Hampshire and Isle of Wight Butterfly and Moth Society
Hampshire and Isle of Wight Butterfly and Moth Society
| Family: | Lycaenidae |
| Subfamily: | Polyommatinae |
| Genus: | Celastrina |
| Species: | argiolus |
| Authority: | (Linnaeus, 1758) |
The Holly Blue is primarily found in the southern half of the British Isles, and is a frequent visitor to gardens. This species is renowned for fluctuating wildly in numbers, forming a predictable cycle over a few years, believed to be caused by parasitism from the wasp Listrodromus nycthemerus whose sole host is the Holly Blue. The wasp lays its eggs in Holly Blue larvae, with a single adult wasp eventually emerging from the Holly Blue pupa. In England and Wales this species is widespread and common, south of a line running from Cumberland in the west to County Durham in the east. This species is also found on the Isle of Man and throughout Ireland, but is absent from Scotland except as a scarce vagrant.
| #Individuals | #Tetrads | 2022 | 2023 | Abundance Trend | 2022 | 2023 | Distribution Trend |
|---|---|---|---|---|---|
| 4649 | 13013 | +179% | 514 | 723 | +40% |
| #Records | #Individuals | Earliest Record | Latest Record | |
|---|---|---|---|---|
| All Records | 46,776 | 76,451 | 08/01/2019 | 27/12/2020 |
| 2023 | 7,168 | 13,013 | 27/3/2023 | 15/11/2023 |
| Location | Date | Quantity | |
|---|---|---|---|
| Earliest Record | Bitterne | 27/3/2023 | 1 |
| Latest Record | Woolston | 15/11/2023 | 2 |
| Highest Count | Beacon Hill | 16/5/2023 | 50 |
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: 413.28
Average #Recorders: 413.28