Hampshire and Isle of Wight Butterfly and Moth Society
Hampshire and Isle of Wight Butterfly and Moth Society
| Family: | Nymphalidae |
| Subfamily: | Nymphalinae |
| Genus: | Aglais |
| Species: | urticae |
| Authority: | (Linnaeus, 1758) |
The Small Tortoiseshell is one of our most-familiar butterflies, appearing in gardens throughout the British Isles. Unfortunately, this butterfly has suffered a worrying decline, especially in the south, over the last few years. This butterfly has always fluctuated in numbers, but the cause of a recent decline is not yet known, although various theories have been proposed. One is the increasing presence of a particular parasitic fly, Sturmia bella, due to global warming - this species being common on the continent. The fly lays its eggs on leaves of the foodplant, close to where larvae are feeding. The tiny eggs are then eaten whole by the larvae and the grubs that emerge feed on the insides of their host, avoiding the vital organs. A fly grub eventually kills its host and emerges from either the fully-grown larva or pupa before itself pupating. Although the fly attacks related species, such as the Peacock and Red Admiral, it is believed that the lifecycle of the Small Tortoiseshell is better-synchronised with that of the fly and it is therefore more prone to parasitism. This is one of our most widespread butterflies, occurring throughout the British Isles, including Orkney and Shetland.
| #Individuals | #Tetrads | 2022 | 2023 | Abundance Trend | 2022 | 2023 | Distribution Trend |
|---|---|---|---|---|---|
| 3130 | 2386 | -23% | 530 | 506 | -4% |
| #Records | #Individuals | Earliest Record | Latest Record | |
|---|---|---|---|---|
| All Records | 46,496 | 106,322 | 05/01/1999 & 2018 | 25/12/2013 |
| 2023 | 1,545 | 2,386 | 6/2/2023 | 7/11/2023 |
| Location | Date | Quantity | |
|---|---|---|---|
| Earliest Record | Kings Park | 6/2/2023 | 1 |
| Latest Record | Godshill | 7/11/2023 | 1 |
| Highest Count | Bucklers Hard | 31/7/2023 | 20 |
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: 379.6
Average #Recorders: 379.6