November is a key month in the Emperoring calendar. It presents one of the best opportunities for finding this elusive and evasive insect - through something barking mad called Dangle Leafing.
In mid or late autumn, Emperor caterpillars gradually change colour, from Lincoln green to drab greys or browns. They then quit their feeding leaves, and wander off to hibernate, mainly by buds or in forks.
Crucially, all through their development the larvae tie their feeding leaves on to the branch with silk, assiduously so in autumn. The inevitable then happens: the leaf petiole join breaks, but the silk holds the vacated, withering leaf - dangling gently, until wind, rain or time break the silk.
Often, there is just a lone, brown leaf dangling, like this -
Occasionally, whole clusters can be found, like this -
These clusters are near-diagnostic, as other Lepidopteron larvae very rarely produce dangles (but, as it sayeth in the good book, 'Beware of false prophets, many will come in my name...'.)
Anyone who spent their youth fishing will take readily to dangle leafing. It's a bit like fly fishing on a chalk stream: plenty of systematic wandering, constant vigilance, looking for spinning leaves; the last thing you do is cast. Then, using a shepherd's crook or just scanning with binoculars, look for the hibernating larva - if you're lucky, it will be within half a metre of the dangle; if you're unlucky it will have gone walkabout big time.
But, there are good Dangle Leaf localities - notably, sheltered woods with small-leaved or narrow-leaved sallows, especially sallows in the lea of conifer blocks or in stream gullies - and there are poor Dangle Leaf localities, notably open woodland where there are tall broad-leaved sallows, whose dangles readily blow off.
And there are good Dangle Leaf autumns, and bad Dangle Leaf autumns - depending largely on wind and rain. And, crucially, there are Early, Mainstream and Late leaf-fall sallows.
This autumn, Dangle Leafing is not proceeding at all well, at least not yet. We suspect that the heatwaves caused a lot of early instar dangles (created by first and second instar larvae) to fall early. Also, Storms Austen and Boelo stripped a lot of dangles prematurely.
Also, in the absence of frost, many sallows are staying green long into autumn. Indeed, at this rate the broad-leaved sallows may not produce dangles until December.
Dangle Leafing really requires a series of visits, over a three week period. It is rather hit and miss. On a good day you can find half a dozen larvae, especially in good light.
But give it a go, most are found between 3-5m up.
And as for the Savernake final instar larva, it was still there on Nov 8th, fully grown and bright green. Only there are now two of them...
Remember, a butterfly is only a caterpillar partying...
