Hampshire and Isle of Wight Butterfly and Moth Society
Hampshire and Isle of Wight Butterfly and Moth Society
| Family: | Nymphalidae |
| Subfamily: | Nymphalinae |
| Genus: | Nymphalis |
| Species: | polychloros |
| Authority: | (Linnaeus, 1758) |
In Victorian times the Large Tortoiseshell was considered widespread and common in woodland in southern England. However, this beautiful insect has since suffered a severe decline and there have been less than 150 records since 1951. This butterfly, whose numbers were always known to fluctuate, is generally considered to be extinct in the British Isles, with any sightings considered to be migrants from the continent or accidental or deliberate releases of captive-bred stock. Several causes of its decline have been suggested - including climate change, parasitism, and the effect of Dutch Elm disease on one of its primary foodplants. The hope, of course, is that this butterfly is able to once again colonise our islands. Although previously found in many parts of England, Wales and Scotland, the greatest concentrations were in the midlands, south and east of England. This species has not been recorded from Ireland. Recent sightings have come from the south coast, in particular from South Devon, South Hampshire, the Isle of Wight and West Sussex.
| #Individuals | #Tetrads | 2022 | 2023 | Abundance Trend | 2022 | 2023 | Distribution Trend |
|---|---|---|---|---|---|
| 5 | 11 | +120% | 4 | 10 | +150% |
| #Records | #Individuals | Earliest Record | Latest Record | |
|---|---|---|---|---|
| All Records | 145 | 160 | 10/02/2008 | 04/09/2021 |
| 2023 | 11 | 11 | 3/4/2023 | 17/7/2023 |
| Location | Date | Quantity | |
|---|---|---|---|
| Earliest Record | Walters Copse, Newtown | 3/4/2023 | 1 |
| Latest Record | Portsmouth | 17/7/2023 | 1 |
| Highest Count | Walters Copse, Newtown | 3/4/2023 | 1 |
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: 3.92
Average #Recorders: 3.92