Hampshire and Isle of Wight Butterfly and Moth Society
Hampshire and Isle of Wight Butterfly and Moth Society
| Family: | Lycaenidae |
| Subfamily: | Polyommatinae |
| Genus: | Plebejus |
| Species: | argus |
| Authority: | (Linnaeus, 1758) |
The Silver-studded Blue gets its name from the light blue reflective scales found on the underside of most adults and which are quite visible when light reflects off them. As with many other species of blue, the males are blue while the female is a less-conspicuous brown. However, this butterfly is highly variable in appearance and, as stated in Dennis (1977), variation extends to "differences in the male upperside coloration, the width of the marginal border (wide in the New Forest, narrow in Devonshire) and the underside grey coloration (dull grey in the New Forest, silvery grey in east Suffolk); in the female to the development of the blue coloration and the orange lunules on the upperside, and on the underside to the coloration, the width and prominence of the medial white band".
Both Worms (1949) and Thomas (1999) provide an analysis of many populations found in the British Isles, all of which are considered to belong to the nominate subspecies by default, despite apparent differences in appearance. This includes populations found on mossland at Llyn Hafod-y-llyn in north Wales, on limestone at Portland Bill in Dorset, at Holy Island off Anglesey, at Prees Heath in Shropshire, and on the sand dunes of south-west England.
This delightful butterfly is found in close-knit colonies, with individuals rarely flying any distance. Most colonies contain less than a thousand adults. However, a few colonies are huge, with the number of adults measured in tens of thousands, providing an amazing spectacle. Most colonies of this species are found in southern England, although there are several other notable colonies in the east of England and Wales. With the exception of a single site at Prees Heath in Shropshire, this butterfly is absent from central and northern England, Scotland, Ireland and the Isle of Man.
| #Individuals | #Tetrads | 2023 | 2024 | Abundance Trend | 2023 | 2024 | Distribution Trend |
|---|---|---|---|---|---|
| 8953 | 6987 | -21% | 100 | 86 | -14% |
| #Records | #Individuals | Earliest Record | Latest Record | |
|---|---|---|---|---|
| All Records | 10,789 | 160,271 | 09/05/2011 | 30/10/1921 |
| 2024 | 786 | 6,987 | 25/5/2024 | 3/9/2024 |
| Location | Date | Quantity | |
|---|---|---|---|
| Earliest Record | Broxhead Common | 25/5/2024 | 2 |
| Latest Record | St Ives | 3/9/2024 | 1 |
| Highest Count | Sopley Common | 27/6/2024 | 158 |
One of the issues with 'raw' trend data is that there is inherent bias based on the number of recorders. For example, the number of individuals and populated tetrads recorded are likely to increase if there is an increase in the number of recorders. In order to remove this bias, the normalised trends use data that has been recalculated using the average number of recorders over the trend period. This normalisation gives a much better picture of the true trends.
Average #Recorders: 67.64
Average #Recorders: 67.64