The Butterflies of Essex
2024 Year in Review
Brown Argus Aricia agestis
Summary
The Brown Argus is of Least Concern in the vice-counties of North and South Essex, and is considered the lowest priority when it comes to butterfly conservation. It is regarded as one of the success stories of butterfly species within Essex with its range increasing since the 1990s, which is surprising since Essex has next to no chalk downland or the associated larval food source Common Rock-rose
Helianthemum nummularium. It seems to have adapted utilising a variety of cranesbill, notably Common Stork's-bill
Erodium cicutarium and Dove's-foot Crane's-bill
Geranium molle which are common and aggressive self-seeders regarded as "weeds" in Essex. They will form large patches after any soil disturbance and within nutrient-poor soils with bare soil both of which are free from rank grass providing ideal habitat for Brown Argus. This includes field margins, road verges, and the sloping, open grasslands along the sea walls. In 2023 they had a boom year but this was followed by a disappointing year in 2024 where they were notably missing early in the year during the wet, cloudy spring and early summer but recovered a little during late summer. This seems to be the case in most of the UK.
iRecord sighting records provide spatial and temporal distribution for the whole of the UK which suggests that the Brown Argus can be seen in every hectad in Essex:
- Brown Argus UK Spatial & Temporal Distribution
Source: iRecord
It gives a false impression that Brown Argus can be seen throughout Essex but this is not so. They are colonial and are restricted to open ground habitats on free-draining, nutrient-poor soils where small, compact colonies are the usual sightings within Essex. The Essex Field Club hectad distribution map shows that they are most common towards the south-east of the county. Most of the areas where sighting records are missing are low population density agricultural land on nutrient-rich soil:
- 1990-2023 Brown Argus Hectad Distribution Map
Source: Essex Field Club
The
spatial distribution map limited to all the recorded sightings on the
iRecord website is as follows:
- Brown Argus Spatial Distribution Map
Source: iRecord
It is not surprising that the build up of distribution maps from 2005 to 2024 reveals more about the transference of data collection from paper to digital methods, notably the mobile apps. It shows little about the Brown Argus.
- 2005-2014 Brown Argus Spatial Distribution Map
Source: iRecord
- 2015-2024 Brown Argus Spatial Distribution Map
Source: iRecord
What is more revealing is the comparison between the spatial distribution maps for 2023 - a successful year - and 2024, which is generally regarded as a poor year:
- 2023 Brown Argus Spatial Distribution
Source: iRecord
- 2024 Brown Argus Spatial Distribution
Source: iRecord
The difference in the number of locations where Brown Argus sightings were recorded are strikingly different with a significant reduction in sites from 2023 to 2024, perhaps by 2/3rds. It is especially notable that recorded sightings in the north-east London area are almost non-existent in 2024.
Not surprisingly the
2024 abundance of the Brown Argus within Essex, limited to recorded sightings on the
iRecord website is less than a third of those recorded in 2023:
- 2023-2024 Brown Argus Temporal Distribution
Source: iRecord
The
abundance by location for 2024 is significant as it shows where the most recorded sightings occurred and these closely correlate with experienced recorders predominantly collecting data via transect walking. The standout site by a long way is Wallasea Island.
- 2024 Brown Argus Abundance by Location for all records
Source: iRecord
I think what is more significant is the lack of recorded sightings, via iRecord, including transect data from the UK Butterfly Monitoring Scheme, from very notable sites that you might expect more from even within a bad year. Some sites do not even register double figures throughout the flight period. Double figures were only recorded four times for a site visit, three of which were at Wallasea Island and one was one of my visits to Benfleet Downs. Wallasea Island, Benfleet Downs, and my own local patch Baddow Meads had significantly more recorded sightings than anywhere else in Essex with Wallasea Island 5 times greater than Benfleet Downs in second. Quite remarkable.
I can confidently say that Wallasea Island is the place in Essex to see Brown Argus.
My own recorded sighting data, not surprisingly, correlates very closely to all data collected for 2024 via
iRecord. This is because Wallasea Island, Benfleet Downs, and Baddow Meads - the top 3 locations - are three of the sites that I visit regularly, not that I was searching for Brown Argus. I also include the fourth site on that list, Great Holland Pits, but I did not record a single sighting of a Brown Argus - I think for the first time.
- 2024 Brown Argus Abundance by Location DL
Source: iRecord
And my abundance by date of recorded sightings was very similar to the temporal distribution of all recorded sightings with the majority of sightings during August and into autumn. I only saw 6 Brown August during May and June out of a total of 102, which is by no means a small amount of sightings given the total for all sightings in Essex was 475. I saw roughly one fifth of the total without hardly seeing a Brown Argus before the first week of August.
- 2024 Brown Argus Abundance by Date DL
Source: iRecord
- 2024 Brown Argus Abundance by Month DL
Source: iRecord
My first sighting of a Brown Argus in 2024 was on the 23rd of May on my local patch within Baddow Meads which was to be the only place I saw one with another couple of sites within Chelmsford and mid-Essex until mid-August, when I finally saw my first one somewhere else. My highest daily total of 18 was on the 28th of August during a site visit to Benfleet Downs closely followed by 16 the next day at Wallasea Island. My final sighting was on the 04th of October, during my trek around the Essex Saltmarsh Coast, at Marsh Farm Country Park. The lack of sightings around the sites I visited within Essex was sad.
Highlights
Not many, to be honest - just a feeling of real disappointment. I am particularly sad, actually heartbroken, that I did not manage to see one Brown Argus at my little meadow in Meadgate Fields Open Space which probably means the local extinction at that site.
Nearly double figures last year, and always in the same place, to none.
The best days I spent with this little beauty were obviously the late August trips to Benfleet Downs and Wallasea Island when there was an unexpected explosion of activity - but it only lasted a week before they disappeared again. And the courtship of the only 2 I saw all year at Hatfield Forest was a delight. I am just praying they have an excellent year during 2025 and expand their range once again in Essex.
