Diagnosis. The wing pattern resembles E. suberis and related species, but male E. heckfordi is separated from all except E. phaeolepis by the ochreous hairpencil on the hindwing base, which is surrounded by white androconial scales close to the hairpencil and brown scales along dorsum. The females lack the hairy abdominal tip of E. suberis and hendrikseni, but closely resemble E. andalusiae and phaeolepis, which are externally not separable. Male genitalia differ from suberis, andalusiae and hendrikseni by the very slight basal bump, which is much more distinct in the other species, whereas this bump is virtually absent in E. phaeolepis and caradjai. This and the next species differ from E. caradjai by the pointed gnathos (truncate in caradjai). Aedeagus at 360–400 μm distinctly longer than in E. phaeolepis and andalusiae (less than 350μm). In female genitalia hard to distinguish from E. andalusiae or E. phaeolepis, apart from slight statistical differences in numbers of setae on anal papillae and number of convolutions in ductus spermathecae (6 in andalusiae, 5.5 in heckfordi, 4.5 in phaeolepis).
Description. Male. Forewing length 2.2–2.7 mm (2.5 ± 0.2, 5), wingspan 4.8–5.8 mm. Head: frontal tuft yellowish white to ochreous, collar ditto; scape yellowish white; antenna brown grey, with 43–47 (44.2 ± 1.8, 5) segments. Thorax and forewings dark fuscous to black with paler scale bases giving some irroration; a straight dull white, medial fascia, usually wider at dorsum than costa; cilia-line more or less distinct; cilia ochreous grey; underside brown-grey, a narrow line of dark fuscous scales under costal fold near wing base. Hindwing and cilia grey, distinct field of androconial scales on basal half, reaching up to the dorsal margin, dark brown along dorsum, white near hairpencil, hair pencil ochreous; underside grey. Abdomen brownish black, with yellowish anal tufts.
Female. Forewing length 2.2–2.6 mm (6), wingspan 4.9–6.2 mm. Antenna with 30–34 (5) segments. As in male, but hindwing without androconial scales.
Male genitalia. Capsule length 250–265 μm. Vinculum distinctly concave anteriorly. Tegumen broadly rounded to almost truncate, without distinct processes or lobes caudally, with several long setae. Gnathos central element broadly triangular, lateral processes broad and rounded caudally. Valva length 185–210 μm, broad, inner margin with an indistinct basal bump, suddenly narrowed, not evenly curved; outer margin also slightly angled ca ¼ from tip, sublateral processes shorter than ½ transtilla length. Aedeagus 360–400 μm long, with distinct cathrema, with many very small cornuti in vesica, ventral pair of carinae simple, pointed.
Female genitalia. T8 with ca 14–17 setae on either side; T8 with rounded corners, and posteriorly straight. Papillae anales broadly rounded, with about 12–15 short setae each. Apophyses short and thick. Vestibulum with distinct vaginal sclerite and a “spiculate” pouch without spines. Corpus bursae ca. 560–600μm long, almost globular, covered with minute pectinations; signa almost similar, ca 330–370 μm long (n=2), approximately 1.9–2.1 as long as wide, ca 12 cells in width. Ductus spermathecae with about 5.5 sclerotized convolutions.
Hostplant. Reared from Quercus petraea (Matt.) Liebl.; in 2006 vacated mines were also found on Q. robur L.. Most mines were found on saplings, seedlings or low growth of Q. petraea and in the shade.
Leafmines. Egg on leaf underside, against leaf margin or a vein. Mine starts as a short, highly contorted gallery, occupying a small space only, filled with black frass, later broken; mine suddenly enlarged into an elongate blotch, with frass concentrated in two lines along the edges. Mine similar to that of other species in this group.
Larva. Distinctly green.
Life history. Larvae have been found from 2 August to early September and adults emerged indoors in April and May, certainly univoltine.