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I haven't a key so could someone please tell me the main differences between the two UK species?
Is there a size difference?
Can I assume that the humeri of nagatomii are orange? And what are the 'posterior calli'?
Apart from the amount of orange on the tergites, are there any other differences, perhaps between males and females?
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The posterior calli are the small 'humps' at the rear of the thorax, next to the corners of the scutellum. Basically, the hind corners of the thorax.
nagatomii...frons metallic green. Humeri and posterior calli bright yellow. Tergites bright yellow with at most small black markings.
tibialis...Humeri normally partly dark and posterior calli dark brownish or drab yellow. Abdomen often extensively dark, but in females with large pale areas; the yellow is dull rather than bright.
Further details of nagatomii...first tergite of both sexes and and last tergite of male are mainly or entirely black. Body length 6-7mm; wing 5mm.
Further details of tibialis...The abdomen is drab, in the male having only small pale orange patches at the front of tergites 2, 3 and 4, while in the female the central orange area of tergites 2-5 amounts to only about half their total width (in nagatomii the black lateral markings are reduced to small triangles, while tergites 7 and 8 are usually entirely orange) Body length 7mm; wing 4-5mm
All details from Stubbs and Drake
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thanks a lot for that, Ian. It sounds like a question of what's bright or dull yellow then, unless comparing the tergites is enough. Perhaps fairly obvious with a specimen of each side by side
The difference seems to be pretty obvious when you have them in front of you. I only have one pair of nagatomii, but they are very bright compared to tibialis, with the humeri and posterior calli very bright, whereas the paleness of those features is not at all obvious in tibialis. nagatomii has the spines on the scutellum bright yellow, too, on mine. The difference in colour of the humeri is far more obvious in these than in the hovers Sphegina clunipes and elegans, say, where the colour of the humeri is used as a feature.
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