Its insect week!

21st Jun 2023
by Jamie Ribbens

Riparian zones bridge the gap between land and river, creating an important habitat for insects while also providing shade and protection against erosion. We do a lot of habitat work mainly to help aquatic species like fish, but we are keen to monitor and understand the wider biodiversity benefits.

Some moths from the moth trap
Some moths from the moth trap

It is Insect Week so this news item is very relevant now! Due to a moth’s sensitivity to environmental changes, looking into their diversity and abundance can indicate how good a habitat is for supporting specialist species that rely on certain trees and food plants.  In order to further understand this, GFT set up a moth trap to look at moth diversity and abundance between different sites.  Over the course of three days a 6W 12V Portable Heath Moth Trap was set up with a battery along the Grange Burn.  It was turned on at 10.30pm and collected at 7.30am the following morning.  The moth trap contained egg boxes and cardboard with nooks to offer moths a place to hide. 

Heath traps do not retain the full catch but have a good hold rate.  Each moth was identified and released in a shady, overgrown spot to protect from predation, away from the catch site to avoid recapture.  Trapping season tends to be March through until October and last week offered optimal conditions with warm nights, cloudy and still.  Trapping during wind, rain and clear skies can affect catches.

The first site was a riparian area that had trees planted 20+ years ago as part of a GFT habitat restoration project, the second site had recently been fenced off and planted with trees in 2021.  The final site was placed by the burn where it has been fenced off and the burn is surrounded by gorse and then rough grazing.  It was interesting to find similar moth species between the two planted sites with more abundance at the older tree site.  The last site had the most species but lower in abundance than the first site.  The moths found at the first two sites were typical woodland moths such as the Poplar hawk moth.  One of the most abundant moths caught was the Heart and dart which is supposedly most abundant in arable grassland and pasture but was recorded most in the first site.  At the final site a cinnabar was found which is to be expected as they thrive in open grassy land. White ermine and Buff ermine were found at all three sites which again makes sense as they are found in most habitats.  The first site was host to a Buff tip moth which as a caterpillar feed on deciduous trees so it would be interesting to go to that site in July and look for caterpillars because while moths can fly it would be interesting to see what generations each habitat can support.  Comparing the data from site one and two shows there is a clear biodiversity benefit where more mature riparian trees are found!  It would be interesting to see in 20 years if site two produces the similar abundance to site one.

The data is presently being written up and the final report will be available soon.  

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