August is the final summer month, and slowly the light decreases, temperatures drop, and if you look hard enough, you’ll see colour changes in the trees, hinting at autumn. However, a warm August is an excellent month for butterflies. Twenty-seven of our thirty-five species fly during August. The peak population of some of these has passed, but some reach their highest abundance during August.
The Holly Blue, Peacock and Brimstone often show their highest figures in August. The second generation of Wood White (recorded in just 24 out of 1,019 10 km squares between 2010 and 2021) is on the wing in the Burren, and showing high abundance this year. The even rarer Brown Hairstreak, one of Ireland’s rarest butterflies, has been recorded in just 18 out of 1,019 10 km squares between 2010 and 2021. It is now flying, with the first record arriving from Burren National Park on July 31st.
We should celebrate the uplift in Small Tortoiseshell populations this August. Last year was disastrous for this common favourite. The abundance trend during the period 2008-2024 was a decline of 63%. Much of this figure is linked to the collapse in 2024; it was a cold, wet year following a wet summer in 2023. There are many larvae, pupae and adult Small Tortoiseshells in our countryside at the moment; last year, I found no adults in my garden until September, and saw about three individual caterpillars all last year.
Interestingly, I am seeing several Small Tortoiseshell adults in gardens and flower-rich habitats, feeding on nectar. The significance of this behaviour is that it suggests a reproductive diapause applies to these butterflies. These butterflies will delay breeding until next year. Direct-breeding Small Tortoiseshells certainly feed on nectar, but they stay close to nettle beds and exhibit territorial and courtship behaviour. My garden Small Tortoiseshells are not seeking mates. Pre-hibernation feeding is their activity.
That does not preclude breeding by the Small Tortoiseshell now or later this year. Some will likely breed, creating a further, later generation that will fly in September and October. The mechanisms that govern whether Small Tortoiseshells breed directly or delay breeding during early August are probably influenced by conditions such as sunlight levels, temperature, moisture levels, and foodplant quality. These conditions vary across the landscape. For example, the local climate in the Howth area on the Dublin coast is drier than it is thirty-five km inland, in south Meath. In Howth, nettles lack the moisture and nutrient content of those growing in heavier, more fertile soils inland. Frank Smyth, who has observed the Small Tortoiseshell in Howth for decades, has noticed that it has abandoned the second generation in most years.
In South County Meath, Small Tortoiseshell larvae have been recorded at various times from May 13th to August 4th. Looking at the dates it has been found, it is possible that the species has produced three generations there in 2025.
In its nettles, the Small Tortoiseshell caterpillars are in company with Red Admiral larvae. These live singly, concealed with folded leaves. The adult Red Admiral is showing in good numbers, and breeding is still taking place. The larvae are polymorphic. Some are mainly black, some green, and others a mixture of colours.
The Holly Blue is showing in its second generation at the moment. This generation relies mostly on Ivy for breeding. This generation flies well into September. Those flying in late September and October might represent a third generation.
The white family of butterflies continue to fly in high numbers. The three common whites, the Large White, Small White and Green-veined White, continue to grace our gardens and wilder places. The Brimstone has its second peak of the year during August; the first peak is in April.
Finally, the brown family of butterflies contains common and rare species, and one endangered species. The Wall Brown is endangered, now largely restricted to grassland on the most nutrient-poor, free-draining soils near and among rock outcrops. The second generation peaks this month. Sadly, your chances of seeing it are so much reduced from what they were thirty years ago.
Finally, an intriguining development has just been reported from England, where the Southern Small White Pieris mannii has finally arrived from the continent. This butterfly has expanded rapidly from its chief traditional breeding grounds in the southern and southeast Mediterranean, reaching Calais by 2019. This species breeds on Candytuft, Iberis sempervirens and Rock Candytuft Iberis saxatilis, not native but widely grown in gardens.
Looking very like our Small White, it can be separated by the forewing upperside’s apical patch. In the Small White, this extends further down the costa than down the outer edge. In the Southern Small White this patch extends as far down the outer margin as it does along the costa. Will this butterfly cross the Irish Sea? It was recorded on August 2nd in Languard Nature Reserve, on the Suffolk coast. This site is about 123 km from the French coast near Dunkirk. If the Southern Small White migrated this distance, it is certainly capable of reaching Ireland from Britain across the Irish Sea, which in many places is significantly less distant. It could be capable of reaching Ireland from the continent using the following southerly wind.
It might be in Ireland already. It is well worth looking at all ‘Small Whites’, especially in coastal areas in the south and east. We would be happy to check any photographs sent to us by email at conservation.butterfly@gmail.com
References
Harding, J. & Lysaght, L. (Eds.) (2025) An Atlas of Butterflies in Ireland 2010-2021. The National Biodiversity Data Centre, Waterford.
Judge, M and Lysaght, L.(2025) The Irish Butterfly Monitoring Scheme Newsletter, Issue 17. National Biodiversity Data Centre.