The pandemic year of 2020 provided a unique opportunity to observe the behavioural strategies of two species of Eristalis.

Although constrained by the pandemic to spend a lot of time at home,  the unusually fine weather brought insect ecology to my garden, and the great reduction in car traffic on the roads allowed visits from many more insect species.

From mid-March to May I had daily visits from Eristalis pertinax, mostly males which chose an open part of the garden for hovering, and on some days hovering continued for several hours into the afternoon.

From May through till Autumn, the most regular hoverfly was E. tenax, males of which often appeared early in the morning, as soon as the flower beds received direct sunshine. In this species, mate searching behaviour was mostly seen early in the day, presumably because there was a need to find recently emerged and unmated females. 

Males of E. pertinax appeared later in the day. Many hours of observation showed no sign of "territorial" behaviour. The hovering is not at one fixed point in space, but the males would drift, turn, dart and switch positions every few seconds.

Although Eristalis normally fly quietly, a slow buzzing flight is used by female E. pertinax around possible sites for oviposition, and by female E. tenax flying indoors when hibernation sites are needed.

It was my good fortune that some female E. pertinax chose to scatter eggs around the top of a kitchen drain, from which a small brood was reared.