Discovering Species – Wood Ant

I could get lost in watching a wood ant nest for hours… if standing next to one didn’t make me an immediate target for the little guys to start nipping to warn me off. Their enormous nests may be made from dead vegetation, but seem almost alive in themselves. I find it mesmerising to see the surface teeming with busy ants. I’m quite happy to be entertained by watching wood ants any time, but saw a behaviour I’d not seen before on my most recent visit to the woods. It made me even more aware of how sophisticated they are and spurred me on to find out more about them.

Basics
Common name
Wood Ant, Red Wood Ant

Scientific name
Formica rufa (also known as the Southern Wood Ant, this is the species of Wood Ant that I have encountered and pictured in this post.)
Other species of Wood Ant in the UK include:
• Formica lugubris (Hairy Wood Ant/Northern Wood Ant)
• Formica aquilonia (Scottish wood ant)
• Formica pratensis (European wood ant) – Presumed extinct on mainland Britain in 2005

Order
Hymenoptera – includes sawflies, wasps and bees, as well as ants.

Habitat
Wood Ants are reportedly most frequently (and unsurprisingly) found in forest habitats and woodland edges, as well as heathland and dry grassland. They are said to require some gaps in the woodland to allow sunlight through to warm their nests. For this reason, as explained by woodants.org.uk, ride widening and maintenance of glades on woodland sites to provide sunny areas is important to ensure the ants have the habitat they need. I have seen myself that they take advantage of the material and available light in coppiced areas. However, they are also said to be adaptable enough to build nests in adjacent heath and scrub when the food availability is sufficient. Activities which threaten their habitat include deforestation, human disturbance, inappropriate planting of trees in areas where there was previously no tree cover, and agriculture, and the range of some species of wood ant is getting smaller.

Distribution
I wasn’t really aware of Wood Ants before I started working on an ancient woodland site. I was in awe of the size (some almost as tall as me!) and level of activity of their nests, and quickly found out that you have to take care not to accidentally stand in an “ant highway”! After “discovering” them, I wanted to know where else they are found. According to AntWeb the Southern Wood Ant has been recorded in Canada, the United States, Austria, Belgium, Bulgaria, Czech Republic, Denmark, Finland, France, Germany, Italy, Latvia, Netherlands, Norway, Poland, Russia, Spain, Sweden, Switzerland and the United Kingdom. It is considered one of the wood ant species which is locally common and widespread, but because of lack of recording in national datasets, their distribution is not well understood.

IUCN Status
The Southern Wood Ant is classified as Near Threatened on the IUCN Red List. In this listing, population trends are unknown, as is the ability of populations to disperse and cope with fragmentation of forest habitat.

Inside the Nest
Structure
In awe as I am of wood ant nests, I wouldn’t dream of destroying one for my own interest, but I’d love to be able to somehow slice into one to see a cross section. There’s a brilliant diagram on woodants.org.uk which satisfies my curiosity. It shows that the nest is full of interconnected chambers for different purposes, including the egg-laying queen, brood development, food storage, disposal of deceased ants and a waste compartment. The recognisable thatch on the top of the nest also provides a roof for rainwater to run off and keep the inside of the nest dry. Incredibly, the enormous height of these nests can continue well underground, making them potentially double (or more) the size that can be seen above ground!

Life Cycle
I’ve been fascinated to learn a bit more about the wood ant life cycle. Who knew that they develop in cocoons?! (Maybe everyone except me, but I was amazed to read it). Other interesting details include that the developing grubs which will eventually become queens are fed more to make them bigger, and the fertilised eggs hatch into females, and the unfertilised eggs become males. The queens can live for 15-20 years, males survive for a few weeks, and workers (except for those which overwinter with the queen) live for about two months. I made a little cycle diagram to illustrate the main stages of their life cycle.

Interesting Behaviour – Aphid “Farming”
I think I had heard of ants farming aphids some time ago on a nature programme and allowed it to drift to the back of my mind, probably thinking it was something I’d never actually see in real life. When I was looking at saplings recently, searching for individuals to put tree guards on, someone pointed out that the ants were busy interacting with the aphids on the young plants. I was so pleased that this was something I could see up close. I read a bit more about this interesting relationship to find the information below.

Why they do it
Wood ants have a varied diet which includes other insects, other ant species and honeydew (the excess sugars excreted by aphids, which eat tree sap). Workers fill their abdomens with honeydew and regurgitate it for other workers and the queen when they return to the nest. The developing grubs which the workers feed require insect prey for protein rather than the honeydew.

How they do it
Wood ants “milk” the aphids of honeydew by massaging their abdomen. They also help to protect the aphids, by defending them against predators and moving them to places which are better for them to feed. The relationship is therefore mutualistic (benefits both species). I hadn’t made the link that this is why you see ants climbing up and down tree trunks – they will make their way up to the canopy to reach aphids which live up there.

I couldn’t be more enthusiastic about this species. As well as being fascinating in their own right, with their sophisticated behaviours and almost constant activity, they give me a sense that the woodland is theirs. I very much feel like a visitor and that the wood belongs to them – that it has done since long before my time, and will continue to do so beyond my years. It’s humbling to be surrounded by their massive nests and aware of their presence all around, and I highly recommend visiting a site where you can experience them first-hand if you’ve not already done so!