F. rufa is polymorphic but it is not that distinctive as Serafine said. There are a few kinds of polymorphism (I will try to translate): 1-phase allometry
-Camponotus castaneus, 2-phases allometry
-Atta texana, and three-phases allometry
- Oceophylla smaragdina, total dimorphism
- Pheidole fallax). All of that is decribed in E.O. Wilson's
"The Insect Societeis".
Polymorphism means that two body parts (for example head width and pronotum (part of thorax) width) change ratio between them depending on growth of a worker. I suppose that F. rufa belongs to 1-phase allometry kind of polymorphism.
Beside that there is also monomorphism 8i (all body parts have the same ratio even if the ant is bigger than its sister).
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The short description of behavior related to size and age of the ant is shortly and nicely described
here:
"
Context-dependent specialization in colony defence in the red wood ant Formica rufa" - T.Parmentier, W. Dekoninck, T. Wenseleers
<page 162>
"Red wood ants (F. rufa group) are moderately polymorphic, displaying
a pronounced size variation (4.5e9 mm), but lack discrete
subcastes with shape specialization (van Boven,1977). Red wood ant
workers have been reported to perform different roles according to
both age and size (Herbers, 1979; Higashi, 1974; McIver & Loomis,
1993; Parmentier, 2010; Tanner, 2008; Wright et al., 2000). Young
workers nurse the brood (mainly small, young workers) or do not
participate in tasks (mainly large, young workers). Workers of intermediate
age are engaged in intranidal building (mainly small
workers) or repairing the nest surface (mainly large workers).
Finally, the oldest workers tend to forage for food. Small, old workers
are mainly allocated to aphid tending close to the nest, whereas
large, old workers mainly hunt for prey and tend aphids at larger
distances. Large red wood ant workers are more aggressive towards
conspecific workers (Batchelor & Briffa, 2011). Ant workers can
switch task depending on the needs of the colony (Holldobler € &
Wilson, 1990). However, foragers in red wood ants, in particular,
are rather consistent in doing their task (Parmentier, Dekoninck, &
Hendrickx, 2012; Rosengren & Fortelius, 1986)."
But.. the game cannot be that em.. let's say natural, I suppose
More facts abouf F. rufa you can find in "
Ants of Poland" page 72 (version from 2002) or "
"British ants, their life-history and classification" page 241 (1915).