Wood Ants
There are a number of different species of wood ant.
The one that is common in England is Formica rufa. The one that is commonest in the remnants of the Scottish Caledonian pine forest is Formica aquilonia. When you come across the conical nests of wood Ants in the Black Wood of Rannoch it will most likely be nests of Formica aquilonia that you are seeing.
Creative Commons - credit VillaK
The nests may be up to a metre high and are largely constructed of pine needles. The main nest may be surrounded by satellite nests which are smaller. The ants lay down pheromones between the nests and also up trees to guide their fellow workers to sources of food such as aphids. Wood ants (and many other ants) have a symbiotic relationship with aphids. The aphids suck the sap of plants, including trees and the sap has more sugar than the aphids need so they excrete it in the form of honeydew. The sweet honeydew is very attractive to ants because they get plenty of protein from their invertebrate prey but not much carbohydrate. The ants tend the feeding aphids and drink the honeydew from time to time as it is produced. In return the ants protect the aphids from predators and parasites such as ladybirds or Brachonid wasps. This kind o relationship where both species benefit is allied symbiosis.
In the Black Wood of Rannoch the aphids are often those that feed on the Scots pine (Cinara pini). This is a large grey aphid with formidable mouthparts allowing it to penetrate the phloem vessels of the pine twigs.
When the BBC were making the David Attenborough programme ‘Life in the Undergrowth’ I showed a representative the largest nests in the Black Wood with a view to them being filmed for the programme. In the event they found bigger ones in Poland and used them instead.
If you look carefully at the trunks of trees in the summer you may well see ants streaming up and down the bark as they journey to and from the nest to the aphids. The ants will also catch and kill any invertebrates that they can overpower in the tree. The prey is dismembered and then carried back to the nest to feed the larvae.
Ants are social insects and in common with other social members of the insect order Hymenoptera they have an unusual genetic makeup and have different castes. The casts are - Queens, Workers and males. Some other social insects also have soldiers. The queens and workers are all female and have a double set of chromosomes - this is called being diploid. The males have only one set of chromosomes and are termed haploid.
Round about July on sultry humid days there will be a marriage flight. The new queens and males emerge from the nest in large numbers and take to the air. All the nests in the Black Wood of Rannoch synchronise this so that there can be cross fertilisation. The males try to find a queen and mate with her. Soon after mating the males die as they no longer have a function. The mated queens drop to earth and shed their wings. They may either seek out an existing nest and hope to join it or found a new nest themselves. Unusually a wood ant nest can have quite a few queens.
You will perhaps notice that nests tend to be in sunny spots. This is because the ants need warmth to make them active. In spring groups can be seen on the top of the nest basking in the sunshine. Some species of wood ant need more sunshine than others. For example Formica exsecta and Formica rufibarbis need more sunshine (warmer temperatures) than Formica aquilonia. As climate change progresses there may be a consequence for wood ants.
When the BBC was making George McGavin’s programme ‘Miniature Britain’ I was asked to show them places where ants were tending aphids for them to film. We found a good spot next to the ‘saw dust pits’ at Dall and this was used in the film. The programme also detailed the mycorrhizae which are fungi that have an intimate relationship with tree roots.
I took Ryad Black from Kinloch Rannoch, my then pupil in a biology class at Pitlochry High School, along to watch the filming. We both had an interesting day.
There are over 100 species of invertebrate including beetles, spiders mimicking ants and a wood louse that like to live inside the wood ants’ nests. They run the risk of being eaten but usually produce chemicals that cause the ants to leave them alone.
The inquilines (as they are known) benefit from the high temperature of the nest (25-30 degrees C) which is maintained by the ants, abundant food like honeydew and protection from predators.
I found this cockchafer beetle on an ants nest in the Black Wood of Rannoch - it disappeared into the nest - it is a known inquiline.
Creative Commons - credit gbohne
Wood ants don’t sting but they do squirt Formica acid. When the ant is threatened it curls its abdomen between its legs and squirts a jet of acid at the threat. If you stand near a wood ants nest the ants will see you and send little jets of Formica acid towards you. This won’t harm you but you can smell it. It is important not to disturb the nest in anyway. The ants are rare, vital to the ecology of our precious remnants of the Caledonian pine forest and are protected under law. Any damage to the surface of the conical nest can let rain in and can kill the inhabitants.
There is one remaining wood ants nest at Dùn Coillich and this is an indicator that once there was an ancient wood there. We are now replanting native trees. The ants at this nest have a Rowan tree nearby and I have watched them stream up this tree to find their aphids. The aphids are probably Dysaphis sorbi.
Wood ant species
True Wood Ants
Formica rufa - The English Wood Ant
Formica aquilonia - The Scottish Wood Ant
Formica lugubris - The Hairy Wood Ant
Formica pratensis - The European Wood Ant - went extinct in mainland Britain in 2005
Ants closely related to true wood ants.
Formica exsecta - The Narrow-headed Wood Ant - found in the Black Wood of Rannoch, Rothiemurchus, Abernethy, Braemar and Carrbridge. Formica exsecta likes open woodland or wood land edges. It is one of the ant species that helps to disperse the seeds of plants such as small cow wheat (Melampyrum sylvaticum). Plants that are dispersed this way are called myrmecochorous plants). In the Cairngorms Formica exsecta helps to maintain he right habitat for Capercaillie lekking areas.
Formica rufibarbis - The Red-barbed Ant - an ant of southern heathlands.
Formica sanguinea - The Slave-making ant.
This ant looks much like a wood ant but is slightly larger. It habitually raids the nest of other ants and steals the pupae which are taken back to its own nest to act as slaves.
A single worker will scout out the availability of a target nest for a raid. The scout returns to the main nest and summons an army of raiders who march in a column to attack the target nest. A battle will ensue in which many ants on both sides are killed or injured before the Slave-maker ant emerges victorious with its enslaved captives.
Shining guest ant (Formicoxenus nitidulus)
An ant found only in the nests of wood ants and does not make its own nests.
RSPB Scotland, the Cairngorms National Park Authority (CNPA), Buglife, Butterfly Conservation and Scottish Natural Heritage (SNH) are working together to try to protect the Shining Guest Ant which is very rare.
The large ant on the left is a wood ant and the small ant on the right is a shining guest ant.
Photo credit Stewart Taylor - displayed by linkage to the RSPB website.
