Thursday, 7 March 2013

Morphology ...

CONCENTRATING ON THE DETAIL

Most identification of Lepidoptera does not require the use of a dichotomous key (a means for the identification of organisms based on a series of choices between alternative characters), but relies on pattern recognition and learning the species verbatim from images in books and the internet, the ability growing with experience. However, in most other large orders (e.g. Diptera, Coleoptera and Hymenoptera) even the beginner must learn from keys, or diagnostic characters to be able to distinguish taxa even at the family level. Although there are exceptions, it is generally not until the lepidopterist begins to tackle the microlepidoptera that the use of morphological characters (e.g. genitalia, wing venation and body structure) becomes commonplace, and often a prerequisite, in aiding identification.

Most butterflies and moths have two pairs of overlapping scaled wings. These are comprised of an extremely thin double membrane with rigidity provided by a network of nervures (the hollow ‘veins’ which radiate from the base of and form the framework of the insect’s wing). The pattern of nervures is different for each genus of butterfly and, as such, this is one of the key criteria used by taxonomists when classifying butterflies.

To venture a little deeper, the fore and hindwings of most moths, though not all, are united during flight by a coupling apparatus, the frenulum (a bristly structure on the hindwings that holds the forewings and hindwings together). This particular mechanism is never found in butterflies, in which the wings are held together only because the front pair overlaps the hind to a considerable extent. The amount of this overlap is increased by the humeral lobe, a special projection found only in butterflies, and situated at the basal end of the costa on the hindwings. This type of arrangement is known as amplexiform (clasp-like) wing-coupling.

The image below, of a female Brown Hairstreak (Thecla betulae), shows the humeral area, close to the rear and either side of the thorax. In addition, key wing venation is visible, including the radial and medial veins on the hindwing, and the radial, cubital and anal veins located on the forewing. The discoidal cell of the forewing is also clearly discernable.

A  Humeral area
B  Radial nervure (vein)
C  One of the medial nervules
D  Radial nervure (vein)
E  One of the cubital nervules
F  Cubital nervure (vein)
G  One of the anal nervures (veins)
H  Discoidal cell

I appreciate that this level of detail, which by no means is digging very deep, is not to everyone’s interest. However, for those who have the time and the inclination to do so, I thoroughly recommend looking a little closer and you will soon discover a whole new world full of fabulous hidden wonders …

Try it sometime ...

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