In my own experience I am finding that there is still lots of fresh, lush nettle growth on sheltered sites which was unaffected by the recent cold spell. Certainly on more exposed sites it's a completely different story, but I don't think that the butterflies would have laid eggs there in the first place. Ultimately, temperature is bound to be a determining factor in the supply of nettle and the survival rates of eggs and larvae. The effects of this would be more noticeable as you move further north in the country, but there are likely to be a combination of factors involved. In southern and coastal areas it looks like the larvae are tough enough to survive extended periods of cold weather, particularly the early instars which can move to the base of the plant and hunker down between the tightly packed new growth. I have found that the later instars (4th and 5th) have a harder time in the cold weather. Of the many eggs laid in mid-September 2017, which hatched around 30th September, only one sluggish 5th instar survives, despite having a ready supply of food plant. The eggs are also tough, but I don't believe that they can survive to such low temperatures as the larvae. The other limiting factors for eggs appear to be predation and the fact that after a period of time the leaves on which they are laid will shrivel over the winter and drop to the ground making them more vulnerable to loss. I do not have enough data to comment on likely survival rates of pupae and it's really going to take a proper scientific study to draw all of these strands together.Pete Eeles wrote:My own personal observations have been curtailed since the Beast from the East, where the foodplant has really taken a battering and I wonder if this is limiting factor in the wild (i.e. a lack of nearby foodplant), rather that the ability of larvae to survive. Thoughts welcome.
Today the penultimate captive egg hatched here in Crawley. This particular one was laid at the Cemetery Wall site on 21st November 2017, which makes it 110 days old. The larva had chewed part of the top of the egg away during yesterday afternoon, and when I checked it again at 10.40 this morning, it was half way out of its egg.
One egg remains.
Vince