some male Crytodopsis whitei flies (another Borneo species) as having an 8 mm body length with eye stalks that have a combined span of 20 mm (Burkhardt D, et al, J Comp Physiol A 1994;1774:61–4). One wonders how such a creature would be airworthy.

These stalks are used by the males to help claim and retain territory. The males may engage in ritualised or even real fights in which there is simply a threat display or actual “jousting” with these stalks. Competitors are driven away by the more dominant male—usually the one …