Yorkshire Status: Uncommon resident.

I seem to have gone into great detail in lockdown in 2020, documenting the decline of this species. Since then, numbers have increased a little, though the vast majority have been from VC61 and it is rare elsewhere. I still haven't had one recently in my garden. It certainly seems to have been lost from large areas of the country, especially in the south and south-east, and the distribution becomes patchier every year.

2020 (CHF): What on earth has happened to Double Dart. In 1883 Porritt said "very common, no doubt everywhere" and in 1907 "abundant everywhere", so it must have been one of the commoner species about at that time. It is not obvious when it started to decline. In 1983, Barry Goater, writing in MBGBI said "occurring rather locally throughout the British Isles; rare or absent in some tracts of apparently suitable county although common elsewhere". In 1989, Sutton and Beaumont looking at the Yorkshire situation said that it was "widely distributed but seldom common" and was more unusual in "the south" and in VC65, preferring woodland on rich calcareous soils. So, in a nutshell, the distribution had become patchy at some time between 1907 and 1983.

Between 1980 and 2000, the population in Yorkshire suffered a huge crash of about 90%, and this is mirrored by the Rothamsted data where the graphs show a major decline until 2000 and then a levelling out. Our Yorkshire population has also levelled out since 2000. Looking at the Atlas it only gives part of the story and simply charts a 95% decline in abundance between 1970 and 2016 without mentioning the sudden fall followed by the plateau which is far more interesting. This is one of the dangers about looking at abundance trends in the Atlas. It is easy to fall into the trap of thinking that a 95% reduction over 46 years means a 2% drop each year, but it masks sudden falls and long plateaus, and this is the same with many species. The rate of change is rarely uniform.

Of equal interest is the change in distribution. Again, the reduction appears most dramatic between 1970 and 2000 with major losses in the south, centre and north-east of England. I see I wrote in 2011 "… has been lost from many areas of central Yorkshire. Numbers in VC61 however have increased and this population is becoming nationally important" and I think ten years down the line this is still very true.

This year's map really emphasises the point. The black dots of past records are thickly clustered in the centre and east of the county, but in 2000, the red dots show all 56 records of 84 moths are clustered in the east. I'm sure we haven't seen the last of it in central Yorkshire. It might not be on its death bed but it's decidedly under the weather. I tend to get it in my garden [Hutton Conyers] on the VC64/5 border every couple of years but I haven't seen it for the last two years. In fact, I haven't seen it anywhere for two years. The VC61 population is interesting. It appears to have crashed earlier than in the rest of Yorkshire but has been relatively stable since 1985 and is doing very well at some sites, though actual numbers have become lower and it's now seven years since we saw over ten in a trap at once.

There seems to be no obvious reason why it has decided to leave central Yorkshire for greener pastures in the east of the county. Perhaps the soils there are "richer and more calcareous". Similar things are happening in other parts of the country. Not a move east, but contraction of larger populations to much smaller areas. It is a moth of broad-leaved woodland and the larvae feed on various broad-leaved trees, so it isn't a fussy eater. Our Field Guide says "long known to undergo cycles of abundance". I'm not sure where it gets that information from as I can't see it mentioned anywhere else. Are we just living through a cycle? If so, it's a rather big one. Wouldn't it be nice to understand what is causing all these different changes with our species! There seem to be all sorts of different patterns and different factors at play. Insects in general are such sensitive indicators of what we are doing to our countryside - far more than birds - and the huge amount of data we are now gathering really should allow us to draw some conclusions. Instead, the more I look at it, the more questions are asked.

Sutton & Beaumont, 1989: Widely distributed but seldom common in vice-counties 61 to 64, but only recorded once from the south and occasionally from the middle of VC65. This species appears to prefer the richer or calcareous soils, and consequently is generally absent on moors and heaths.

Recorded in 108 (54%) of 200 10k Squares. First Recorded in 1845. Last Recorded in 2023. Additional Stats

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