Zombies and Uninvited Guests: Who Would be a Wood Ant?

Naturalists are lucky people.  Our worlds are full of wonders and we can find magic under our noses wherever we are.

In September I paid my old friends Gus and Tess a visit.  They live in Speyside amongst the magnificence of the old Caledonian pine forests.  Gus is a zoologist by training, and Tess a botanist, but both are naturalists of wide interests and experience.  The evening I arrived Gus had just returned from an outing with an ant expert to search for a creature called the Shining Guest Ant, and as both Tess and I were keen to benefit from his new knowledge we went out to look for it the next day.

The nests of Wood Ants (Formica sp) are a conspicuous feature of the pine forests, mounds of fallen pine needles forever patrolled by their makers.  They are also an attractive source of food and security for other organisms that can cope with the massed throngs of formic-acid-squirting and pincer-jawed inhabitants, and amongst these other organisms are the Shining Guest Ants (Formicoxenus nitidulus).

It was a cool grey day, not very promising, but with Gus’s newly acquired knowledge we soon found an appropriately located nest and crouched down to scrutinise the ants moving about on its surface.  However the first ant that drew my attention was an unnaturally static one.  Courtesy of my extremely close-focussing Pentax Papilio binoculars (there is more about these in a post I will bring across from LinkedIn) I could see that it was frozen in an odd position, with its jaws clamped firmly to a dead grass stem protruding from the nest.  Gus diagnosed its problem as a fungal infection – there is a genus of parasitic fungi, Cordyceps, that specialises in feeding on the innards of ants.  In order to spread from ant to ant it has evolved the fiendish technique of infecting the ant’s brain so that is impelled to climb up a twig or grass stem, bite down hard then die, firmly fixed in place.

Zombie Wood Ant – photo by Gus Jones

Shortly thereafter the fruiting body of the fungus bursts forth from the head of the ant to scatter its spores on the ground below where its sisters are scuttling about and so get infected in their turn.  Give me athlete’s foot any day!

Further diligent searching revealed several Shining Guest Ants.  They were not easy to pick out at first, but once spotted were readily distinguished.  They are much smaller than the wood ants and quite differently proportioned – longer-bodied and shorter-legged – as well as having distinctively glossy amber-coloured bodies.  They showed up best when wandering across the golden birch leaves that had fallen on the nest.

Wood Ant and Guest – photo by Gus Jones

Unlike some other members of their genus which are duller in colour and rely on going undetected by mimicking the scent of their hosts, Shining Guest Ants have been found to secrete a substance that is sufficiently repulsive to make the wood ants drop them after grabbing them – something that happened quite frequently.  I wonder too, if the Shining Guest Ant’s extreme glossiness has a part to play in this, perhaps reflecting a cuticle strengthened to resist repeated grabbing in their hosts’ powerful jaws, or varnished to make them difficult or possibly unpleasant to grasp (think fingernails squeaking down blackboards!)

Shining Guest Ant – photo by Gus Jones

An on-line search for more information on the nature of the Shining Guest Ants’ relationship with the Wood Ants was inconclusive and left me with the impression that we do not really know if they solicit food from their hosts, raid their larders, scavenge their leftovers, eat their offspring or a combination of all of these.  About the only thing that that seemed certain was that the ones we were seeing on the surface of the wood ant nests were not foraging workers but males on the lookout for virgin queens.  Still so many mysteries under our noses that we have yet to unravel!

At least part of the attraction of these little creatures lies in their English name.  I find such triple-barreled names with unexpected descriptors very appealing, and the Shining Guest Ant now joins the pantheon along with such delights as the Trembling Sea Mat, the River Jelly Lichen and the Kinabalu Friendly Warbler.

So, we had a good day.  There is, however, a downside to being a naturalist.  As the eloquent and visionary American conservationist Aldo Leopold wrote in 1948 ‘One of the penalties of an ecological education is that one lives alone in a world of wounds’.  The loneliness is not so great these days of increased environmental awareness, but there are an awful lot of environmental issues to be aware of, and the attention spans of press and public are generally too short to achieve sustained solutions.  For many years Gus, an expert on Capercaillie (Tetrao urogallus), that rare giant woodland grouse, has been battling inappropriate developments in the mountains and forests of the Cairngorms.  As time has gone by he has cast his net wider in the quest for other organisms that will help him make the case that ancient Caledonian pine forests are not the right places to build holiday homes and retirement bungalows.  I fear he places too much faith in the power of Shining Guest Ants and other rare or little-known invertebrates, but it is good to know that he is out there, fighting the battles.  Tess’s mother is 102 and Gus’s mother was also a centenarian, so with that outstanding genetic heritage I look forward to them continuing to hold housing developers and the Cairngorms National Park Authority to account for many years to come!


Martin, S. et al (2007)  Chemical deterrence enables a socially parasitic ant to invade multiple hosts.  Proc. R. Soc. B, 274: 2717-2721.