March Brown Mayfly

The March Brown is probably the most famous of all British mayflies. It is sacred to anglers across the UK and has been copied by them to help catch fish for over 500 years. Originally the March Brown Mayfly was confused with the False (or Late) March Brown (Ecdyonurus venosus). But, in 1931, the March Brown Mayfly (Rhithrogena germanica) was officially recorded in Britain.

Fast Facts

Latin name: Rhithrogena germanica

Where in the UK: River Tweed and River Don in Scotland, the River Wye in Wales, the River Liffey in Ireland and the River Coquet in England

March Brown Mayfly

Where is it found?

It is found in large, clean rivers such as the River Tweed and River Don in Scotland, the River Wye in Wales, the River Liffey in Ireland and the River Coquet in England.

Early to emerge

The March Brown is quite extraordinary for a mayfly. Most mayflies like to emerge as adults during the warm summer months, however, the March Brown emerges right at the end of the winter – from March to early April. Adults emerge from the river around about midday. The larvae drift in the water and then emerge at the surface. As they are emerging they are an easy target for fish and birds so they emerge very quickly – often taking less than 30 seconds to moult and fly off the water!

Two adult life stages

Mayflies are unique as insects in having two adult stages. The adult that emerges from the water is called a subimago or ‘dun’. Usually this stage is relatively short, with the subimago resting on bankside vegetation before moulting its skin again and becoming an imago or ‘spinner’. The March Brown however has the longest subimago stage of any mayfly. After they leave the water’s surface they immediately fly to the bank and land on the ground they then fly up to a nearby tree. They’ll then rest in the leaves of the tree for anything up to four days before moulting.

Why does this mayfly need our help?

Numbers of this species are in decline across Europe. Whilst the March Brown can tolerate some pollution it relies on lots of oxygen in the water. As a result it favours faster flowing stretches of water. It’s thought that because this species has to grow rapidly during the winter that it might be more prone to disturbance due to natural or artificial changes to the conditions in the river during this period.

What is Buglife doing to help?

Buglife is currently working in collaboration with the Riverfly Partnership on the conservation of riverflies in the UK.