Dragonflies face uncertain future

12:09 GMT, Friday, 15 May 2009 13:09 UK

Matt Walker
Editor, Earth NewsAt least one in ten species of dragonfly and damselfly are threatened with extinction, according to the first world survey of their numbers.

The figure may be an underestimate as so little is known about many species.

However, the news is not all bad. The survey published in Biological Conservation is the first to assess the vulnerability of any insect group on a global scale.

And it suggests the extinction risk faced by insects has been exaggerated.

Viola Clausnitzer led an international team of conservation scientists from Germany, Australia, Japan, Russia and the UK among others. They reviewed the status of a random sample of 1500 of the 5680 dragonflies and damselflies known to science.

The team assessed the population and distribution of each species according to the Red List criteria set down by the World Conservation Union (IUCN).

They found that more than half of the species should be categorised as Least Concern, which means they likely remain widespread globally, or are not threatened even if they live in a restricted range.

But one in 10 species is threatened, meaning it is categorised as critically endangered, endangered or vulnerable.

"It's fair to say that is an underestimate," says Clausnitzer, as too little data exists to accurately assess the status of 35 per cent of the species.

Dragonflies and damselflies, which belong to the insect order known as the Odonata, are susceptible because the larvae of each species live in water. So pollution and changes to habitat, such as forest degradation, which affect water courses can have an impact.

Indeed, because of their sensitivity to water and habitat quality, dragonflies are frequently used to assess environmental health. With their striking colours and behaviour they can be used as indicator species. "If they disappear you've got something wrong with your habitat," says Clausnitzer.

Those species most at risk tend to live in south east Asia and Australia.

In south east Asia, a large number of species are endemic to islands such as the Philippines or within Indonesia, and cannot escape detrimental impacts on their habitat.

In Australia, climate change is having an especially strong impact on freshwater systems.

The survey is the first to assess the global health of any order of insects. Compared to vertebrates, the dragonflies and damselflies are not doing badly.

"Amphibians are more threatened than dragonflies in general," says Clausnitzer. Amphibians are being particularly afflicted by the deadly chytrid fungus. "Another difference is that adult dragonflies are more mobile. If one site is destroyed they still have the chance to fly to another site, which frogs don't have."

They also seem less to be less threatened than the mammals, but at a similar level of risk as birds.

"We were a bit surprised that the dragonflies are not that bad off," says Clausnitzer.

"There is a big discussion going on about invertebrates and extinction rates in insects, and this discussion is not based on any real figures. It is all estimations," she adds.

In general, conservationists have feared that a much higher proportion of insect species face extinction.

However, Clausnitzer cautions that much more research needs to be done to be sure, and different groups of insects might face very different challenges.

For instance, while the reliance of dragonflies and damselflies on water makes them susceptible, says Clausnitzer "dragonflies are the strongest fliers in the insect kingdom. So you might get a very different picture if you take less capable fliers."

http://news.bbc.co.uk/earth/hi/earth_news/newsid_8040000/8040926.stm