No rush hour on ant highways

The traffic congestion of Celtic Tiger days is back. During that misguided era, we commandeered huge swathes of countryside and obliterated ancient sites to make way for cars.

But the motoring monster still wants more. To paraphrase Cyril Northcote Parkinson; the number of vehicles expands to fill the space made available for them. Why can’t we utilise our existing roads more efficiently?

Cars, we are told, will soon be ‘talking’ to each other using GPS and Bluetooth technologies. Drivers will be alerted automatically when vehicles misbehave, come too close to each other, or travel too fast. Such developments may seem novel, but they’re not. The humble ants, facing similar traffic challenges, have done it all before. According to German research just published, these inventors of insect motorways are experts at highway control. Individuals on the move seem to exchange traffic-calming information routinely.

An ant nest has one or more queens whose sole task is to lay eggs. A few lazy males are tolerated in the colony; at swarming time, they will venture out to mate with flying queens. All the other residents are infertile females who perform the housekeeping tasks and take care of the young. In suitable weather, hordes of these workers exit the nest to find, and bring back, food. Among army and leaf-cutter species, there can be hundreds of thousands of foragers. Organised like a super-efficient military machine, the commuters establish routes to and from the main food locations. Their well-trodden paths, known to entomologists as ‘trunk trails’, are virtual ant-roads along which the marchers proceed in a disciplined fashion.

The black-backed meadow ant lives in the dry grass-lands heaths and roadside fringes of mainland Europe. It became extinct in Britain in 1988 and is not among Ireland’s 26 ant species. Meadow-ant workers, up to 10mm long, forage for food, especially the aphid excretion known as honeydew, which they transport along trunk trails to the nest, a large mound up to a metre in diameter. Vegetation, small stones and twigs are removed from these paths, the constant traffic flow keeping the routes maintained from year to year.

Scientists at the University of Halle-Wittenberg filmed 1,865 meadow ants moving along a 15cm section of trail. By controlling the amounts of food available to the ants, they were able to stimulate, or reduce, traffic levels. The speeds attained by 500 individuals were measured, in an attempt to discover the ant ‘rules of the road’.

If more food was offered, the colony immediately dispatched extra foragers. When traffic levels were low, the ants moved along the centre of the trunk lane but, as the number of foragers increased, they began using the full width of the trail. The travellers showed ‘some degree of lane segregation, which contributes to traffic organisation’. Workers returning to the colony moved faster than those going out. Most significantly, no matter how much the number of road-users increased, traffic-jams didn’t occur; rush hour isn’t a problem in ant society. There were collisions but they didn’t lead to pile-ups; ant ‘drivers’ don’t stop when they come upon an accident. Needless to say, ‘road rage’ is unknown in their world.

When our motorways become congested, drivers are forced to slow down. Paradoxically, ant drivers do the opposite; they move faster, the increased rate of flow prevents bottle-necks building up. The speeds of some individuals rose by up to 25%. Oddly, collisions were no more numerous when the traffic was moving fast than at ‘normal’ speeds. The mishaps, the scientists speculate, may serve a useful purpose; helping to disseminate vital between the moving columns. Physical contact might facilitate exchanges of data about conditions ahead. Could studying ants enable planners to deal more efficiently with our increasingly choked-up road networks?

Honicke, C, et al. Effect of density on traffic and velocity on trunk trails of Formica pratensis. The Science of Nature – Naturwissenschaften. 2015

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