008 Caloptilia alchimiella

15.008 Caloptilia alchimiella (Oak Stilt)

ws: 10–13mm; May‐Jul; oak (Quercus spp); common in oak woodland throughout UK.

Caloptilia alchimiella §1 female

ID: Head smooth, hindtibia without bristles, midtibia thickened with projecting scales; S2 of labial palps not tufted; fw with median costal blotch; terminal cilia paler than ground colour; costal blotch yellow > C.alchimiella/robustella which are very similar. MBGBI2 gives a table of features for separating these two - features for alchimiella are given first:
Head - vertex purplish brown, darker than thorax (vs) vertex ochreous concolorous with thorax
Thorax - golden-yellow, tegulae pale purple brown (vs) ochreous, including tegulae
Forewing basal blotch - sharply defined (vs) diffuse
Forewing costal blotch - outer angle produced along costa almost to apex (vs) not or hardly produced along costa towards apex
Forewing tornal spot (yellow) - minute (vs) absent
Aedeagus - many small cornuti in two rows near base, single irregular row near apex (vs) 6-7 large cornuti in two rows
Ductus bursae - even width with evenly dispersed granulation (vs) narrows gradually towards bursa and abruptly towards ostium, granualtion strongest on one side at widest section of ductus.
Additionally C.robustella is rare outside SE England

Variation
Dissection
Male genitalia
Female genitalia

§1 Mull; 26/06/2011; female; fw 5.7mm
§2 Ardnamurchan, Highland; 14/07/2012; male
§3 Ardnamurchan, Highlands; 09/07/2012; male
§4 Orlestone Forest, Kent; 26/07/2018; male; fw 5.2mm
§5 Orlestone Forest, Kent; 18/05/2020
§6 Orlestone Forest, Kent; 24/06/2020; female; fw 5.6mm
§7 Foulness, Essex; 11/09/2021; male; fw 4.6mm
All images © Chris Lewis