The saga continues: Entomology 101: Wing Structure and Wing Venation.
In the last section I introduced insect wings and will now move on to look at wing structure and venation. This post will confine itself to the essentials, with a more detailed look at variations in wing structure when I cover the insect orders in the chapter on diversity.
The wings connect to the thorax at three points, with various forms of axillae, which are stiff plates (sclerites) of cuticle that are activated by muscle movements in the thorax. Wings consist of two layers of cuticular membrane which sandwich a framework of veins through which hemolymph flows. The veins are also sclerotized and provide a strengthening structure to the wing. Other features of the wings include fold lines and lines of flexion. In some orders, the fore and hind wings move together as one when in flight, facilitated by various linking mechanisms.
Wing venation and the lines of folding and flexion all contribute to patterns that can assist in identification. The lines of venation have been ‘mapped’ with a common terminology called the Comstock-Needham system, which recognises the homology of wing veins across the insect orders. The Comstock–Needham system was developed by John Comstock and George Needham in 1898, and today it is variations of that system that are mostly used by entomologists. The Evolution of Insects goes with the Wootton variation (1979) which I follow below, while others may favour the Kukalova´-Peck variation.
Major veins are marked in upper-case letters with the branches indicated by numbers. Lower case letters indicate cross veins:
◊ The costa (C) is the vein that runs along the leading edge of the wing, and it stems from a small sclerite, called the humeral plate, at the wings base.
Immediately below the costa is the sub-costa (SC) which may branch (SC1 and SC2). The costa stems from the first axillary sclerite.
◊ The next vein is the radius (R) and its branches. The first branching branch(R2 to R5) that stems from R is sometimes labelled as the radial sector (Rs) in some diagrams. The base of the radius stems from the second axillary sclerite.
◊ The media vein (M) typically has two major branches, the media anterior (MA) and the media posterior (MP). The media stems from the distal end of the medial plate.
◊ The cubitus (Cu) is usually a three branched vein. The cubitus anterior (CuA) branches (CuA1 and CuA2), while the cubitus posterior (CuP) typically does not branch. The cubitus stems from the distal medial plate.
◊ The remaining veins are lumped together as the anal (A) veins, and they vary in number, and are also sometimes labeled anterior and posterior. The anal veins stem from the third axillary sclerite.
◊ The jugal region is found in some Lepidoptera and Trichoptera. It the posterior basal lobe, below the jugal fold.
The areas between veins are called cells, and naming system for these cells varies between insect orders. The only universal definitions are closed cell for those between veins, and open cell for those near the wing margin that have no confining vein.
Below is a diagram illustrating wing pteralia, showing the relative position of the different sclerites (in this case Diptera, the flies), and more…
Structure of the base of wing:
1: tegula or costal plate; 2: basicosta or humeral plate; 3: subcostal sclerite; 4: first axillary sclerite; 5: second axillary sclerite; 6: third axillary sclerite;7: stem vein; 8: proximal median plate; 9: distal median plate;
10: anterior notal wing process (mesonotum); 11: pleural wing process (mesopleuron); 12: posterior notal wing process (mesonotum);
13: costagial break; 14: humeral break; 15: lower calypter or squamula thoracica; 16: upper calypter or squamula; 17: alula or axillary lobe;
18: alular incision; 19 anal lobe;
A1: first anal vein; A2: second anal; C: costa; CuA: anterior branch of cubitus; CuP: posterior branch of cubitus; M: posterior branch of media; MA: anterior branch of media; R: radius; Sc: subcosta;
a1: anal cell; bc: basal costal cell; bm: basal medial cell; br: basal radial cell; c: costal cell; cup: posterior cubital cell; h: humeral crossvein.
As usual, if you see any errors, or if you have additional information, please comment below.
Next: Insect Legs
- Grimaldi, David and M.S. Engel, Evolution of the Insects, (pp. 128-130) Cambridge University 2005.
- Resh, Vincent H. and R. T. Cardé, Eds. Encyclopedia of Insects, (pp.1186-1192) Elsevier 2003.
- http://www.cals.ncsu.edu/course/ent425/library/tutorials/external_anatomy/wings.html http://roberto.kellerperez.com/wp-content/uploads/2009/11/lab10_11.pdf