Caddisflies' summer spectacle in Dover city centre
1 August 2013 Last updated at 12:24 BST
Richard Taylor-Jones witnesses the caddisflies' summer mating spectacle on the River Dour in Dover city centre.
Tens of thousands of flies take off from the river with the sole purpose of mating as quickly as possible.
The flies in their adult phase may only be alive for a few hours, but the ensuing spectacle of them flying up and down to attract a mate is a thrilling visual experience.
It is even more remarkable for taking place in the heart of a busy city centre.
Urban Jungle is broadcast on Thursday, 1 August at 19:00 BST on BBC One South East and nationwide on the iPlayer for seven days thereafter.