The marmalade hoverfly (Episyrphus balteatus) is one of the most common and widespread hoverfly species found in Britain. Like many hoverflies, the males typically hover for long periods in a chosen sunspot, chasing away other males and intruders of all sorts (including butterflies), before returning to approximately the same position. In this case, the hoverflies were hovering about six or eight feet above a mostly shaded path (below) and occasionally landing on the large leaves for a few moments.
Some species of hoverfly defend three-dimensional territories; presumably in places where they are likely to encounter females. Some males hover at or near feeding and oviposition sites, while others actively search for females on flowers or near emergence sites.
Hoverflies usually congregate consistently at specific times and in specific locations, and many species exhibit some degree of territorial behaviour . They guard sunny spots, either by hovering in a shaft of sunshine (below) or by occupying a sunlit leaf, from which they dart up and out.
Hovering in a sunspot or shaft of light makes the fly very visible or apparent, and there is some evidence that these hover sites are leks; i.e. mating arenas without obvious resources where the males gather to display to females (below).
This territorial behaviour by hoverflies is widespread and common, but there appears to have been very little detailed research on the territoriality and lekking behaviour of different species. Definitely scope for research using the sort of photographic and or imaging equipment available to us today.