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Sunday 21st December, 2014

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Netted Carpet Moth Survey 2010

Looking at the tall-standing bundle of bright-green plants in front of me, I’m thinking “Will I be able to find one of these caterpillars?”.
This mammoth task should not be under-estimated, there are around 200 plants and the moth caterpillars, which we are surveying for, are tiny and well-camouflaged, closely resembling the seed pod of this plant.

The caterpillars I refer to are of the Netted Carpet moth, which is reliant on the food plant ‘Touch-me-not balsam’. The Netted Carpet moth Eustroma reticulatum is recorded in the Red Data Book as Vulnerable, with the Touch-me-not balsam being ‘Nationally Scarce’.

Netted Carpet moth - Eustroma reticulatum
Netted Carpet moth © Graham Jones

When I saw my first Netted Carpet Moth caterpillar it was a relief, and as the day went on, it became usual procedure to move to different patches of plants counting the caterpillars. One individual would shout “I’ve got 3 on this plant”, whilst another said, “I’ve only got one!”. It was a great team building exercise, whilst at the same time, gathering important data about rare species.

The methodology is simple, once you have estimated the number of plants by looking at the stems; you then check every plant, looking underneath the leaves for the larvae. By the end of the day, the bottom of your spine is well and truly aching.

Up-close of the Touch-me-not Balsam
Up-close of the Touch-me-not Balsam plant © Graham Jones

Touch-me-not balsam (also known as Yellow Balsam), Impatiens noli-tangere, is a rare plant and the only native balsam in Britain. Easily distinguished from other balsams by its large yellow flowers, its distribution is extremely restricted. Indeed in England there are only 8 recorded sites, all found in the Lake District and here at Muncaster we are fortunate enough to be one of those eight.

Young stems of Touch-me-not balsam in hoof prints
Young stems of Touch-me-not balsam in hoof prints © Graham Jones

The plant prefers to grow on nutrient-rich soils (usually in damp semi-shaded woodlands). It is a ruderal species, meaning it can quickly colonise newly disturbed ground, but is intolerant of competition with perennial vegetation (i.e. Common Nettle Urtica diocia, or Creeping Buttercup Ranunculus repens). The key to its success is to regularly disturb the ground during winter months (historically done by cattle grazing). At the Muncaster site, the ground is disturbed by man-power alone. The ripe seeds of the Touch-me-not balsam can ‘ping’ up to 2 metres away from the plant, where it is raked or trodden into the earth by staff and volunteers.

An area of around 1000 plants is needed for the Netted Carpet moth to survive and they can fly over a quarter of a mile, attracted to the scent of the Touch-me-not Balsam flower. This moth usually lays its eggs on the food plant in straight lines, following clear flight paths between July and August, and it is estimated that only half will hatch to become caterpillars.

Each year, Butterfly Conservation, survey for and report on numbers of moth larvae and plants. With the earliest record of Netted Carpet Moth at Muncaster occurring in 1990’s, numbers have steadily risen each year with 9 recorded larvae on 630 plants in 1998, up to 218 recorded larvae on over 3,000 plants in 2007.

Muncaster Survey Muncaster Survey © Andy Long


An example of NC caterpillar forming a triangle shape
An example of NC caterpillar forming a triangle shape © Graham Jones

The video shows the team here at Muncaster doing the survey. There are a couple of shots where the caterpillar is not clear, but it gives you an idea of how well they blend in. With practice, you do get better at spotting them. I gained confidence when I learnt that one of the tricks is to kneel down and see them from under the canopy, where the caterpillars can form a triangle shape by sitting connected to both the leaf and the stem.

In this year’s survey a total of 269 larvae were counted at Muncaster – which is a great result and shows a positive increase of both the plant and moth species. An important conservation success considering both the plant and caterpillars are elusive and extinct in other regions of the country.
Here at Muncaster the World Owl Trust will continue to aid the dispersal and survival of both the Touch-me-not balsam and the Netted Carpet moth.

For any more information please read the factsheet from Butterfly Conservation, found here:

With thanks to the following people who took part in the Muncaster survey:

  • Dr. Paul Hatcher (University of Reading)
  • John Hooson (National Trust)
  • Sue Hazelwood (volunteer)
  • David Armitage (Collections Manager)
  • Hilary Lange (UK Conservation Officer)
  • Rebecca Kiggins (Ass. Conservation Officer)
  • Andy Long (volunteer)
Rebecca Kiggins
October 2010
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