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Clouded Knot-horn Homoeosoma nebulella

This species was previously assigned the vernacular name Large Clouded Knot-horn. This is a nationally scarce species but the records showing at Norfolk Moths suggest that it is reasonably common and very widespread in Norfolk. I am not sure how many of these records have been robustly confirmed though - I can't help wondering if some might be misidentified Phycitodes? Certainly I have not found it to be common - I'm yet to record it among nearly 1,000 species in my garden and never encountered it anywhere else until 2024.


This one was trapped in a meadow and was suspected as being nebullela from the off. In some ways it resembled a small and weakly-marked Phycitodes binaevella, but the spots on the wing were far too small (although I've caught several small binaevella before and a few with abnormally small spots, so you never know). With a forewing length of 10.5mm I couldn't rule out Phycitodes maritima but I've caught a few of them before and I didn't think this looked like one. However I needed to check the genitalia to be completely sure it was Homoeosoma not Phycitodes.

Although unlikely at this inland location I also needed to eliminate Sheep's-bit Knot-horn Homoeosoma nimbella and I am not aware of any differences in the genitalia of these two species. However like the Phycitodes species, nebulella has vein M2+3 in the forewing forked well away from the edge of the wing, according to the late Barry Goater's British Pyralid Moths (Harley Books, 1986). In nimbella vein M3 is either unforked or vein M2 forks off close to the edge of the wing (note veins M2 and M3 are sometimes referred to as vein 4 and vein 5). Goater says the wing venation is easily seen by examining the underside of the forewing, however this has not been my experience. In this case I could just about make it out, but not clearly enough to be 100% sure and certainly not clearly enough to show in a photo, so I rubbed a few scales off to reveal the venation a little more clearly. As it's still not enormously obvious in the photo (below) I've marked it with arrows to show the relevant points: the yellow arrow on the right shows where vein M3 emerges from the discal cell, the orange arrow in the middle shows where vein M2 forks off from vein M3 and the two red arrows on the left show the ends of veins M2 and M3.

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female Clouded Knot-horn Homoeosoma nebulella showing forewing venation and genitalia, Wendling Beck Environment Project (Norfolk, UK), 18th August 2024