Wednesday, 15 July 2015

Hogweed and Hoverflies

I snatched about half an hour today to take a look at Byfield Pocket Park. It had rained heavily on and off for three days but the ground had generally drained well.

Elm leaf with a gall caused by an aphid, Eriosome ulmi.
Byfield, Northants. 15 July, 2015
On the way I passed some elm (and very painful it was too) and noted that the leaf edges were rolled in a sausage-like manner. This is the work of the Elm-currant Aphid, Eriosome ulmi. I was rather pleased for, though I suspect it is widespread, the NBN Gateway map for this species shows no records at all for the English midlands. Quite a few leaves were affected.
Chromatomyia 'atricornis' is probably responsible for
this mine on Smooth Sow-thistle.  Byfield. 15 July, 2015

After this interesting record, and only a few feet away, came the far more mundane Chromatomyia 'atricornis'. The specific name is in inverted commas as there is some doubt about the precise species involved. It was in the form of a mine on Smooth Sow-thistle.

Approaching the pocket park I saw that Hogweed, Heracleum sphondylium, was in bloom.

The broad, flat umbels of this member of the carrot family stood out well against a backdrop of Rose-bay Willow Herb, Chamaenerion angustifolium, whilst in the foreground Perforate St John's Wort, Hypericum perfoliatum, flourished. The government has announced a new housing policy designed to utilise these brownfield sites (the pocket park stands where on land once occupied by Byfield railway station), but many are - clearly - very rich in wildlife.

Perforate St John's Wort. Byfield Pocket Park, Northants.
15 July, 2015

The hogweed was attracting many insects with beetles and two-winged flies prominent. Among the latter were great number of hoverflies. 

Episyrphus balteatus on hogweed.  Byfield Pocket Park,
Northants. 15 July, 2015

Some 90% of these were so-called Marmalade Flies, Episyrphus balteatus. These are familiar to most people and, as a child, I assumed they were a kind of small wasp. The word balteatus means belted or girdled and our word 'belt' comes from the same origin.

Myathropa florea. Byfield Pocket Park
15 July, 2015

Another hoverfly, Myathropa florea, was frequent. There is a distinct loop in the wing veins and, crucially, a pair of pale marks on the thorax, i.e. a little behind the head. It is clearly another wasp mimic.
Syrphus ribesii on hogweed. Byfield Pocket Park,,
Northants.  15 July, 2015

A third hoverfly was Syphus ribesii. It is extremely common and is one of the first of this family to be encountered by the newcomer. In their ground-breaking book 'British Hoverflies' the authors, Alan Stubbs and Steven Falk, state that 'the noticeable hum that emanates from tree canopies in woodland during summer seems mostly attributable to the they rest in foliage with their wings vibrating at high frequency'. The example photographed is a male.

Eristalis arbustorum. Byfield. 15 July, 2015

And here is another male, this time Eristalis arbustorum. It is one of our commonest hoverflies, frequent even in small gardens. It is one of those species whose larvae are known as rat-tailed maggots, found in organically-rich ponds and ditches.

The muscid fly,  Graphomyia maculata at Byfield
Pocket Park.  15 July, 2015
Of course, many other flies other than hoverflies were enjoying the double bounty of nectar and pollen. One of the most distinctive is Graphomyia maculata. It is one of the Muscidae and is thus related to the common house-fly. Although it is quite unmistakable it is amazing how may photographs of this on Google are in fact different species, often not even in the same family.

Fresh young leaves produced by an oak, an example
of Lammas growth. Byfield Pocket Park. 15 July, 2015

A fine oak was adjacent to the hogweed and was exhibiting Lammas growth. Lammas, traditionally on 1st August, was a feast-day celebrating the first fruits of the harvest. Lammas growth on trees is a familiar sight to anyone who strolls through woodlands but generally occurs in early July. Perhaps climate-warming is bringing it forward?

As I said in the opening paragraph I only had half an hour in the pocket park and I could have done with more time examining this oak, checking it particularly for small bugs, but it was not to be. 

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