015 Swammerdamia caesiella

16.015 Swammerdamia caesiella (Birch Ermine)

ws: 9-13mm; bivoltine May-Jun, Aug; birch (Betula spp); common in heath and open woodland throughout GB

Swammerdamia caesiella §1

ID: keyed in MBGBI3 as - apex of forewing not orange (excludes Pseudoswammerdamia combinella); median fascia entire or obscure (not clear to me that this is sufficiently reliable to exclude Paraswammerdamia albicapitella which shows an interrupted median fascia); ground colour of forewing a shade of grey (not white, excludes S.passerella); terminal cilia not tinged coppery (excludes S.pyrella); tegulae fuscous and white, ws 14mm or less (excludes S.compunctella which is larger, ws 14-16mm and has even coloured tegulae; distinct white costal spot > S.caesiella (excludes Paraswammerdamia nebulella which shows 3-4 small clusters of white scales near costa before apex). Genital examination is probably required for confident identification.
Male genitalia: very long aedeagus.
Female genitalia: very long ductus bursae.

Variation
Dissection
Male genitalia
Female genitalia

§1 Kinlochleven, Argyll; 04/07/2011
§2 Kinlochleven, Argyll; 04/07/2011
§3 Kinlochleven, Argyll; 04/07/2011
§4 Kinlochleven, Argyll; 04/07/2011
§5 Kinlochleven, Argyll; 04/07/2011; female; fw 6.5mm
§6 Kinlochleven, Argyll; 04/07/2011; male; fw 5.5mm
§7 Winterton, Norfolk; 06/08/2015; male; fw 5.1mm; to light
§8 Chobham Common, Surrey; 23/05/2017; male; fw 5.2mm; to light
§9 Westcliff-on-sea, Essex; 02/08/2018; female; fw 4.8mm
§10 Loch Rannoch, Perthshire; 12/06/2021; male; fw 5.6mm
All images © Chris Lewis

Page published 30/01/2012 (§1-6) | §7 added 12/01/2016 | §8 added 11/12/2017 | §9 added 17/02/2019 | §10 added 14/09/2021