New Scientist - USA (2020-03-07)

30 | New Scientist | 7 March 2020

Book

Desert Navigator:

The journey of an ant

Rüdiger Wehner

Harvard University Press

“CATAGLYPHIS is only an ant, but

truly what an ant,” writes Rüdiger

Wehner in the prologue to Desert

Navigator. A chapter into his new

book, I also came under the spell

of this long-legged “racehorse

of the insect world” and the

staggering navigational skills

that emerge from the 500,000

neurons in its brain, which weighs

less than a tenth of a milligram.

As a young biologist, Wehner

fell for them when he visited a

Tunisian salt pan and saw one

pick up a dead insect and sprint

100 metres across the featureless

desert to its inconspicuous nest

hole. How did the ant know where

to go? Fifty years later, thanks to

Wehner, now director emeritus

of the Institute of Zoology at the

University of Zurich, Switzerland,

and the researchers he inspired,

we have many of the answers, laid

out in this grand book.

As Wehner realised early on ,

Cataglyphis is a “model organism”

for studying animal navigation.

The ants run about on flat, open

surfaces, so it is easy to track them

and explore their talents. The

secrets revealed in five decades

of research are extraordinary.

One of the first surprises is that

these ants can do what human

navigators call “dead reckoning”:

keeping a continuous tally of both

direction and distance covered

so that they can always compute

the direction of home.

As their compass, the ants use

This ant has superpowers

The amazing desert ant runs at breakneck speeds and uses the sun, wind and

magnetic fields to navigate featureless deserts, discovers Alun Anderson

the polarisation pattern of the

sky, as well as Earth’s magnetic

field and the desert wind.

Gauging distance is done with a

“pedometer” – the ant counts its

steps – and by sensing the “optic

flow”, or relative motion, of the

ground beneath it as it runs.

If the desert contains landmarks,

such as rocks, the ants are superb

at using them for navigation too.

When an ant leaves the nest,

Wehner describes how it faces

back towards the entrance and

pauses to take “snapshots” of its

surroundings. Later, it compares

those snapshots with the current

view to spot the way home.

Wehner explains many more

fascinating ant skills before he

moves on to his pioneering

studies on the harder question

of how the ant integrates all that

Views Culture

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you might do on a stroll from a

hotel in an unfamiliar city. You

may not know where you are, but

you can find your way home by

remembering things like: “I

turned left at a big supermarket.”

Desert Navigator is written in

a concise and serious style. You

will need to give time to its many

explanatory diagrams, but the

rewards are insights into “the

process of thought that leads to

the solution”, and the ingenuity

of the experiments that Wehner

and others have devised to work

out how the ants do their thing.

For example, to show that the

insects were counting steps to

estimate distance, tiny stilts were

glued to their legs to lengthen

their stride. Sure enough, they

changed their distance estimates.

And to show that the ants really

sense optic flow, a runway was

built in the desert with a moving

pattern of stripes beneath it.

That, too, altered their perception

of how far they had run.

You will end the book as a fan

of Cataglyphis, for the creature is

more than just a navigator. Early in

life, the ants nurse the brood, then

become “excavators”, and finally,

after initial timid trips, they sprint

off from the cool of the nest into

the ferocious desert heat to forage.

Outside, their achievements

are amazing. They can move fast,

covering up to 110 body lengths

a second; in human terms, about

600 kilometres per hour. They

must dodge danger everywhere.

Robber flies attack from the air,

jumping spiders from the surface

and tiger beetles from below

ground. A forager is usually dead

within five to seven days, even

though the ants live for months

in a lab. But food must be found.

What a life and, yes, what an ant. ❚

Alun Anderson is an editor emeritus

of New Scientist

information with its memory

to decide where to go. This is

the frontier where field studies

meet computational modelling,

robotics and neuroscience.

So far, research seems to settle

one long-running debate: the ants

don’t form a mental “map” of their

surroundings as many researchers

have argued. Although they are

superb navigators, they keep

things simple. They never actually

know where they are but only

where to go. If that sounds

confusing, it is a little like what

Cataglyphis takes

“snapshots” of landmarks

to help it locate its nest

“ These insects do what

we call dead reckoning,

tallying direction and

distance so they always

know the way home”