Morphological Measurements

Size and shape characters are quantified and reported as lengths or indices. Measurements are normally recorded in thousandths of a millimetre but reported to the nearest hundredth as a range from minimum to maximum across all measured specimens.

Within ants there are a "core" set of measurements and indices that are used across most groups. In addition there are specialised measures for structures and features that are only found in certain taxonomic groups. These are listed separately below.

Core Measurements

 * EL: Eye length measured in one of two ways: (1) Maximum eye length measured along the maximum diameter or (2) maximum eye length measured in full face view.
 * EW: Measured one of two ways:
 * Maximum eye width.
 * Maximum eye width measured in full face view.
 * HL: The length of the head capsule excluding the mandibles, measured in full face view in a straight line from the mid-point of the anterior clypeal margin to the mid-point of the posterior margin. In species where one or both of these margins is concave the measurement is taken from the mid-point of a transverse line that spans the apices of the projecting portions.
 * HW: The maximum width of the head in full face view, excluding the eyes. (Maximum width is usually posterior to level of eyes. Lateral tubercles and projections are generally ignored.)
 * MandL. The straight line length of the mandible at full closure, measured in the same plane for which the HL measurement is taken (i.e. full face view), from the mandibular apex to the anterior clypeal margin, or to the transverse line connecting the anterior-most points in those taxa where the margin is concave medially.
 * ML (Mesosomal or Weber's length). The diagonal length of the mesosoma in profile from the point at which the pronotum meets the cervical shield to the posterior basal angle of the metapleuron.
 * Note that often the posterior point of measurement for ML is the propodeal lobes rather than the metapleuron.
 * PronW. The maximum width of the pronotum in dorsal view. (Projecting spines, tubercles or other cuticular prominences at the pronotal humeral angles are ignored.)
 * SL: The maximum straight-line length of the scape, excluding the basal constriction or neck that occurs just distal of the condylar bulb. (In taxa with a hypertrophied subbasal lobe on the scape SL is measured from the tip of the subbasal lobe to the scape apex.)

Core Indices
Note that in about 70% of cases indices are multiplied by 100 (giving a range of 0-100) rather than being expressed as simple ratios (with a range of 0-1).
 * CI (cephalic index): HW/HL x 100.
 * Eye size indices:
 * EI (eye index): EL/HW x 100.
 * REL (relative eye length) EL/HW x 100.
 * MandI. MandL/HL x 100.
 * SI (scape index): SL/HW x 100.

Specialised Measurements

 * Antennal segment measurements:
 * A11L, A10L, A09L, A08L: length of 11th to 8th antennal segment.
 * A11W, A10W, A09W, A08W: width of 11th to 8th antennal segment.
 * CFW: Clypeal fork width measured between the anterior-most points of the clypeal teeth.
 * HFL: Maximum length of hind femur, measured in anterior view.
 * HTL: Maximum length of hind tibia, excluding the proximal part of the articulation which is received into the distal end of the hind femur.
 * MTL: Maximum length of mid tibia, excluding the proximal part of the articulation which is received into the distal end of the femur.
 * PetH: Petiolar height in lateral profile measured as the perpendicular distance from the ventral margin to the highest point of posterolateral tubercles; if ventral margin is concave upward then measured from a line tangent to the uppermost portion of the curve and oriented as close as possible to the long axis of petiole.
 * PetI (petiolar index): PetW/PetL x 100.
 * PetL: Measured one of two ways:
 * Maximum length of the petiolar node in dorsal view.
 * When viewed in lateral profile and measured in the same plane as the anterodorsal face, the distance from the inflection point marking the juncture of the posterolateral lobes and the cylindrical posterior portion of the segment to the anterior inflection point where the petiole curves up to the condyle or, if the inflection point is not visible, where the petiole is obscured by the posteroventral lobes of the propodeum.
 * PetW: Maximum width of the petiolar node in dorsal view.
 * PnL: Pronotal length measured from the anterior edge of the pronotal collar to the pronotal-mesonotal suture parallel to the measuring axis.
 * PpH: Maximum height of propodeum measured tangentially to the line measuring PpL.
 * PpL: Measured one of two ways:
 * Propodeal length measured from the metanotal groove to the posterior-most point of the propodeal lobes or metapleural flanges measured in lateral (side) view.
 * When viewing at an angle that maximizes length (approximately parallel to fourth abdominal tergite), perpendicular distance from line tangent to anterior inflection point (narrowest point when postpetiole is hourglass-shaped where it joins the helcium, point immediately anterior to node when helcium is sharply differentiated from node as a distinct cylindrical stem) to line tangent to posteriormost lobes if bilobed, to posteriormost point if globular.
 * PpW: Postpetiole width measured as the maximum width of the postpetiole, in same view as and perpendicular to postpetiole length.
 * PronW: Maximum width of the pronotum in dorsal view.
 * SPL: Propodeal spine length measured from the tip of propodeal spine to the closest point on outer rim of the propodeal spiracle.
 * TL: The total outstretched length of the ant from the mandibular apex to the gastral apex; when measured in profile the sum of Mandibular length + head length + mesosomal length + lengths of waist segments + length of gaster.

Specialised Indices
Note that in about 70% of cases indices are multiplied by 100 (giving a range of 0-100) rather than being expressed as simple ratios (with a range of 0-1).
 * ACI: antennal club index. This index attempts to quantify the degree of distinctness of the club. The product of segment length and width is a proxy of overall segment size, and the index measures relative change in size from segment 10 to 9 compared to relative change from 9 to 8. A sharply differentiated two-segmented club will have segment 10 much larger than 9, and segment 9 about the same size as 8, and the index will be greater than zero. A club in which segments 10 to 8 gradually decrease in size will have similar first and second terms in the formula, and the index value will be near zero. A distinctly 3-segmented club will have a value less than zero.
 * MTI (Mandibular Torular Index). In full face view the distance between points where outer margins of fully closed mandibles intersect anterior clypeal margin, divided by distance between outer-most points of lower margins of toruli.
 * OI (ocular index): EL/HL x 100.
 * PetI (petiole index): PW/PL x 100.
 * PetHI (petiole height index): PTH/PTL x 100.
 * PetWI (petiole width index): PTW/PTL x 100.
 * PpWI (postpetiole width index): PPW/PPL x 100.
 * SPI (propodeal spine index): SPI/WL X 100.

The following measurements were used by Jack Longino as part of his work on Crematogaster.