Small White

Pieris rapae

General Distribution and Status

The Small White is a widespread and common butterfly throughout Britain boosted by immigrants from Europe. It appears that the butterfly did not suffer as badly as the Large White after the last war by the increased intensification in agriculture and pesticide use. It was found that application of pesticide, DDT, killed off an increased number of larval predators such as ground beetles and harvest spiders resulting in an increased number of larvae later in the season (Heath et al.). Numbers have dropped by about a quarter since 1976 but have stabilised since 2009 in spite of a poor run prior to 2018 which was a spectacular year for the butterfly (Brereton et al.). In Hertfordshire and Middlesex, only since 2011 has the Small White recovered up to the level of the mid 1990s in terms of abundance which may be due to the heavy presence of oil-seed rape in the county (Wood, 2012).

UK distribution map
UKBMS Species summary (2020)

Habitat Requirements

The species is found in most habitats but more so on waste ground, gardens and allotments where cultivated brassicas are grown. Fields containing oil-seed rape are also frequented.

Larval Foodplants

Cabbage Brassica spp., Water Cress Rorippa nasturtium-aquaticum. Hedge Mustard Sisymbrium officinale, Garlic Mustard Alliaria petiolata, Hoary Cress Cardaria draba and Wild Mignonette Reseda lutea are also sometimes used (Sawford).

Adult Food Sources

Buddleia Buddleja davidii (685), Garden Lavender Lavandula x intermedia (299), Horseradish Armoracia rusticana (94), Creeping Thistle Cirsium arvense (94), Bramble Rubus fruticosus agg. (91). Burdock Arctium spp. and Black Horehound Ballota nigra are also mentioned (Wood 2016).

Historical Records

It seems that the Small White has always been very common in Hertfordshire. For instance, Foster in 1934 describes it as 'generally abundant' and in 1959 there were reports of third brood specimens (Bell). I did not find any evidence of dwindling numbers in the county up to the 1970s and like most species the 1976 drought had an adverse affect with populations plummeting in the following year.

Local Distribution and Abundance

The Small White is present in every tetrad as shown on the map. Good numbers occur at Great Ashby Park, Knebworth Park and Fairlands Valley Park. The latter is not necessarily the best place to find it as indicated on the map since far more visits were made to the site although over 50 individuals were counted on the same date, 24 July, in both 2004 and 2013. Estimates of 100 specimens were recorded at Astonbury Wood on 13 August 1997 and at Cherrys Farm in Weston on 19 August 1997. More reports of this butterfly (415) were submitted in 2020 than any other year in the survey period although abundance was not as high as in 2018 when populations reached a peak in the first half of July perhaps suggesting that there was a large influx from the Continent. Again, over 400 reports were received in 2021 and good numbers seen particularly in the latter half of July. However, 2022 saw a significant reduction in abundance especially from August onwards which probably led to small numbers emerging in the following spring in 2023. The summer brood was similar to the numbers in 2022.

Transect weekly counts

Stevenage (South Fairlands Valley Park) transect 1993-2023

Like the Large White a warm and dry summer does not necessarily mean there will be a higher number of Small Whites flying. The best season was in 2004 when there was a cool and wet summer although the last week of July brought in dry and humid air from the Continent which could have led to an increased migration to the UK. A combined count of about 100 specimens was recorded on 24 and 31 July 2004.

Knebworth Park transect 1996-2010 and 2017-2023

2018 turned out to be an incredible year for the Small White here, the best ever during the survey. There was a good first brood in May, and numbers jumped significantly in the second brood perhaps partly due to the fine weather in June, to reach nearly 100 on 9 July, nearly half of which were found at Burleigh Bottom at the northern tip of Graffidge Wood.

Knebworth Woods transect 2017-2023

Numbers nearly doubled in 2018 with a count of 33 on 16 July. Abundance was considerably lower in 2021 and 2022.

Pryor's Wood transect 2000-2022

Numbers are relatively stable although in 2016 and 2017 only five individuals were recorded in all. 2008 was the best year with a count of 18 although the highest weekly count was 11 on 24 July 2004. Only three were seen in 2022.

Life History

Earliest date: 16 March 2014 at Walkern
Latest date: 28 October 2016 at Roebuck

Any warm weather in early spring should accelerate development of the overwintering pupae and adults emerge by early April. The second generation is always larger than the first based on results in this survey and is bolstered by Continental immigrants but it is unknown if the immigration is the only or major cause. The sighting on 28 October in a garden in Roebuck in 2016 is the latest ever record in the Stevenage area. Eggs are laid singly on a number of wild foodplants under a leaf. Larvae eat the leaves leaving characteristic holes. When fully grown, they move away from the foodplant to pupate on tree trunks, fences and buildings.
More details on the UK Butterflies website

Behaviour/Observation notes

The Small White is probably the most common 'white' to visit gardens to feed on flowers. In hot and dry weather, aggregations may be found imbibing minerals from mud. It can be confused with the Green-veined White in flight but to the trained eye it might be possible to differentiate them by their behaviour. Small Whites tend to make more purposeful flights but this is by no means a reliable guide. Another clue is the habitat; if it is a damp or shady place it is more likely to be a Green-veined White but again not a hard and fast rule.

Variations/Aberrations

Variation in the ground colour of the uppersides and the extent of the dark markings are the main aberrations but these are rare and most apparent in Scotland and Ireland.
Find out more on the UK Butterflies website