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THE RARE NETTED CARPET MOTH

 Netted Carpet moth

The Netted Carpet moth is one of Britain's most endangered moths and the Lake District is its only stronghold. It was heavily collected by the Victorians and thought to be extinct early in the 1900's. It was rediscovered in 1945. Twenty years ago the species was known from about 25 locations in the area, but current estimates suggest that up to half of these sites no longer support the moth.

The larvae of the moth feed exclusively on touch-me-not Impatiens noli-tangere which is itself a scarce plant in Britain, also with a Lake District stronghold. The plant grows in damp woodland, usually besides streams where nutrient rich silt has accumulated, by wet roadsides and timber extraction sites. At present just eight sites are known to hold the moth; the main colonies occur in the area between Coniston Water, Lake Windermere and the Rusland Valley....with an outlying colony at Muncaster Castle. A part of the garden at Ruskin's house, Brantwood, on the east side of Coniston is managed with the species in mind, as are most of the other sites.

Touch-me-not is an annual plant and its numbers fluctuate year by year depending on the degree of successful germination. Its ecology is not well understood; attempts to germinate the seed give poor results. In the natural state it turns up in recently disturbed ground, often at roadsides where vehicles have damaged the edge. Not surprisingly, the Netted Carpet moth has suffered similar declines in abundance.

Research by John Heath (of the ITE) in the 1950's suggested that, in addition to the presence of its foodplant, the Netted Carpet moth requires a habitat having at least 150 cm annual rainfall. His experiments indicated that in drier conditions the pupae died before emergence or pupal emergence was prevented. The yellow-green larvae may be found during the day on the underside of the leaves, well camouflaged by the ribbed veins of the leaf. They feed at night, initially on the leaves but later by biting into the seed pods. Over-wintering occurs as a pupa in a cocoon on the ground.

Netted Carpet Larvae. The image on the left shows the camouflage colour well against the leaf, the Balsam flower and a partly nibbled seed pod. The image on the right shows the larva in a classic "forming a triangle" pose.

I am indebted to Roland Wicksteed of the National Trust at St. Catherine's for permission to use his splendid images.

The National Trust has investigated ways of encouraging the foodplant to grow more successfully, initially by some tree cutting to reduce the shading which has occurred at many sites. A breakthrough in management for the species came when a large population of the host plant was discovered in a wood where over-wintering cattle had trampled the ground. Since 2003, the Trust has managed some of the woodland around Coniston Water with the use of a small number of a traditional breed of cattle, the Blue Grey. When fed supplementary hay scattered in the woodland, the cattle trample the ground. This helps the spread and germination of the seed as long as cattle are removed before germination takes place. New sites managed in this way can also be successful if seed is spread by hand before introducing cattle - where these are near existing populations the moth finds them naturally and will breed there. At one site the number of Touch-me-not-Balsam plants increased from 880 to 56,000 over a four year period, with the result that the number of Netted carpet larvae counted rose from 45 to 500 plus. In 2008 the number of larva counted was the highest since the 1990's; in 2010 the survey of larva at known sites suggested a threefold increase since 2005 and a 25-fold increase in the area to the east of Windermere, all very encouraging and a reward for the efforts of the volunteers involved.

The National Trust is now experiencing considerable success with introductuions and/or strengthening of populations at suitable sites. A new site has recently been discovered at Birthwaite Road. Also in the Windermere area, the plant has been re-introduced at Miller Ground and Stagshaw Gardens and the population at St. Catherine's Wood has been greatly increased - school children willingly trample the ground here instead of cattle! In 2010 Roland Wicksteed was able to report over 200 larvae during a September survey at this relatively small size. At Muncaster Castle the ground is trampled and raked by Owl Trust volunteers. The resultant increase in numbers of plants has led to an increase in annual larva counts from 9 to 269 (in 2010).

The moth is on the wing throughout July and into August, while the plant produces its brown-spotted yellow flowers throughout August. It does best in sunny sites where there has been some soil disturbance.

The small tortrix moth Argyroploce penthinana used to be found on the same foodplant. The dirty white larvae fed and pupated within the stem, from which they could be bred on by collecting the stems in winter. It would be interesting to see whether this species has hung on, as did the Netted Carpet early last century, despite not having been recorded in recent times.

Please report any sightings of the foodplant (or moth).