Small but significant – saving the narrow-headed ant

The wood ants and related species are known as ‘keystone’ species because they perform many critical roles in the forest ecosystem:

• Dispersing seeds from plants
• Boosting the growth and health of trees and shrubs by preying on herbivorous insects
• Providing habitats for many other specialist insects that live in ants’ nests
• Contribute to nutrient cycling in forests
• Providing an important food source for bird species such as green woodpecker and capercaillie
• Influencing the distribution and number of many other tree, ground and below-ground insects

Ants are tiny but they punch well above their weight in the pine forest ecosystem.

The narrow-headed ant is a very rare species in the UK, found at only six sites, four of which are in the Cairngorms. Mar Lodge Estate is the only known site on the east of the Cairngorms, with only 19 nests occurring in two distinct areas. This is an isolated, fragmented and therefore extremely rare and precarious population. Narrow-headed ants have many similarities with the true wood ants (colour, build nest mounds, insect predator, milk aphids, etc), but they also have quite distinct differences. Firstly, the narrow-headed wood ant can be identified from having a distinct indentation in its head, making it look heart-shaped, which the other ants don’t have. Secondly, the narrow-headed ant needs and loves the sun – for good reason. A certain temperature needs to be reached within their nest mound to allow successful development of their brood. True wood ants build very large nest mounds, supporting huge colonies of ants, and create enough metabolic heat amongst themselves for the nest to reach the temperature necessary for brood development. However, the less showy narrow-headed ant builds a much smaller nest mound, with fewer ants, and as a result they cannot generate enough metabolic heat. Their solution to this problem is to seek out the sun. This means that the narrow-headed ant has evolved to be more of a forest edge and glade species rather than the true wood ants, which live deep within the shady forest. At their chosen forest edge location, narrow-headed ants can both remain in the sun to ensure they receive the warmth they require, while also being near to trees for foraging.

At Mar Lodge Estate, the pinewoods have been declining over the last few centuries due to exploitation for timber, clearance to create grazing land and high deer densities that prevent regeneration. This has resulted in a very open forest in places, with only scattered trees, and a low canopy cover. The narrow-headed ants that remain occur well within this scattered forest and far from the forest edge. They have survived here as it’s open to the sun and trees provide a habitat for foraging. However, in recent years we have been encouraging regeneration of the forest at Mar Lodge through reducing deer numbers. The great success of this has meant that young pine and birch trees are now growing thick and fast around the ants’ nests, creating significant shade. Our monitoring has indicated that some of the nests are reducing in size and activity, and a few nests have already been abandoned. Unfortunately, narrow-headed ants have limited dispersal capabilities. They can perform colony-budding (moving a short distance from their current nest) and they do undertake mating dispersal flights, but only over short distances and not at the pace our forest has surrounded them. After much consideration and discussions with relevant ant experts, we decided that to ensure their long-term future success without the need for regular active intervention (such as continually clearing the tree regeneration around their nests) we had to try and move the ants to the forest edge. Once at the outside edge of the forest and in a suitable habitat, the ants will have far more opportunities to move with the forest as it slowly expands.

So, how do you go about moving ants? Working in partnership with the Cairngorms National Park and the James Hutton Institute, we were lucky enough to secure funding from CLIF for our exciting translocation project of narrow-headed ants at Mar Lodge Estate. The project involves attempting two translocation methods:

1. Catching winged sexual males and queens from the nest when they emerge in July, bringing them into captivity to mate and then putting mated queens out into suitable sites in the hope they’ll establish new nests.

2. Translocating whole nests to new suitable locations.

The first method is obviously less invasive and risky, and we tried this in 2020. To be honest, at first we wondered how on earth we would ever manage it! However, amazingly we did – with the help of some family members and local volunteers. In July, when the sun comes up in the early morning (7am onwards and the midgies are hell!), the winged sexual males and new queens appear on the surface of the nest before they take off on mating flights seeking other males and queens. These ants are easy to spot as they are the only ones with wings. The tricky bit is scooping them up when they suddenly appear on the nest – a winged grain of rice-sized insect moving at lightning speed among hundreds of wingless worker ants darting around the nest and diving for cover back into the nest as soon as they sense movement. Even harder is trying to do this when wearing a midge head net and visibility is obscured by a thick cloud of midgies around your head. Many hours were spent staring at nests at sunrise, but miraculously over a few weeks we successfully caught a good number of winged males and queens from a few of the nests that were healthy and producing them.

Back in our invertebrate lab (converted office!) we looked after the ants, keeping them fed with sugar solution and apple, and when we had appropriate males and queens we carried out mating trials in a tank. We always mated males and queens from different nests, to ensure mixing up the genetics as would happen in nature. For the trials we would simulate the early morning by keeping the ants in the dark and then we’d switch on a directional lamp to simulate the sun coming up. This worked well and we observed the males getting excited and successfully mating with the queens. Sadly, the males naturally die after mating. However, we would catch the females and release them into the new suitable area at the edge of the forest where we’re hoping to establish new nests.

Hopefully I have already convinced you that ants are fascinating. Well, wait till you hear this – more stuff for the filmmakers! Narrow-headed ant queens often establish new nests through a behaviour called ‘temporary social parasitism’. Basically they seek out another species of ants’ nests (in our case usually a tiny species called Formica lemani), go into the nest and lay their eggs. The Formica lemani ants look after the eggs and feed the larvae as their own until the ants develop. Once the narrow-headed ant eggs have hatched and developed they stage a coup, taking over the Formica lemani nest and making it a new narrow-headed ant nest.

In 2020 we managed to release 20 mated narrow-headed ant queens into a new area which we know supports Formica lemani and we will repeat this work in 2021. It’ll be exciting to revisit the area where we released the queens and see whether we can find any new nests. If it has worked and we have successfully established narrow-headed ants in a new suitable area of Mar Lodge Estate, we’ll have helped secure the future for this amazing species.

In autumn 2021 we’ll also try whole nest translocation. Due to the risky nature of this, we’ll attempt to move just two nests – those most at risk from shading from current vigorous tree regeneration. The method is quite simple in theory – we’ll carefully dig up the narrow-headed ant nest, ensuring we dig down far enough to get all the nest material while trying to minimise disturbance to the nest structure. The nest, complete with ants, will then be placed in a hessian sack and carried to its carefully selected new site at the forest edge. The nest will be gently placed down here, along with any loose thatch material. For a few weeks after translocation we’ll provide supplementary feed to the ant nests to ensure they have a good food supply and plenty of energy to repair the nest structure as required. This will be the first time narrow-headed ants have been translocated in Scotland, although other wood ant species have been successfully ‘rehoused’ as part of the dualling of the A9 trunk road. These translocations have shown that the ants sometimes rebuild the translocated nest, but often they build a new nest close to the translocated nest and abandon this one. After moving the nests we’ll monitor them regularly to determine whether the translocations have been successful.

Clearly, the results of our work are still to be seen. We sincerely hope we’ll be successful in moving the ants to a location where they can survive and flourish without the need for further intervention in the long term. Hopefully this will mean a rosy future for this small but mightily important pinewood species at Mar Lodge Estate.