As well as the handsome insects, a migrating Tree Pipit called from the wood near the Picnic Meadow. These once common birds are now scarce on farmland and have disappeared from London as breeding birds, but still drop in occasionally in spring and autumn migrations, and breed on larger commons such as at Thursley.
Suddenly it’s actually hot in the nature reserve.
The wildflower meadow in front of the hut shimmered in the sunshine, with bumblebees buzzing around the many Red Campion flowers. A Brimstone visited, for once perching quietly to drink nectar from the flowers. A large brown Shield Bug flew in and clambered up a twig in the hedge. A Red Admiral flew over too. We spent the morning making pegs – like overgrown foot-long sharpened pencils – to fix down the long thin logs we’re using as path edgings. It was pleasant working as a team, with cutting to length and then sharpening with the billhook going on simultaneously.
In the woodland where little shafts of sunlight reached the understory, Speckled Woods danced about or perched.
Down at the pond, Azure Blues (the ones with the little drinking-cup mark at the base of their abdomens) darted about, chasing each other off perches and flying in cop with what seemed to be rather few females compared to the number of eager males. A smaller number of Large Red Damselflies similarly chased and mated.
The “Mangrove Swamp” has lost almost all its standing water now: last week it had risen after being very low, but it only takes a few days for the level to fall dramatically. The frog tadpoles in the last pool were wriggling in a few centimetres of muddy water. I scooped them up in a bucket and popped them into the pond, where they’ll have to take their chances with the ducks alongside the toad tadpoles. The toad-poles may be somewhat distasteful like the adults, so perhaps the frog tadpoles are more palatable?
The Yellow Irises on the pond are starting to suffer from Iris Sawfly, a few of the leaves showing many small bite-marks along their margins.
A small diving beetle obligingly came to the surface to replenish its air supply, staying up there for a minute and then zooming down to the bottom when I came close.
Well, I usually try to take a pretty picture to start off a posting, but this one certainly doesn’t qualify. These leaf miners grow entirely inside a leaf, in this case of Spinach Beet. As you can see, as they grow they tunnel around below the leaf’s upper epidermis, which is a translucent layer of cells, leaving it intact to provide themselves with a ready-made cover.
Underneath that sheet, a healthy leaf contains a thick green set of palisade cells in one or several layers. These are the leaf’s (and the plant’s) factory, as they are full of chloroplasts, coloured green to absorb light: they synthesize the sugars on which life depends.
Not many people would want to eat this leaf, once the leaf miner larvae – mostly moths – have been at work. The palisade layers are entirely and efficiently destroyed wherever the insects have been. All that remains is an air-space and some dark frass: all, that is, but for the plump whitish cylindrical bodies of the larvae themselves.
Also nesting on the spinach are some ladybirds. These have incomplete metamorphosis, the young being able to walk as well as eat from their first stage or instar. Each time they moult they change in appearance as well as in size. They mainly eat aphids, troublesome pests of many crops, so they are useful to gardeners and to any farmers who don’t want to use insecticides.
This shield bug, seen here in close-up, may look conspicuous enough, but that is the camera’s view. The insect is actually rather well camouflaged, and it generally hides under a leaf where it is in some shadow. The camouflage consists first of a general colour resemblance to its background, with its overall grass-green coloration; and as seen here, it is also disruptively patterned, with the reddish brown of its wings tending to break up its outline. Perhaps it is also somewhat countershaded, with dots stippling its back. Bugs suck plant juices, and their larvae can be quite destructive, but they never seem to do much harm to the spinach.
There are also some green caterpillars, excellently camouflaged with a pale cream stripe all along their sides. (It might be the Hebrew Character moth.) You might expect this to be conspicuous, but it seems to be a classic piece of disruptive coloration: the stripe appears like a sun-glint specular highlight on the shiny crumpled surface of the spinach leaf, rather than part of a solid, round-bodied animal.
A pest I know is there is the Gooseberry Sawfly. There are numerous sawflies in the garden right now, but they are all flying around the Nasturtiums, nowhere near the gooseberry bush. However… plenty of the lower leaves of the gooseberry are badly damaged by sawfly larvae, some eaten right down to the petiole, pathetic little stumps with a few short branching veins all that remains of once green foliage. What to do about it? This isn’t a how-to-garden site, but inspect your gooseberry bush(es) regularly, looking especially at the lower leaves to see if they’re being eaten. If some are, check the edges for caterpillars. If you find any, spray the bush after sunset on a dry still evening (to avoid killing the bees that are pollinating your fruit) with a garden insecticide.
Five minutes of careful searching of half-eaten gooseberry leaves failed to reveal a single larva. The cause in this case is not so much camouflage as the incredibly intense predation by Blue Tits (and Great Tits). I estimate these little birds are a hundred times better at finding caterpillars than I am. They have the advantage of getting in close – they must be able to focus down to a few centimetres, their small eyes acting as short-focus wide-angle lenses – and of being able to perch anywhere in a bush. They also get up very early, and know instinctively exactly what food looks like: small well-camouflaged caterpillars on the undersides and edges of leaves.
Zoologists suppose that birds have a ‘search image’ of the prey they are hunting: perhaps this is much the same idea as the training images that computer scientists use to teach their neural nets to recognise patterns such as faces. Once you have such an image in your brain, you almost instantly recognise your target when it appears. To give a small illustration, I remember when I had a small motorbike, I always saw bike shops everywhere; now I never notice them. My eye was attuned, like a Blue Tit’s to a caterpillar.
Further to the World on a Blackcurrant Leaf, today the Ichneumons and the Harlequins were joined by two more conspicuous flying visitors, some green Shield Bugs (true bugs, Hemiptera) and some swift yellow-abdomened Sawflies, most probably Gooseberry Sawfly. Both of these are held in definite disfavour by many gardeners, the bugs for sucking plant juices and possibly weakening plants or spreading disease, and the sawflies for making caterpillars which in a bad year can totally defoliate gooseberry bushes — it only happened to me once, and it was quite a shock: from seeing the first little green caterpillars to leafless plants only took a week or so.
Since then I have carefully checked the gooseberry every few days for signs of sawfly damage (and actual caterpillars). If there are just a few, I remove the affected leaves and squash any caterpillars I find; this usually does the trick. If there are many, which has only happened once or twice, I consider spraying, choosing a time without wind, after sunset so the bees aren’t flying, and work close to the bush to keep the stuff local. The approach seems to work well for bees and berries.
As for the bugs, well, I rather like their handsome appearance and their confident swagger. There always seem to be enough currants so I don’t mind if the yield is down a bit on what it might have been.