Fairy Moth (Adelidae) probably Cauchas sedella - Cauchas sedella
6 miles NW Lyons, Boulder County, Colorado, USA
May 27, 2007
Size: FW ~ 4 mm
Male and Female found on the delicate spring mustard Fendler's Rockcress (Boechera fendleri -- Brassicaceae) in the CO foothills at ~6400'. These tiny Fairy Moths are in family Adelidae. Genus is almost certainly Cauchas based on description in Powell and Opler and BugGuide.
The list of Cauchas includes 6 species from North America. Two are described from Colorado, one from the mountains, C. cockerelli, and one from from Boulder, C. sedella. Based on the description, given below, this is almost certainly C. sedella.
Description from Busck, 1915, Proc. Ent. Soc. Wash. 17:93:
"Incurvaria [now Cauchas] sedella n. sp.
Labial palpi yellow with black terminal point and black setae. Antennae bronzy black with white tips. Face and head yellowish white. Thorax dark bronzy brown. Forewings dark bronzy brown with a white trans-
verse fascia at apical third; cilia ‘bronze. Hindwings dark purple with
basal half of costa silvery white; cilia dark golden purple. Abdomen dark
purplish brown. Legs silvery, shaded with dark purple. Alar expanse:
Habitat: Boulder, Colo., T. D. A. Cockerell, collector.
Type: Cat. No. 19289, U. S. N. M.
Taken by Prof. Cockerell on Sedum."
In this image, note the yellowish white face and head. Antennae with white tip. Wings with a white transverse band at apical third. Legs silvery, shaded with dark purple. Wingspread ~ 9 mm.
Incurvaria cockerelli is "larger, with darker head [face and head reddish ochreous] and yellow oval spot at apical third supplanting the white transverse fascia." Also, legs of C. cockerelli are dark bronzy brown.
In this image note that the male (upper) has larger eyes that the female, a characteristic of some members of this family.
Addendum: This moth is included in Opler's Moths of Rocky Mouontain NP list, April 23, 1998 version. It was described from Boulder. The location where we saw this moth is about halfway between these two sites.