This early autumn I am finding Purple Emperor larvae at the rate of one every 2 hours 30 mins, searching as usual in Wilts, Oxon and Glos. That's extremely poor, and it looks as though something has gone very badly wrong. Larvae are as scarce as after wet and windy flight seasons, or scarcer.
In all previous autumns after hot weather flight seasons in which the butterflies were relatively numerous, I've found Emperor larvae at the rate of one every 15-20 minutes. That's the rate I expected when I started this season's autumn searches...
And I'm not finding signs of failed larvae either (e.g. unhatched eggs, egg case bases with no sign of larvae, and vacant seat & feed leaves +/- the old egg case base where larvae have been predated). Normally, I find a fair few of these failed breeding attempts (which I dutifully record).
It may well be that unhatched eggs are no longer around, having come unstuck in the heat (as suggested by the shortage of egg case bases where I do find larvae). Note that there is a known issue with eggs not hatching in heatwaves and Nick & Sam Brownley recorded a number of eggs failing to hatch in Sherwood Forest earlier. I have not recorded eggs coming unstuck before.
Moreover, I'm finding very little else - and I also record moth and sawfly larvae whilst searching the autumn sallows. So, hardly any Pebble Prominent and Clouded Border larvae (just one of each), and no Buff Tips or larvae of the sallow sawflies. Worse, I'm finding no signs of Pebble Prominent larvae beyond, say, about 1/3rd grown - their larval feeding damage is diagnostic, this:-
I am strongly suspecting a catastrophic event, or at least something severe... but whatever has happened is outside my experience.
Caveat: My autumn searches are done from the ground. I haven't been able to climb sallows for several years due to severe osteoarthritis in both knees (I await at least one replacement kneecap). Crucially then, my writings are based on the assumption that (roughly) the same % of eggs is laid low down each year - and there's no data to suggest that this is the case, or isn't...
Much depends on the Dangle Leaf season at leaf fall time (the easiest way to find Emperor larvae in most autumns).
Watch this space...
2 comments:
Hi - is this because of the massive leaf after the "40 degree" event?
Thanks for that comment. I should have said that the places I'm searching were NOT drought affected and that sallow foliage quality there is remarkably high.
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