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Morphological Terms/Wings
Serna & Mackay (2010), Figure 46. Male wings. Veins: C: Costa, Sc+R: Subcostal+Radial, Sc+R1: Subcostal+Radial 1, R1: Radial 1, Rs: Radial Sectorial, 2r-rs: second radial-radiosectorial, M+Cu: Media+Cubital, M: Media, Rs+M: Radial sectorial+Media, 1 m-cu: first media-cubital, Cu: Cubital, cu-a: cubital-anal, A: Anal, rs-m+M: radial sectorial-media + Media. Cells: CC: Costal Cell, BC: Basal Cell (or Radial), SBC: Subbasal Cell (or Cubital), SMC1 + SMC2: Submarginal Cell 1 + Submarginal Cell 2, SMC3: Submarginal Cell 3, DC1: Discal Cell 1, DC2: Discal Cell 2; pst: pterostigma, tg: tegula.
Perfilieva (2011), Fig. 1. Nomenclature of veins and other structures of ant fore- and hindwings. Cell names are underlined; vein names, italicized. In vein notation, number in front of letter is serial number of vein segment from wing base; plus sign (“+”) indicates fused veins; subscript shows vein branch (e.g., R1 is anterior branch of radial vein). Dotted line shows position of functional folds and lines of wing flexion.
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Ala
Plural: alae
See Wings.
Cells of the wings
Sections of the venation of the wings surround areas of wing membrane that are called cells. The cells are purely a function of the veins that form their boundaries, and the shape and number of cells diminishes with the contraction or loss of various veins or parts of veins. Cells that are entirely surrounded by vein sections are termed closed cells, those in which one or more boundaries are missing are termed open cells. In ants that show the most complete venation there are nine closed cells in the forewing (10 if the pterostigma is included), and three in the hindwing, together with a number of cells in each wing that are always open, as defined below.
Unfortunately, there is no single agreed system for naming the cells, and several nomenclatures, some of them widely recognised but some idiosyncratic, are in use. The definitions outlined here indicate which sections of the venation form the boundaries of each cell, proximally, anteriorly, distally and posteriorly, so that the identities of individual cells can be correlated across the various systems. The names given to the cells here are in quite common use, but are by no means universal.
Cells of the forewing, named in alphabetical order.
- Basal cell [BC]. Bounded proximally by the wing base, anteriorly by Sc+R+Rs, distally by Rs·f1 and M·f1, posteriorly by M+Cu.
- Costal cell [CC]. Bounded proximally by the wing base, anteriorly by C, distally by Sc or the pterostigma, posteriorly by Sc+R+Rs and Sc+R.
- First Discal cell [DC1]. Bounded proximally by M·f1, anteriorly by Rs+M, distally by M·f2 and 1m-cu, posteriorly by Cu·f1 and Cu·f2.
- First Subdiscal cell [SDC1]. Bounded proximally by cu-a, anteriorly by Cu·f2, distally by Cu·f3 and Cu2, posteriorly by A·f2.
- First Submarginal cell [SMC1]. Bounded proximally by Rs·f1, anteriorly by Sc+R and R·f1, distally by 2r-rs, posteriorly by Rs+M and Rs·f2-3. Note that in the very few taxa where 1r-rs is present, SMC1 is divided into proximal and distal portions by this cross-vein. In this uncommon circumstance SMC1 (proximal) is bounded proximally by Rs·f1, anteriorly by Sc+R, distally by 1r-rs and posteriorly by Rs+M and Rs·f2. SMC1 (distal) is bounded proximally by 1r-rs, anteriorly by R·f1, distally by 2r-rs and posteriorly by Rs·f3.
- Marginal cell [MC]. Bounded proximally by 2r-rs, anteriorly by R·f2 and R·f3, distally by the junction of R·f3 and Rs·f5, or distally open when these veins fail to meet, posteriorly by Rs·f4-5.
- Second Discal cell [DC2]. Bounded proximally by 1m-cu and Cu·f3, anteriorly by M·f3-4, distally open, posteriorly by Cu1. In many aculeates there is an open third discal cell [DC3], but in ants this is never exhibited because cross-vein 2m-cu, which would form its proximal border, is universally absent.
- Second Subdiscal cell [SDC2]. Bounded proximally by Cu2, anteriorly by Cu1, distally open, posteriorly by A·f3.
- Second Submarginal cell [SMC2]. Bounded proximally by Rs·f2 and M·f2, anteriorly by Rs·f3-4, distally by 2rs-m, posteriorly by M·f3.
- Subbasal cell [SBC]. Bounded proximally by the wing base, anteriorly by M+Cu, distally by Cu·f1 and cu-a, or by cu-a alone when that vein is retracted, posteriorly by A·f1.
- Third Submarginal cell [SMC3]. Bounded proximally by 2rs-m, anteriorly by Rs·f5, distally open, posteriorly by M·f4. In many aculeates there is an open fourth submarginal cell [SMC4], but in ants this is never exhibited because cross-vein 3rs-m, which would form its proximal border, is universally absent.
Cells of the hindwing, named in alphabetical order.
- Basal cell [BC]. Bounded proximally by the wing base, anteriorly by Sc+R+Rs, distally by Rs·f1, 1rs-m, M·f1 and M+Cu, posteriorly by M+Cu.
- Costal cell [CC]. Bounded proximally by the wing base, anteriorly by C, distally by Sc+R, posteriorly by Sc+R+Rs.
- Discal cell [DC]. Bounded proximally by M·f1, anteriorly by M·f2, distally open, posteriorly by Cu.
- Marginal cell [MC]. Bounded proximally by Sc+R and Rs·f1, anteriorly by R, distally open, posteriorly by Rs·f2.
- Subbasal cell [SBC]. Bounded proximally by the wing base, anteriorly by M+Cu, distally by cu-a, posteriorly by A·f1.
- Subdiscal cell [SDC]. Bounded proximally by cu-a, anteriorly by M+Cu and Cu, distally open, posteriorly by A·f2.
- Submarginal cell [SMC]. Bounded proximally by 1rs-m, anteriorly by Rs·f2, distally open, posteriorly by M·f2.
See also Venation and Wings.
Clavus/Claval furrow
(Clavus = vannal lobe, = plical lobe/claval furrow = vannal fold)
See Wings.
Fenestra
Plural: fenestrae
In general, a thin spot or translucent spot anywhere in the cuticle. In the wing venation, fenestra is the name applied to a translucent spot or apparent break in a vein which indicates the point at which a flexion line or fold line traverses the vein. In the most generalised ant wings, such fenestrae occur in Rs·f2, 2rs-m, cu-a, and Cu2 of the forewing, and in 1rs-m and cu-a of the hindwing.
Flexion lines/folds
See Wings.
Hamuli
singluar: hamulus
See Wings.
Jugum
(= jugal lobe, = anal lobe)
See Wings.
Pterostigma
(= stigma)
A pigmented area that is usually present on the forewing of alate ants. When present it is located immediately behind the leading edge of the wing, about half to two-thirds of the distance from the wing base to its apex, and just distal of the hinge-like mechanism. It is bounded proximally and anteriorly by vein Sc, posteriorly and distally by vein R.
Radial flexion line
See Wings.
Remigium
See Wings.
Venation
(= neuration)
The configuration of the veins in the wings of ants, and other aculeates, is very much modified from the ancestral insect pattern. Within the Formicidae the venation is complex and extremely variable. There is a finely stepped series of reductions exhibited from a formicid ancestral common pattern, which is still represented in many subfamilies, in which the venation is most complete. In general, the venation of ants is very similar to that seen elsewhere in the vespoids, and also in the apoid lineages, but in ants the cross-veins 3rs-m and 2m-cu are always absent, and there is never a fenestra in M·f3.
There are a number of conventions useful in understanding venation and vein nomenclature.
- The leading edge of a wing when fully open, as if in flight, is its anterior margin; the trailing edge, in the same circumstances, is the posterior margin.
- The abbreviations of the names of the main, longitudinal, veins that run from the wing base (proximal) towards the apex (distal), are written with an initial capital letter, for example M (= media), Cu (= cubitus). These abbreviations of the names are usually reduced from their forms as expressed in the ancestral insect wing. This is purely for convenience and brevity; the main vein homologues, as they appear in the ancestral insect wing, are noted below.
- The abbreviations of names of the secondary veins (cross-veins), that extend between the main veins, are written in lower case throughout, for example 2r-rs, cu-a, always with the most anterior vein noted first.
- The plus sign (+) is used to indicate sections of veins that are indistinguishably fused together longitudinally, for example Rs+M. In fused veins the one that was ancestrally anterior, closest to the leading edge, is named first.
- The ampersand (&) can be used to indicate sections of separate veins that are fused end to end so that they appear as a single continuous vein. For example, the so-called stigmal vein, a hook-shaped vein that arises from the pterostigma in some groups, is actually composed of the second radial-radial sector cross-vein (2r-rs) fused to the fourth and fifth free abscissae of the radial sector vein (Rs); thus the stigmal vein is properly 2r-rs&Rs·f4-5. 2r-rs is written first because it is nearest to the anterior margin of the wing.
- Sections of main veins that occur between cross-veins, or between fused sections of main veins, are termed free abscissae and are represented ·f after the abbreviation of a main vein, then followed by a number; for example, M·f3 is the third free abscissa of the median vein (M). This convention is useful to indicate where sections of veins have been lost or are free from fusion with other veins.
The veins, taken in order of occurrence commencing with the anterior margin (leading edge), are as follows in the most complete venation pattern seen in ants.
Forewing longitudinal veins
- Costal vein (= Costa) [C]. Undivided, never fused with any other vein and sometimes absent.
- Subcostal vein (= Subcosta) [Sc]. In the proximal part of its length Sc is fused with R and Rs (Sc+R+Rs), which is almost always the thickest vein section in the wing. Beyond the point of divergence of Rs, Sc remains fused to R (Sc+R) until close to the base of the pterostigma where they divide, after which the apical portion of Sc extends along the anterior margin of the pterostigma and R along its posterior margin. In ancestral homology, the vein called Sc here is correctly Sc2, because in some Hymenoptera a more proximal Sc1 occurs that is absent in ants.
- Radial vein (= Radius) [R]. In its basal section fused to Sc and Rs (Sc+R+Rs), then continuing as Sc+R after the divergence of Rs. At the pterostigma Sc separates from R, which thereafter shows three free abscissae, R·f1–R·f3, of which R·f1 and R·f2 form the posterior margin of the pterostigma, and R·f3 extends along the leading edge of the wing distal of the pterostigma and termination of Sc. In ancestral homology, the vein called R here is correctly R1, because in many insect groups R branches into several veins towards its apex, R1, R2, R3, etc., of which R1 is the only remnant in Hymenoptera.
- Radial sector [Rs]. Proximally fused with Sc and R (Sc+R+Rs). Beyond its point of divergence Rs has a maximum of five free abscissae (Rs·f1–Rs·f5), and always has a section fused with M (Rs+M), which is present between Rs·f1 and Rs·f2. The latter, in more generalised forms, has a distinct fenestra, through which the radial flexion line passes. Rs·f5 may curve anteriorly to the leading edge, where it meets R·f3, but often it ends without reaching the margin. In its distant ancestry, Rs probably originated as a vein independent of R, but in all Hymenoptera, and almost all insects, R and Rs are fused basally. In ancestral homology, the vein called Rs here is correctly Rs1. In a very few Hymenoptera Rs branches in its distal half into Rs1 and a more posterior Rs2.
- Median vein (= Media) [M]. Basally fused with Cu (M+Cu), then with a free abscissa (M·f1) before its fused section with Rs (Rs+M). Distal of this, M has a maximum of three further free abscissae (M·f2-4). In ancestral homology the vein called M here is correctly MP (media posterior), the posterior member of two original median veins. The anterior median vein (MA, media anterior) has been lost in Hymenoptera and most other insects.
- Cubital vein (= Cubitus) [Cu]. Basally fused with M (M+Cu), then with a maximum of three free abscissae (Cu·f1-3) before branching, near the posterior wing margin, into Cu1 and Cu2. Cu2 sometimes anastomoses with the anal vein, but when free it has a fenestra, through which the claval furrow passes. In ancestral homology the vein called Cu here is correctly CuA (cubitus anterior), and its terminal branches are CuA1 and CuA2. This is because it is the anterior member of two original cubital veins, the posterior of which (CuP, cubitus posterior) has been lost in Hymenoptera.
- Anal vein [A]. A single unbranched, unfused vein that is closest to the posterior margin of the wing; with three free abscissae (A·f1-3) at maximum. In ancestral homology the vein called A here is most probably 1A. In some groups of Hymenoptera two, three, or rarely four, anal veins may be present (A1, A2, etc.).
Forewing cross-veins (a maximum of five)
- First radial-radial sector cross-vein [1r-rs]. Extremely rare in ants; when present it extends from R, close to the proximal end of the pterostigma, to Rs, where it marks the junction of Rs·f2 and Rs·f3. Because 1r-rs is only rarely present, this section of Rs is most often seen as Rs·f2-3.
- Second radial-radial sector cross-vein [2r-rs]. Extends from R at the base of the pterostigma (where it marks the junction of R·f1 and R·f2) to Rs, where it marks the junction of Rs·f3 and Rs·f4. In the most generalised ant venations 2r-rs is proximal of 2rs-m.
- Second radial sector-median cross-vein [2rs-m]. Extends from the junction of Rs·f4 and Rs·f5 to the junction of M·f3 and M·f4. In more generalised forms 2rs-m has a distinct fenestra, through which the radial flexion line passes. In the most generalised ant venations 2rs-m is distal of 2r-rs. The cross-vein 1rs-m is not attested in any Hymenoptera, having been obliterated by the proximal end of the fusion of Rs with M (Rs+M). A third radial sector-median cross-vein, 3rs-m, is never developed in Formicidae but is very common in other aculeates..
- First median-cubital cross-vein [1m-cu]. Extends from the junction of M·f2 and M·f3 to the junction of Cu·f2 and Cu·f3. A second median-cubital cross-vein, 2m-cu, is always absent in Formicidae, though common in apoids and other vespoids.
- Cubital-anal cross-vein [cu-a]. In forms with most generalised venation cu-a extends from the junction of Cu·f1 and Cu·f2 to the junction of A·f1 and A·f2. Extremely commonly, cu-a is retracted towards the wing base and arises from M+Cu. There is usually a fenestra in cu-a, through which the claval furrow passes.
Hindwing veins
These are basically the same as in the forwing, but somewhat simplified. For instance, the hindwing has no pterostigma and no section Rs+M, the main veins have fewer abscissae, the apical abscissa of Cu is simple, and there are no r-rs or m-cu cross-veins. As in the forewing, 1rs-m and cu-a have fenestrae. In a considerable number of ant taxa M·f2 has disappeared from the hindwing, so the apparently single vein that extends between Rs·f2 and Cu is actually 1rs-m&M·f1. See also Wings and Cells of the wings.
The minimal forewing venation observed in ants consists merely of a very faint remnant of Sc+R+Rs.
Wings
Singular: ala
(= alae)
Alate ants, winged queens and males, have two pairs of wings, as do all winged Hymenoptera. The forewings are largest and articulate with the mesothorax, where their extreme base is shielded by a tegula on each side. The hindwings are smaller and articulate with the metathorax. The forewing and hindwing on each side are held together by a series of small hooks, the hamuli (sing. hamulus), that arise from the leading edge of the hindwing and engage folds on the posterior margin of the forewing. This ensures that fore- and hindwing on each side beat as a single unit in flight. In ants the hamuli usually arise only from the hindwing vein R, but in a very few groups another patch of hamuli is present more basally, on vein C.
About two-thirds the way along the anterior forewing there is usually a pigmented patch, surrounded by veins, the pterostigma (= stigma), that is only very rarely absent. The main membranous area of each wing is the remigium, which contains the entire area between the leading edge and the claval furrow (= vannal fold), immediately anterior to vein A. Posterior to the claval furrow, on both forewing and hindwing, is a membranous area termed the clavus (= claval lobe, = vannal lobe, = plical lobe), which usually terminates in a slight claval notch (= preaxillary excision, = vannal notch) in the posterior wing margin. In some taxa, proximal of the clavus on the hindwing, is a separate lobe of membrane, the jugal lobe (= jugum, = anal lobe).
Within the membrane of the wings there are usually also two flexion lines or fold lines that allow the wing to flex during active flight. In the forewing the radial flexion line runs parallel with, and immediately posterior to, veins Sc+R+Rs and Sc+R. Towards its distal end the flexion line curves anteriorly towards the base of the pterostigma, where it is contiguous with the hinge-like mechanism, a weakened area at the pterostigmal base that allows the outer part of the forewing to deform during flight. From there the radial flexion line extends for a short distance posteriorly, then curves distally and extends outward towards the wing margin. In many groups the track of the radial flexion line is marked by a distinct fenestra in vein section Rs·f2 and in cross-vein 2rs-m. Just anterior to vein A, the most posterior longitudinal vein, is the claval furrow (= vannal fold). This passes through a fenestra in cross-vein cu-a and usually also a fenestra in vein Cu2.
The same flexion lines occur in the hindwing, but the radial flexion line is simpler. It runs longitudinally, posterior to Sc+R+Rs, often through a fenestra in cross-vein 1rs-m, then out toward the wing margin posterior to Rs·f2. The claval furrow runs just anterior to A, with a fenestra in cross-vein cu-a. In those taxa where the hindwing retains a jugal lobe, the lobe is separted from the clavus by the jugal fold, which in ants is often represented by a cleft in the membrane.
As well as these features, each wing usually bears a conspicuous series of longitudinal and transverse veins, collectively termed the venation, together with a series of cells, which are areas of membrane enclosed by particular veins or sections of veins. Both of these are discussed separately, see Venation and Cells of the wings.
References
- Cantone, S., Zuben, C.J. von. 2019. The hindwings of ants: A phylogenetic analysis. Psyche Article ID 7929717 (doi:10.1155/2019/7929717).
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