Caryocolum species generally have a similar wing patterning but vary, even within species, in the extent of darker markings. Where dark forms of any species are encountered it is unlikely that a determination can be made on forewing features alone. Caution should be applied particularly when attempting to identify specimens with any degree of wear and in many cases dissection is recommended - in all but one pair of species (alsinella/viscariella) the genitalia are distinctively different.
Comparison with C. alsinella
C. alsinella (wingspan 7.5 - 11mm) is usually significantly smaller than C. viscariella (10 - 14mm) but there can be a slight overlap, has more white scales in the centre of the forewing, lacks the small orange-ochreous patch in the basal area and the angulated fascia from costal to tornal spot is white (light yellowish-brown in C. viscariella). Although the genitalia are very similar the foodplant, distribution and habitat preferences may assist with the identification process.
Comparison with C. fraternella
C. fraternella is a fairly similar size (wingspan 9 - 13mm) and has a similar colouration but the dark bar from the costa to the fold is often lost in the general dark colouration extending along the costa. The warm yellow lower surface of segment two of the labial palps in C. fraternella is distinctive to that species in Britain; in C. viscariella it is yellowish-cream coloured below but heavily mottled with blackish brown.
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