Red wood ants, Formica aquilonia and F. rufa (Hymenoptera:
Formicidae), are very common in forests of Sweden. In fact, species
of the genus Formica are often the dominant ants of forests
throughout the northern hemisphere. F. aquilonia is the most
prevalent species in Norway spruce forests of middle Sweden (e.g.,
Värmland) where they may build nest mounds of dried spruce needles
and twigs of a meter or more in diameter and height. The workers
vary in size from about 0.5 cm to 1 cm in length with a red thorax,
black abdomen, and red and black marked head. The ants are both
scavengers and general predators of insects, carrying many soft-
bodied caterpillars, flies, and sawflies along their several major
trails back to the nest (McNeil et al. 1978; Vielma et al. 1982;
Mabelis 1984; Ito & Higashi, 1991; Mahdi & Whitaker 1993). In
addition, a major food source is the honeydew of aphids in the
genus (Cinara) which are tended and protected by the ants
(Holopainen & Soikkeli, 1984). Red wood ants are undoubtedly
keystone species (i.e., without them the ecosystem changes
fundamentally). When red ants are removed by certain forest
practices, it has been found that many herbivorous insects become
damaging to forest trees (Skinner & Whittaker 1981; Gösswald 1984;
Whittaker & Warrington, 1985). In forests weakened by pollution and
acid rain in central Europe, red wood ant populations are often
endangered for little known reasons which in turn causes further
imbalances in predator-prey dynamics and the ecosystem (Gösswald
Gösswald, K. 1984. The relocation of Formica lugubris. Z. Angew.
Gösswald, K. 1985. Wood ants as indicators of forest diseases with
special reference to mass breeding of females. Z. Angew. Zool.
Holopainen, J.K., and Soikkeli, S. 1984. Occurrence of Cinara pini
(Homoptera: Lachnidae) in Scotch pine (Pinus sylvestris)
seedlings with disturbed growth. Ann. Entomol. Fenn.
Ito, F., & Higashi, S. 1991. An indirect mutualism between oaks and
wood ants via aphids. J. Anim. Ecol. 60:463-470.
Mabelis, A.A. 1984. Interference between wood ants and other ant
species (Hymenoptera: Formicidae). Neth. J. Zool. 34:1-20.
Mahdi, T., & Whittaker, J.B. 1993. Do birch trees Betula pendula
grow better if foraged by wood ants?. J. Anim. Ecol.
McNeil, J.N., Delisle, J., & Finnegan, R.J. 1978. Seasonal
predatory activity of the introduced red wood ant Formica
lugubris (Hymenoptera: Formicidae) at Valcartier, Quebec
Canada, in 1976. Can. Entomol. 110:85-90.
Skinner, G.J., & Whittaker, J.B. 1981. An experimental
investigation of interrelationships between the wood ant
Formica rufa and some tree canopy herbivores. J. Anim. Ecol.
Vielma, Orozco, P.E., Mackay, W.P., & Mackay, E.E. 1982. Evaluation
of Formica haemorrhoidalis as an agent of biological control.
Southwest. Entomol. 7:263-268.
Whittaker, J.B., & Warrington, S. 1985. An experimental field study
of different levels of insect herbivory induced by Formica
rufa predation on sycamore maple (Acer pseudoplatanus) III.
Effects on tree growth. J. Appl. Ecol. 22:797-812.
image (C) 1995 by John A. Byers