After a day and a half of sometimes torrential rain, the sun came out briefly late afternoon and we walked round the garden. Hanging on a strong but delicate thread of silk was this bright green caterpillar. I had trouble working out whether it was a Hawthorn Sawfly or a Green Oak Tartrix Moth caterpillar, both of which will fall while spinning a line of silk from their host trees, either to escape a predator or when dislodged by strong winds or rain. We watched this one slowly and painstakingly climb back up its thread, still being blown around in the wind, till it arrived on a Hawthorn leaf, which made me wonder about it being the Hawthorn Sawfly but if you look carefully there is another part of the thread leading up, and what is above the hawthorn is an oak tree! Also, Sawflies have more continuous legs down their body while caterpillars have pairs near the head and towards the tail, which, on downloading, this one looks to have. The Green Oak Tartrix caterpillar has a narrow time margin to survive- the eggs, laid near leaf-buds, have to hatch just as the new leaves emerge- before and they starve, later and the tannins building in the leaves are indigestible to it. Sometimes there are so many caterpillars they completely defoliate an oak tree!
Timing is also vital for their predators, especially Blue Tits as these caterpillars form the staple food of Blue Tit nestlings. After feeding up, the caterpillars roll themselves in an oak leaf, sealing it with silk, and pupate.
Conditions: Rain and more rain till late afternoon. Temperature: Max 17- Min 9 c.