Bugs on the rooftop

Nut weevil (Curculio nucum)

As temperature increases we see a corresponding change in the insect community, specifically for the resource specialists -- the insects that feed on only one species of plant. Earlier studies have confirmed that specialist species also respond rapidly to destruction of their habitats, so we are dealing with a very sensitive group of animals.

A volunteer registration of insects for 18 consecutive years on the roof of the Natural History Museum of Denmark in Copenhagen has revealed local insect community turnover due to climate change. 1543 different species of moths and beetles and more than 250,000 individuals have been registered over 18 years of monitoring. That corresponds to 42 % of all the species of moths in Denmark and 12 % of the beetles. More interestingly, the insect community has changed significantly during that period.

The nut weevil (Curculio nucum) is an example of a resource specialist, feeding only on hazel. It lives further north in Europe than its close relative the acorn weevil (Curculio glandium), which feeds only on acorns. While the nut weevil was only registered during the first half of the study, the acorn weevil appeared in the last part of the study, suggesting that specialist species are moving northwards in Europe. Using the entire dataset, the study was able to confirm this trend and highlights the increased pressure on the most northern species, which may be 'squeezed out' of their range in the long term.

We are likely to lose some specialist species as they retreat north, but more new specialist species will arrive from the south. This trend is theoretically expected but extremely rare to confirm with observations across this many species. Insects are often over-looked and under prioritised for long term studies.

It was two employees of the Natural History Museum of Denmark with extensive entomological expertise who collected and identified all the insects. The monitoring took place every week from 1992 to 2009 through spring, summer and autumn using a light trap at the roof of the museum. What started out as a hobby based on scientific curiosity, ended up in an extensive faunal and climate change study.