KEY to external features:
Stigmella species can be segregated into 3 reasonably discrete groups: those with a plain forewing, those with a pale postmedian fascia and no other markings, and those that do not fit into the former two groups. It is convenient to consider this last group first as they are relatively easy to identify and exclude.
Stigmella species can be segregated into 3 reasonably discrete groups: those with a plain forewing, those with a pale postmedian fascia and no other markings, and those that do not fit into the former two groups. It is convenient to consider this last group first as they are relatively easy to identify and exclude.
Group A)
Species that do not fit into Groups B or C
S.catharticella auromarginella trimaculella assimilella basiguttella pretiosa aeneofasciella
Species that do not fit into Groups B or C
S.catharticella auromarginella trimaculella assimilella basiguttella pretiosa aeneofasciella
Group B)
Species with a pale fascia but no additional pale spots
S.lapponica confusella betulicola sakhalinella luteella glutinosae alnetella microtheriella prunetorum aceris malella centifoliella ulmivora torminalis regiella crataegella hybnerella mespilicola floslactella carpinella tityrella salicis myrtillella obliquella sorbi plagicolella lemniscella
continuella aurella splendidissimella dryadella poterii filipendulae hemargyrella speciosa
(E.acetosae)
Species with a pale fascia but no additional pale spots
S.lapponica confusella betulicola sakhalinella luteella glutinosae alnetella microtheriella prunetorum aceris malella centifoliella ulmivora torminalis regiella crataegella hybnerella mespilicola floslactella carpinella tityrella salicis myrtillella obliquella sorbi plagicolella lemniscella
continuella aurella splendidissimella dryadella poterii filipendulae hemargyrella speciosa
(E.acetosae)
Group C)
Species with a plain forewing
S. tiliae anomalella spinosissimae viscerella paradoxa magdalenae nylandriella oxyacanthella pyri minisculella desperatella zelleriella incognitella perpygmaeella suberivora svenssoni ruficapitella atricapitella samiatella roborella
Species with a plain forewing
S. tiliae anomalella spinosissimae viscerella paradoxa magdalenae nylandriella oxyacanthella pyri minisculella desperatella zelleriella incognitella perpygmaeella suberivora svenssoni ruficapitella atricapitella samiatella roborella
Where genital dissection is required to distinguish a species pair of group the distinctions are addressed on a separate (linked) page
In identifying adults of genus Stigmella the following features should be noted:
- Presence, position, shape, colour, metallic-ness/shininess of distal pale fascia
- Presence and position of any other pale spots
- Colour contrast between apex of forewing and terminal cilia
- Colour of frons, vertex, collar and eye-caps (scape)
- Antennal length relative to forewing length; colour contrast in the flagellum
- Forewing colour pattern and presence of additional fascia or spots
- Presence, shape and distribution of any hindwing androconial scales (males only)
- Presence, colour and extent of anal tufts
- (Wingspan / forewing length are seldom of value in identification as all Stigmella are small there is considerable overlap of size ranges)
Distal forewing fascia
Most fascial features are constant within a species and vary between the species. In Stigmella the fascia is nearly always postmedian but the exact position varies between the species. The fascia may be transverse or slightly to distinctly oblique; it may be of constant width, relatively narrow or broad; it may be constricted in the middle, sometimes sufficiently to be divided into costal and tornal spots and the degree of constriction may vary within a species; it may taper, when it does it is usually broader at the dorsum. The colour is always paler than the remainder of the forewing and ranges from white, silver, gold to grey. It is usually discrete and contrasts strongly with the rest of the forewing, but in a few species it may be obscure or have diffuse margins and in S.aceris it ranges from distinct through obscure to absent. The fascia may be distinctly metallic, shiny or dull.
Most fascial features are constant within a species and vary between the species. In Stigmella the fascia is nearly always postmedian but the exact position varies between the species. The fascia may be transverse or slightly to distinctly oblique; it may be of constant width, relatively narrow or broad; it may be constricted in the middle, sometimes sufficiently to be divided into costal and tornal spots and the degree of constriction may vary within a species; it may taper, when it does it is usually broader at the dorsum. The colour is always paler than the remainder of the forewing and ranges from white, silver, gold to grey. It is usually discrete and contrasts strongly with the rest of the forewing, but in a few species it may be obscure or have diffuse margins and in S.aceris it ranges from distinct through obscure to absent. The fascia may be distinctly metallic, shiny or dull.
Terminal cilia
The degree of contrast between colour of the apex of the forewing (invariably dark) and the colour of the terminal cilia ranges from very distinct to concolorous. The termen may have a line of dark-tipped scales and the cilia distinctly contrastingly white; the cilia may be less contrasting but still noticeably paler than the forewing apex or they may just have a subtly different colour. There may be a line of contrast within the cilia - always with the apex paler than the base.
The degree of contrast between colour of the apex of the forewing (invariably dark) and the colour of the terminal cilia ranges from very distinct to concolorous. The termen may have a line of dark-tipped scales and the cilia distinctly contrastingly white; the cilia may be less contrasting but still noticeably paler than the forewing apex or they may just have a subtly different colour. There may be a line of contrast within the cilia - always with the apex paler than the base.
Colour of frons, vertex, collar and eye-caps
The eye-caps are always white or whitish, sometimes with hints of yellow, gold or ochreous. In a few species they have a darker margin (betulicola, alnetella, lemniscella). The frons and vertex are usually concolorous but in a few species there is a colour contrast between frons and vertex. Head colour can be quite variable within a species and some species are sexually dimorphic for this feature. Collar colour is more constant but can be variable in some species and a few species are sexually dimorphic for this feature. (It can therefore problematic to use these features in devising a key)
The eye-caps are always white or whitish, sometimes with hints of yellow, gold or ochreous. In a few species they have a darker margin (betulicola, alnetella, lemniscella). The frons and vertex are usually concolorous but in a few species there is a colour contrast between frons and vertex. Head colour can be quite variable within a species and some species are sexually dimorphic for this feature. Collar colour is more constant but can be variable in some species and a few species are sexually dimorphic for this feature. (It can therefore problematic to use these features in devising a key)
Antenna
Male antennal length ranges from just <½ to ¾ forewing length. The male antenna is almost invariably longer than the female of the same species and female antennal length rarely exceeds ½ forewing length. Number of antennal segments shows considerable intraspecific variation, but differences in range may help to identify a few species. S.ulmivora is distinct in having the apical ¼ contrastingly whitish; S.tityrella has the apical ~⅓ contrastingly dark.
Male antennal length ranges from just <½ to ¾ forewing length. The male antenna is almost invariably longer than the female of the same species and female antennal length rarely exceeds ½ forewing length. Number of antennal segments shows considerable intraspecific variation, but differences in range may help to identify a few species. S.ulmivora is distinct in having the apical ¼ contrastingly whitish; S.tityrella has the apical ~⅓ contrastingly dark.
Forewing colour
In species with a fascia the apical area distal to the fascia is almost invariably darker than the area proximal to the fascia. Exact colours can be difficult to determine accurately in shiny metallic species especially in images taken with flash photography, but colour contrasts can be determined with greater confidence. I have found this a major problem particularly when photographing live moths. -without flash it is not possible to get sufficient depth of field for an optimally in-focus image. Two species have a less well-defined less contrasting proximal fascia in addition to the distal pale fascia (pretiosa, aeneofasciella). S.auromarginella has a pale gold scale patch at the extreme apex. 2 species have a distinct pale spot in the basal ⅓ with the distal fascia divided into costal and dorsal spots (trimaculella, assimilella) and S.basigutella usually has a pale basal spot and no distal pale fascia. S.catharticella has a white tornal spot and no other pale markings
In species with a fascia the apical area distal to the fascia is almost invariably darker than the area proximal to the fascia. Exact colours can be difficult to determine accurately in shiny metallic species especially in images taken with flash photography, but colour contrasts can be determined with greater confidence. I have found this a major problem particularly when photographing live moths. -without flash it is not possible to get sufficient depth of field for an optimally in-focus image. Two species have a less well-defined less contrasting proximal fascia in addition to the distal pale fascia (pretiosa, aeneofasciella). S.auromarginella has a pale gold scale patch at the extreme apex. 2 species have a distinct pale spot in the basal ⅓ with the distal fascia divided into costal and dorsal spots (trimaculella, assimilella) and S.basigutella usually has a pale basal spot and no distal pale fascia. S.catharticella has a white tornal spot and no other pale markings
