Southern Small White - An Identification Guide
by James Corton, County Recorder for Butterflies, Suffolk (August 2025)

Introduction

The Southern Small White (Pieris mannii) was first confirmed in the UK on 2nd August 2025 at Landguard Bird Observatory in Suffolk by Chris van Swaay using photographic evidence supplied by Will Brame.  It sparked a great deal of interest from wildlife enthusiasts.  A large influx of white butterflies has occurred this year in successive waves throughout June and July, mostly on the east coast, with some waves numbering into the hundreds of thousands.  In mainland Europe, for every Southern Small White there are reportedly 10,000 Small White.  In an ‘invasion year’ such as 2025 there could be hundreds of Southern Small White in the UK already—and now people are looking out for them.  At least one more has since been confirmed.

As County Recorder for Suffolk, I have been involved and had a busy few days with social media and through my County Recorder emails.  The queries received has led to this field guide being compiled with the help of ten years of field experience from Chris van Swaay and his photographs of ‘typical’ Southern Small White butterflies at various times of year.  Variation occurs which makes identification even harder so I will concentrate on typical adults only.


Identifying Features of the Southern Small White

Females are perhaps easier to separate from other whites than the males.  The species can have three generations a year and markings vary both between generations and individuals.  To keep things as simple as I can I’ll describe the typical spring brood features and then the summer/autumn brood features which differ from this.

Southern Small White female, Spring brood, Netherlands. ©Chris van Swaay

Spring brood features: 1. Heavy dusting of blackish pigment across much of the wings   2. The apical patch is large and extends down one third of the wing margin, level with the discal spot   3. The discal spot is large and squared, often with a concave outer border 4. Sometimes there is an additional discal spot on the hindwing which can be reduced to a smudge and is often paler 5. The outer wing margin is noticeably curved compared to the straighter margin of the Small White

Summer and autumn broods have much more contrast.  The discal spot is even larger, sometimes spilling over the veins—a feature not found even in well-marked Small White.  As with the spring generation, it is square-like and often concave on the outer edge.  Some females have both forewing spots joined by a bar of black scales and/or another discal spot, on the upperside hindwing (see Will Brame’s photograph).  This also rarely occurs in Small White females.

Southern Small White female, summer brood, Netherlands. ©Chris van Swaay

Summer brood features: 1. Markings are darker in summer and autumn broods and more extensive than in the Small White   2. The discal spot is still large, square-like and often with a concave outer edge—sometimes so large it spills beyond the boundary of the wing veins

The caterpillar looks similar to the Small White but has a dark head in its early stages and feeds on Perennial Candytuft Iberis sempervirens, Inflated Bladderseed Alyssoides utriculata and probably related plants also.  The pupa is whitish and sometimes fused with red and lacks any black markings. By contrast, the Small White pupa is greenish and has black markings.

Similar Species

Large, Small and Green-veined White are all in some ways similar to the newly arrived Southern Small White. 

Large White are the easiest to separate, being larger and the wing markings are quite different when observed.  The apical patch extends down the margin a long way (two thirds) and males have no discal spot.  Females have two large forewing spots but these are rounded.

Green-veined White can resemble Southern Small White on the upperwings but the discal spots are rounded and their veins blackened.  Additionally, the apical patch is broken and continues down the margin much further than in Southern Small White.

The Small White is the species most likely to be confused.  It varies quite a deal and can appear similar to Southern Small White.  Individuals maturing during hot weather appear darker with more black pigmentation of their wings, including extended apical patch and larger spots—but not the very large and square-like spots of typical Southern Small White.  They are also rounded and not concave on the outer edge.  There is an overlap in markings due to variation in both species where it is impossible to identify with certainty and this will affect recording.  

Flight

Some similar looking whites have characteristic flight patterns which help to identify them.  For example, Clouded Yellow, including the whitish helice form, have a bobbing flight which makes them stand out from other whites.  The Southern Small White also has a different flight and it has been likened to the dainty flight of the Wood White.  

Requirements for Acceptance of Records

Butterfly Conservation has requested the species be added to the iRecord database so that users can record sightings.  The species is new to the UK list and we are all inexperienced with it.  Additionally, there is overlap with the very variable Small White.  So, we as County Recorders will be looking for diagnostic features which typical specimens will possess.  Ambiguous records will probably not be acceptable because we have to be certain in order to keep accurate data on the occurrence and spread of a new species.  These can be recorded still, at genus level as Pieris species or Small White. 
In conclusion, all records should be accompanied by one or more photographs before they can be verified and confirmed.

Southern Small White, female, summer brood. ©Will Brame

The first Southern Small White recorded in Suffolk Note the curved wing margin. There is also a black wing bar connecting the two forewing spots (not always present). The discal spot is large and square and the apical patch travels along the costa and margin equal distances (approximately one third of the margin length)