Sunday, October 10, 2010
Aculeata Agonistes: Ants, Aphids & Aspen
Aspen Parkland biome, named for its dominant tree, Quaking Aspen (aka White Poplar) Populus tremuloides, and its park-like mixture of open grasslands and patches of trees. In the Prairie Provinces of Canada, Aspen Parkland is rich in postglacial water bodies. And, as my late father-in-law pointed out repeatedly, he used to going boating in what is now our neighbourhood when he was a boy.
Formica podzolica Francoeur, 1973.
In zoological nomenclature, the year that comes after the author of a species name refers to when the diagnosis of a new species was first published. In this case, I haven’t inverted the 9 and 7 – this species name wasn’t properly sorted out until 1973. Before that it travelled under several names including the widely distributed Formica fusca. Insects tend to be interesting in direct proportion to how much one can learn about them and unless one can first learn their real name, such information as to make them interesting neighbours remains elusive. Ant species are particularly difficult to identify – species level keys are technical, and, well, many ant species tend to look alike. This seems to be especially true of Formica species. In this case, we are indebted to James Glasier for identifying the black ants that caught our attention with their herds of speckled aphids on young aspen as Formica podzolica (misattributions in any other images are mine).
sap-sucking homopterons (aphids, hoppers, and the like). They protect these annoying insects from ‘natural enemies’ such as ladybird beetles, lacewings, and small parasitic wasps. ‘Natural enemy’ is another of those bizarre concepts that has somehow become commonplace. Are there unnatural enemies? Well, I suppose Count Dracula’s cockroach-munching Igor would do. In any case, usually ‘natural enemy’ refers to an arthropod that eats or parasitizes an arthropod that eats something we value. Ants can be natural enemies, but not when they are guarding aphids. By chasing off or killing things that want to eat aphids, ants allow plant lice (= aphids) numbers to rise, the amount of sap they drink to increase, more honeydew to spatter, and sooty molds to cover leaf surfaces. None of this would seem to be good for the plant, but the ants benefit by ‘milking’ the aphids for their honeydew and the aphids are assumed to do better with the guards.