Taking to the Air

David Attenborough © BBC

Most insects possess the ability to fly, or have done at some point in their evolutionary history. The evolution of flight is thought to be one of the factors that has lead to the tremendous diversity of insects.

Life in the Undergrowth programme 2 Taking to the Air focuses on flight and introduces some of the amazing insects that use their flying ability to perform incredible feats. In this programme David Attenborough comes face to face with the largest insect on earth – the mighty Titan beetle!

Dragonfly (Cordulegaster bidentata) © Dragiša Savic

Riverflies

David Attenborough © BBC

If you were to take a walk by a river or lake on a warm summer’s evening you are likely to encounter clouds of riverflies. That is, of course, if that particular river or lake is healthy and free of pollutants. Riverflies are a beacon for the health of our rivers, lakes and other freshwater habitats. These insects are the very lifeblood of our rivers and lakes. They provide food for fish, birds and bats. Without riverflies the fish pursued by anglers and animals such as the otter, kingfisher and heron would go hungry.

Riverflies include mayflies, caddisflies and stoneflies.

STAR FILE: Mayflies

Mayfly (Ephemera vulgata) © Jon Mold

Mayflies are also known as upwing flies, on account of them holding their wings in an upright manner when at rest. Although commonly called mayflies this name is somewhat misleading as they can appear throughout the year. The name mayfly comes from the habit of one species Ephemera dancia which emerge from the water as adults when the Mayflower or Hawthorn is in bloom. In the past they have also been known as ‘dayflies’, as some species have an adult life lasting just one day.

Invertebrates in Danger! Riverflies

Riverflies are a good indicator of the health of rivers and streams, this is because they are very sensitive to changes in the quality of the water that they live in. Unfortunately where the water has become polluted, or where the amount of water flowing through rivers and streams has decreased through increased domestic and agricultural use by humans. There is strong evidence that over at least the last 15 years there has been a widespread decline in the abundance of a number of species of riverfly in the UK. For instance, the Iron Blue mayfly has declined by as much as 80% in recent decades.

Buglife are playing an important role in the Riverfly Interest Group, to identify the causes of riverfly declines and to take appropriate action to halt this grave situation.

Another way in which Buglife are working to halt the decline in our riverflies is through putting pressure on the government to ban Pyrethrin-based sheep dips. Sheep farmers dip their stock in sheep dip to protect them from external parasites. However, the chemicals that are used are indiscriminate and incredibly toxic to wildlife. Where these chemicals are accidentally released into rivers and stream the impact can be devastating. Even a tiny amount of the chemical dripping from a wet sheep into a stream will kill all the invertebrates for up to 10 kilometres downstream, with knock-on impacts for fish, the rest of the aquatic ecosystem and fishing businesses.

For more information on the Riverflies Project click here.

Flies

St Mark’s Fly (Bibio marci) © Dragiša Savic

Flies are all members of a group of insects called the Diptera (from the Greek words di = two, and pteron = wing). Flies have two large fore (front) wings which provide the power for flight. The second pair of hind wings have been reduced to tiny club-like structures called haltares. The fly uses these haltares as gyroscopic balancing devices during flight to help it change direction.

There are at least 6900 species of fly in the UK, and these are split into two groups: the threadhorns and the shorthorns. The scientific term for the threadhorns is the Nematocera, this group includes more primitive flies such as craneflies, gnats, midges and mosquitoes. The shorthorns (also known as the Brachycera) represent all the other flies, including the various species that we think of as typical flies such as hoverflies, houseflies and bluebottles.

Flies are friends
Flies receive a lot of bad press, if you were asked to name your favourite insect a fly might not immediately spring to mind! However, flies are incredibly important, and there are actually very few British species that are pests or cause a nuisance. Flies play an essential role in the decay and decomposition of organic material and wastes, they also therefore are of vital importance to the recycling of nutrients. The adults of many species visit flowers and are important pollinators of our crops and wild flowers. The larvae of some hoverflies are also friends to the gardener, eating aphids such as greenfly which would otherwise damage crops.

A long-legged fly (Dolichopus sp.) © Ben Hamers

Amazing!
Flies have played a crucial role in our understanding of genetics and evolution. Did you know that much of our understanding of DNA has come from research into a fruit fly?

FACT FILE: Hoverflies

A hoverfly (Chrysotoxum bicinctum) © Nigel Jones

Hoverflies are masters of disguise, many have black and yellow stripes to mimic wasps and bees, there are even furry bumblebee mimics. If you see a wasp or bee hovering, or investigating dead wood, take a closer look because you may be watching a fly! The hovering of male hoverflies is an incredible feat; they can often hang in the air for many hours during sunny weather. This behaviour would seem to be a strategy for attracting female hoverflies to mate. The males hold small three dimensional territories within loose swarms and only interrupt their hovering to chase off a rival, or to intercept a female. Try catching one and you will find that they have exceptional reactions!

Some hoverfly species are able to migrate for hundreds of miles from continental Europe to the UK, some reaching areas as far north as the Hebrides and the Western Isles. Some summers many of the hoverflies you see in your garden will be immigrants. This is an astonishing feat for such small and delicate creatures.

Two male hoverflies (Eristalis arbustorum) attempt to attract a female’s attention by hovering overhead © Nigel Jones

Invertebrates in Danger! Golden Hoverfly
The Golden Hoverfly (Callicera spinolae) is a large, colourful, hairy hoverfly that is in trouble. It is found in East Anglia, and has only historically been known from eight sites. Recent surveys for the hoverfly have only found it at two sites, if it is lost from these sites it could become extinct in the UK.

Where present the adults can be found feeding from ivy flowers in autumn. The larvae live in rot holes in trees. Golden hoverflies are saproxylic, they are dependent on decaying wood.

A possible reason for the decline of this species is a lack of rot holes in trees. Changes in woodland management have lead to a decline in available dead wood in UK woodlands. Where the amount of dead wood, either as fallen branches and trees, or as decaying parts of live trees, has declined so has the invertebrate fauna reliant on this habitat. There are more than 1700 different invertebrate species in Britain and Ireland which are dependent on decaying wood in order to complete their life cycles. These include other hoverflies, longhorn beetles, bark beetles, and some click beetles. These species are suffering a similar fate to the Golden hoverfly.

Golden hoverfly (Callicera spinolae) © Rob Garrod