Friday, 5 August 2016

Of Conopids and things

I was in Byfield yet again. And again I had some time to kill - about two hours in fact - so I ambled over to the pocket park, confident that yet again I'd find something of interest. In fact before I had even reached it I had cause to bring my camera into action. A couple of Lombardy Poplars stand at the northern edge of Byfield's playing field and some of the leaves bore reddish swellings.

Poplar leaf galled by the fly Contarinia petioli, Byfield.
4 August, 2016

To be more precise the swelling was near the leaf-stalk (the petiole) and was a gall caused by the fly, Contarinia petioli. This gall is widespread in England but little recorded; it often occurs on aspen too.

I must have taken this route over a hundred times and yet before me I suddenly found a fine plant of Angelica, Angelica sylvestris

Angelica beside the stream at Byfield. 4 August, 2016
It must surely only have established itself in the last year or so.The umbels of this plant attract large numbers of insects. but not today. After a moment of admiration, for it was a fine specimen, I moved on. 

We have about 24 species of Conopidae in the British Isles. These flies are slightly problematic in that dipterists are unsure about their relationship to other families. They may be related to the hoverflies and, like them, are often very good wasp mimics.  The commonest in my experience is Conops quadrifasciatus, and I was fortunate to find a pair in copula today on a knapweed plant.

A pair of Conops quadrifasciata in Byfield Pocket Park
This species is  very wasp-like but is known to be a parasite of the Red-tailed Bumblebee, Bombus lapidarius. The victim is pounced upon while in flight and the Conops lays eggs on the host's abdomen, prising apart the abdominal segments. These eggs hatch and the resultant larvae burrow into the bee and feed on the contents of the abdomen. Remarkably, if only one larva parasitizes the host, the bee may survive.

Several hazel, Corylus avellana, shrubs are present in the pocket park. One specimen has reddish foliage and may be the form known as 'Red Majestic'.

Red hazel at Byfield Pocket Park. 4 August, 2016
The nuts on this species are similarly reddish, as are the jagged involucres wrapped around the nut. In theory the hazels will be cut back almost to ground level (coppiced) on a regular cycle but this system may fall into abeyance. Our old friends Emma and Dave Marsh are on the point of leaving Byfield and they will be greatly missed. It is their sterling efforts that are responsible for the pocket park being kept in good order; its future maintenance is now uncertain and rampant growth is already obliterating some of the less-used paths. A few people gather the hazel nuts in a desultory manner but I prefer to leave them for the squirrels:

                            ...' neath the Hazel's leafy thatch,
                            On a stulp (sic) of mossy ground,
                            Little squirrels' gambols watch,
                            Dancing oak trees round and round.
                                                               Clare's Village Minstrel. 1821

Interesting to reflect that these would have been Red Squirrels. I wonder when the last were seen in Northamptonshire?

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