A chivalrous gentleman caller should always take a gift along when visiting a lady, and this often holds true in the animal kingdom. Such items are usually nutritional - perhaps wine, chocolates, a fly snatched from a spider’s web, a gelatinous substance synthesised internally beforehand - and often advertised by the male during the courtship phase. Females may then be able to assess the quality of these ‘nuptial gifts’, and shun those males who have been so rude as to turn up empty-handed.
In empidid flies, such as the dance fly Empis opaca pictured above, males usually fly in a swarm at a landmark site, holding captured prey beneath them. Females can compare the gifts available, select a male, then take the offering in order to assess it properly before deciding whether to accept him as a partner. Not only has the gift shown here secured this male a mating, but it also means that she has extra nutrition which can be used to furnish her eggs.
The world of nuptial gifts and courtship feeding in invertebrates is wide-ranging, species-specific, and often quite bizarre, so we shall be coming back to them again in future. How bizarre, you ask? Well, in the particular species pictured here, males often have success with females after having carefully prepared a balloon of willow-seed fluff, which they offer up instead of a dead fly. Perhaps this shows that they are sensitive, arty souls? More likely that they are taking advantage of a sensory bias with little adaptive value, but we all get fooled sometimes…
For further reading on this topic, I recommend Karim Vahed’s excellent 2007 Ethology review ‘All that glisters is not gold: sensory bias, sexual conflict and nuptial feeding in insects and spiders’.
Original photograph taken from http://www.wildaboutbritain.co.uk/archive/showphoto.php/photo/94766