Mid August '26: Larval Progress & the State of the Nation's Sallows

These are challenging times for Purple Emperor larvae in the wild, with heatwaves impacting on larval development and the ongoing drought affecting sallows and foliage quality.

In and around Savernake Forest, Wilts, larvae are developing steadily and the sallows are holding up relatively well, for now. 

We have equalled the mid-August record for the earliest 3rd instar larva (set in 2018). All other larvae this last weekend (15th-16th) were in the 2nd instar, mainly in mid-L2 state. 

As yet, there are no signs of larvae developing way ahead of schedule, and threatening to double-brood (and we don't want them to to that anyway, it's a waste of butterflies). 

To date, larval losses have not been severe, or as high as they were this time last year. That may be because the females have laid in deeper shade this year, and/or because the heat may have reduced predator numbers significantly. 

However, here's a dead 2nd instar (L2) larva found there yesterday - 

This individual may have died in the heat, shrivelling up soon after changing skin (as can happen), or it may have been attacked by a predatory sucking bug (the Red-legged Shieldbug, a vicious predator of small caterpillars, has increased phenomenally on sallows in Savernake in recent years). But overall, larval survival is reasonable.  

Here's a nice late L2 larva from yesterday -

Numbers-wise, larvae seem to be locally good in the forest, but distinctly patchy, with some breeding areas being surprisingly neglected - but it's early days in the survey season. 

The problem here is that the Empress is forever moving the goalposts, adopting different laying strategies from year to year, and it takes us a while to crack what she's been doing. Her only consistency is her sublime disregard for our botanical taxonomy - she does not use Clive Stace's New Flora of the British Isles (2019, 4th edition) let alone Meikle, R. 1984. Willows & Poplars of Great Britain & Ireland. Note that the vast majority of sallows I find larvae on key out as hybrids (mostly as x Reichardtii hybrids).  

Some districts have had no effective rain since June 11th (after a very wet start to the month). Wisley, Surrey, has just recorded 60 rainless days. Sallows in free-draining situations are dropping leaves (e.g. Cotswold Water Park [gravels] and on the Lower Greensand). Savernake's sallows are largely holding out well, but for how much longer...?

We need a Ministerial Statement on the State of the Nation's Sallows...