Irish butterfly monitoring scheme detects decline above global average

The decline of butterflies and bumblebees in Ireland is matching a global trend, indicating insect populations are collapsing, according to the National Biodiversity Data Centre (NBDC).

Commenting on its latest figures, senior ecologist Dr Tomás Murray said Irish butterfly and bumblebee monitoring schemes have revealed rates of decline in these important insects in line with a worldwide study published earlier this week.

The global scientific review confirmed more than 40 per cent of insect species were declining and a third were endangered due to agricultural practices, urbanisation and climate change.

Asked if this threat of “catastrophic collapse of nature’s ecosystems” was being detected in Ireland, Dr Murray said: “Sadly yes, across the 120 sites in our butterfly monitoring scheme our recorders have detected an average annual decline of 2.6 per cent over the past 10 years, slightly above the global average of 1.8 per cent,” he added.

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Especially threatened

There were indications that bumblebees were especially threatened, as “across the 100 sites in the bumblebee scheme, our recorders have observed average declines of 3.7 per cent per annum over the past six years, markedly above the 1.0 per cent global average”.

“Whenever we release these figures we commonly get people responding saying ‘but there’s loads in my garden’, and that may be true for that lucky person in their one garden but across over 220 sites now walked for bumblebees and butterflies all over Ireland, this is certainly not the case,” he said.

Ireland has 14,500 species of insect, representing one-third of all species found on our landscapes and seascapes. However, to date only 1,051 (7 per cent) have had their conservation status assessed: 26 (2 per cent) species are now regionally extinct, 194 (19 per cent) are in decline of which 130 (13 per cent) are threatened.

Until the establishment of the NBDC in 2007, Ireland lacked any national systematic insect monitoring schemes and had no way of estimating long-term trends in its insect populations.

Dr Murray stressed the global study and Ireland’s national insect monitoring schemes were not being biased by rare and sensitive species. “What’s really frightening is that these trends largely reflect changes in our commoner species of insect as these form the bulk of insects detected by researchers and citizen scientists.”

Fixed route

The data is generated with the help of 180 citizen scientists monitoring 220 sites. Volunteers walk a fixed route – a 1 to 2km walk once a month from March to October for bees, or April to September for butterflies, and count the number and type of each insect they observe using a standardised methodology.

“When the numbers are compiled at the end of every season it’s humbling to see how much effort everyone is willing to give to support insect monitoring and conservation,” Dr Murray said.

Each year volunteers collectively walk on average of 3,740km over 2,040 hours, counting 51,100 insects across 48 species, “putting us streets ahead of many of our European neighbours in tracking change in these important animals”.

The network, however, needed to grow both in size, to successfully detect and monitor rarer species, and in scope so changes in other key insect groups such as predatory beetles and dragonflies could tracked too, he said.