Tuesday, March 8, 2022

Greening up, and getting crunched

  Purple Emperor larvae are greening up nicely at the back-end of yet another mild winter - at least, those that haven't been predated.

  Predation, seemingly mainly by birds and particularly by tits, is a major hazard during the five month-long diapause (which we call hibernation).  In most winters, about two-thirds are lost.

  This winter, Ben Greenaway seems set to lose 2/3rds (or maybe even 3/4s) from a sample of 40 in woods north of Knepp in West Sussex, and I seem set to lose about 2/3rds from much smaller samples in Savernake Forest, Wiltshire, and a small ancient woodland site on the Lambourn Downs.  I had hoped for less...

  The good news is that, to date, I have only lost one out of eight larvae in a new breeding ground in part of Cirencester Park Woods, Glos.  That's remarkable, though it may yet end in tears.  Tit populations, as measured, are relatively low in these woods (lack of nesting holes in plantation woodland) and it may be that the tits simply haven't discovered Emperor larvae on the sallows, in new sallow stands that only started to become suitable during 2021.  

  But Ben has had some losses to invertebrate predation, by some type of sucking bug (shield bugs, he thinks), and yesterday I found this had happened to one of the larvae I was following on a dead twig in Savernake - 

  You can see the hole plainly.  I have followed some 200 larvae in the wild through the last 13 winters but hadn't noticed this sort of loss before, though I had a number apparently shrivel up during the mild winter of 2013-14, some of which may have been sucked (only I didn't detect the pierced hole, which may only show up for a short while).  This may be a problem associated with mild winters...

  Meanwhile, here's a healthy larva, sleeping the final days of winter, dreaming up the spring, and scheming of flying the golden high summer skies - 

  And here's another from yesterday, starting to get some protection from swelling, silvering flower buds -