A key to the identification of Pyrgus species has been produced by Cédric Jacquier in January 2017. It uses photographs from this site and leads through a series of logical steps to eliminate certain species and narrow down the options to one species. It is in French but is largely visual, so hopefully quite usable even for those with no/limited French. Many thanks to Cédric for producing this valuable resource. The key can be accessed here: http://files.biolovision.net/www.faunegeneve.ch/pdffiles/news/PyrgusKey2017v11-7022.pdf
There are 14 species of Pyrgus which occur in France, using the revised taxonomy that classifies malvae and malvoides as separate species. Most of these species occur widely in Europe and there are only an additional two European species of Pyrgus that do not occur in France.
These 14 species are alveus, andromedae, armoricanus, cacaliae, carlinae, carthami, bellieri (foulquieri), cirsii, malvae, malvoides, onopordi, serratulae, sidae, warrenensis. As malvae and malvoides are inseparable from external characteristics alone, they are treated as one species here, although it is probable that all are in fact malvoides (http://www.butterfliesoffrance.com/html/Pyrgus%20malvae.htm). Only alveus has a significantly different subspecies in France, centralhispaniae which occurs in Spain and Italy as well as (it is believed) in the French Alpes, although this could be the form accretus; information seems scant on this.
identification from markings
Confident identification is sometimes extremely difficult, and often impossible, from external features alone. Identification from an upperside view alone is more very much more difficult than from the underside, where the colouring and size and shape of (some of the) hindwing (unh) markings is often described as characteristic, a word used to signify a mark or combination of marks which is unique to that species. Photographs of what are believed to be representative undersides can be found here.
The upperside colouring and markings follow a broad pattern for all Pyrgus, and whereas the markings may be stronger or weaker, there is only a limited degree of the uniqueness of these markings. Only a few species could be identified with confidence from the upperside alone. Photographs of what are believed to be representative uppersides can be found here.
The leading publications often quote a key feature or features for a particular species. Whereas these may sometimes be conclusive, natural variation means there are many occasions where these features may not be quite as clear-cut as the publications would have you believe. Also, the natural variation of other species may result in some degree of overlap of these key features. The comparative chart for the upperside colouring and markings, plus size, flight period, altitude, is given here. Distribution has not been included. This chart has been compiled from the leading publications, which are more or less in agreement.
Some Pyrgus species can be identified with a greater or lesser degree of confidence, although seven geographically-overlapping species can be confusingly similar and these are the species primarily of concern here: alveus, armoricanus, carlinae, bellieri (foulquieri), cirsii, onopordi, serratulae.
The remaining seven species (andromedae, cacaliae, carthami, malvae, malvoides, sidae, warrenensis) all have significant features to facilitate identification (to a greater or lesser extent) are not being studied in detail in this review (summary of their uns features is given here). These species may be included when the study of the “difficult 7” has been completed.
Other identification factors
There are a number of factors best described as environmental, e.g. location, altitude, and flight period, which are strongly indicative and may serve to eliminate some options but may only occasionally be considered definitive. Identification of a Pyrgus species by the elimination of all others may have appealed to Sherlock Holmes (when you have eliminated the impossible, whatever remains, however improbable, must be the truth), but is hardly convincing.
Object of this review
This review focuses on the combination of the unh markings to provide definitive, or least highly probable, identification. The Pyrgus unh is divided by the veins into eight broad horizontal sections numbered s1 to s8; some of these veins emanate directly from the basal region, others such as s3 and s6 occur from a division in the discal region. s1 is technically s1c as space 1 is comprised of three sections, s1a and s1b being normally not visible when the Pyrgus is a rest with the wings closed. The veins are also numbered. The white markings are arranged in three bands, sometimes complete and sometimes not, and are broadly described as marginal, discal and basal. The illustration is given here.
This review is principally concerned with the uniqueness and degree of consistency of these unh markings and their value in producing confident identification. The leading publications have limited illustrations of Pyrgus undersides and in several cases are conflicting. The leading trusted web sites also have very few examples of Pyrgus undersides. The ultimate key will be the study of large numbers of correctly-identified specimens to determine the reliability of certain features and their range of variation.
The UK Natural History Museum (NHM) archives were studied in March 2011 and a detailed study was undertaken of the markings of the unh of the difficult 7. Unfortunately, about 90% of the archive specimens were ups (which were not removed from the cases) and so this exercise was of limited value. In the summer 2011 a concerted effort was made to photograph both upper and undersides of as many Pyrgus as possible, to enhance the chances of correct identification.
As a result, the chart comparing the unh markings for the difficult 7 has been updated and can be viewed here; this is an attempt to produce a “weighted” marking scheme where the markings have differing values for each species and under a “totting up” mechanism, reaching a combined total (of 100) is considered adequate for identification. Key:
1. a green box suggests a sufficient degree of consistency to enable the assignment of a weighted score
2. a yellow box indicates it is within the range of variation of this species, but not considered indicative
3. a red box indicates that the feature described would preclude that species.
In the course of studying these unh markings, a number of observations arose. These are given here for interest and possible comment.
This is an ongoing process, further photographs will be collected and input is actively invited on any aspect; please respond either by direct email or via the contact box.