Friday, December 30, 2022

Prospects for 2023...

Happy New Year to all of Purple disposition...

I'd like to say that the prospects of an annus mirabilis year for the Purple Emperor are looking good, but they're not - at least, not at this stage. 

Autumn larvae were scarce everywhere. We think because 1) the egg lay was low, due to females being stressed by extreme heat; 2) many eggs failed to hatch - they boiled in the bag instead [as happened in Sherwood Forest]; 3) many young (L1) larvae desiccated in the mid-July and early August heatwaves [as has happened before, e.g. in 1976 & 1989].  

In Savernake Forest, Wiltshire, autumn larvae were at the second lowest level I've recorded in 14 years of standardised searching. On the Lambourn Downs, SW Oxon, autumn larvae were a third of previous levels (it's a Year 4 study site). In Cirencester Park Woods, Glos, (a new colonisation, in Year 2), larval numbers were down by 50%. And I've searched assiduously in all these sites.

And the big one, Ben Greenaway has found that larvae are 50% down in his major study area just up the road from Knepp in W Sussex (though in part due to habitat deterioration).

In addition, I noted a severe paucity of the sallow-feeding moth and sawfly larvae I find in the autumn, as bycatch, everywhere. There seems to have been a mass failure of things like Pebble Prominent (which has distinctive larval feeding marks).  

That's the bad news...

The good news, is that Great Tit numbers appear to be well down. They, and other titmice, seem to have suffered from the cold spring and, possibly / probably the impact of the heatwaves on insect food sources. Great Tits are major predators of hibernating Emperor larvae. I'm trying to get some info from the ornithologists on this... (Bird Garden Birdwatch should provide a good pointer). 

Also, the severe cold snap in early December should have taken out various invertebrate predators which thrive in mild winters.

So, there is Hope... 

Other key life stages determining adult numbers are the pupation period and pupal period, which we're just starting to study properly. There seem to be major losses during these stages, suggesting that the shorter time the insect spends pupating and as pupa, the more Emperors fly. 2022 had poor weather during that period (remember the Jubilee downpours).  

One prediction I will make, is that the 2023 Purple Emperor season is unlikely to start before Midsummer Day (unless we get a long fine spring and a wonderful June) - because the sallows will over-flower next spring, and leaf late, in response to heat & drought stress.

Here's Larry The Cat(erpillar), one of 8 I'm following locally - 

And here's a rather coy Boris 3rd -