The latest update from Michael Walter:
The world seems to be divided into those who luxuriate in this summer’s heat and those who find it unbearably debilitating. In the natural world there are also bound to be winners and losers: woodcock, which rely on probing soft ground for invertebrates, are probably suffering, but many young birds may have benefitted from the warm and dry conditions during the critical fledging period. We’ll have a better idea of the impact of this weather when we count the survivors next year. Insects in general, and butterflies in particular, are strongly associated with sunny conditions, so would be expected to be thriving now, but my weekly transects tell a remarkably different story. As the graph (right) shows, butterfly numbers closely followed the 39-year mean all through spring (Weeks 1-15), apart from a brief spike in week 10 caused by a flush of heath fritillaries, but in Week 16 (mid-July) fell off the proverbial cliff, never to recover. There are many possible reasons for this decline: if, as already mentioned, birds enjoyed a more successful breeding season, they, along with other predators, may have eaten more caterpillars than usual. The weather may also have boosted populations of insects that parasitize the larvae. Then again, most butterfly caterpillars feed on a fairly narrow range of plants, some of which are now wilting in the heat and therefore less nutritious. Two months ago I commented on drooping devil’s bit scabious; this made a fairly full recovery after welcome rain in July, but is once more looking half-dead. Next year could therefore see a depressed butterfly population or, conversely, if winter has been kind to them, numbers may bounce back to more normal levels. STOP PRESS: As I write on 15th August we have just experienced a tropical shower of 36mm, about 86% of a month’s expected rainfall!
On a blistering afternoon I was amazed at one spot in the wood to see water droplets glistening on the vegetation. Had the RSPB been spraying? This seemed unlikely, as bracken, oak seedlings and flowers alike were all coated, and only on one side of the ride. Then, when I touched the leaves, I realised that they were dry, and that I must be looking at desiccated honeydew, secreted by aphids high up in the canopy. These tiny insects spear the leaf tissue with their lance-like proboscis to feed on the sap, which bleeds out faster than the insects can cope with it, so much simply drops to the ground. Interestingly, the honeydew was all beneath a single oak; I couldn’t find any evidence of it elsewhere in the wood.
My sighting of a Jersey tiger (don’t panic - it’s a moth!) was a few hundred yards from the wood edge, but I can’t resist mentioning this very striking insect here. Originally a vagrant from Europe, it is now establishing itself along the south coast and in the London area. In flight its scarlet underwing flashes alluringly, but on landing the bright colour is tucked away beneath bold black and creamy striped upper wings, which break up its outline. The abrupt transformation from extrovert flasher to excellently camouflaged insect gives the impression of its having literally vanished into thin air.
Michael Walter
michaelwalter434@gmail.com
Oak leaves coated in shiny honeydew
Dead leaves still on a birch tree
Freshly shed alder leaves on 13th August