Another fine day on Salisbury Plain on Thursday with Dave Gibbs. Added a few more scarce insects to our list from the first visit, including the red-tailed cuckoo-bee Bombus rupestris, and the weevil Protapion filirostre (a new beetle for me). The suction sampler also turned up another individual of Ptomaphagus varicornis, the Red Data Book beetle I recorded here on 11th May, and this time I was able to show it to Dave in the field. With Knapweed Broomrapes pushing skywards, Small Blues on the wing, and a Quail quick-lick-licking from a nearby field, it reminded me of a few happy weeks surveying invertebrates on Salisbury Plain in 1997, my first job after finishing my PhD.
A surprise record from 11th May was a single individual of Rhinusa collina, a weevil which develops on Common Toadflax Linaria vulgaris. This is a Nationally Scarce (Na) species with a single previous Wiltshire record. I hadn’t even noticed any Linaria on 11th May but on Thursday, we made a specific search for the plant and eventually found a small patch of a few sprigs up to about 5 inches high within an area of about two square feet. The first sprig I looked at had four elongate cylindrical weevils on it of a species I’d never seen before! My first thought was Baris but I soon found a match in Mecinus janthinus, Nationally Scarce (Na) and another one new to Wiltshire. I suction sampled the entire population of the host plant, which only took a few seconds, and produced one more Mecinus janthinus, three Rhinusa collina, two Rhinusa linariae (Nationally Scarce (Na); one previous Wiltshire record) and the pollen beetle Brachypterolus linariae.
I don’t know whether anyone else has come to the same conclusion but I think the way to find both the two scarce Rhinusa species is to look at Linaria when it is just a mere few inches high. By the time it is in flower, all I ever find is the common one, Rhinusa antirrhini. My dates for the three species are as follows:
- linariae (Na) 17th May to 5th June
- collina (Na) 31st May to 2nd June
- antirrhini (Common) 9th July to 14th September
So if anyone is out and about now and sees Linaria, it would be interesting to know which weevils you find. As Thursday’s observations show, even a tiny patch of the plant can support the scarce species.
The suction sampler is turning up a lot of interesting beetles for me but, unexpectedly, the flies in the suction samples have been very interesting too. There are a few species with very reduced wings that are clearly adapted to a life on foot. But there are also some species which look perfectly capable of flying off but choose a ground-hugging way of life, running about in the bottom of the tray and seeming reluctant to even climb up the walls to escape. Amongst Thursday’s samples Dave has already identified two Nationally Scarce species, Geomyza apicalis and Geomyza breviseta, with more specimens still to be looked at. I guess these flies would be recorded more often if more dipterists used suction samplers – they’re probably not so scarce, just very good at eluding capture by nets!