The seed-harvesting ant Vermomessor pergandei (now Messor pergandei) is a harvesting ant common in the deserts of southern California, Arizona, Baja California, and Sonoran Mexico (Creighton 1953). It displays a high degree of worker size variation, having a body length size range from 3.5mm to 8.4mm. The variation in size is described as monophasic allometry (allometric relationships with single slope, Rissing 1987).

Published morphological data on this species has used head width (Rissing and Pollock 1984, Waser 1998), mandible length (Davidson 1978) and body mass (Feener and Lighton 1991, Lighton et al. 1994). The motivation for using these measures stems from their ecology as seed-harvesting ants, inferring head width and mandible length play an important role in determining seed size harvested. 

Evidence suggests variability of mandible size (correlated to body size) decreases as competition increases (Davdison 1978). However in this species seed size and worker body size is not 'size-matched', in that larger workers do not necessarily carry the largest seeds as foraging theory predicts (Rissing and Pollock 1984, Waser 1998). Although there is some evidence there is task-matching of seed size and worker size over short term periods (hours or days, Waser 1998). 

Published Body Size Measurements:

Body length 3.5-8.4mm (Davidson 1978)

Head width 0.8-1.88mm (Rissing and Pollock 1984, Rissing 1987)

Mandible length 0.5-1.05mm (Davidson 1978). 

Dry body mass of 0.12-3.25mg (Feener and Lighton 1991)

Live body mass ranging from 1.33-11.03mg (Lighton et al. 1994)