How Do Ants Navigate?

When ants leave their nest to search for food, how do they find their way back?

The Saharan desert ant lives in colonies and makes a living by scavenging the dead carcasses of insects.

Individuals leave the burrow and search for food at midday when temperatures at the surface can reach 60°C (140°F) and predators hide from the heat.

Foraging trips can take the ants hundreds of meters an impressive distance when you consider that the ants are only about a centimetre long.

But when an ant returns, it doesn’t follow the same wandering route it took away from the nest. Instead, its return path is a straight line.

Also read: Unique behaviours among wild animals.

Once individuals are close to the nest, they engage in a characteristic set of back-and-forth U-turns until they find their nest hole.

How do they know how far they are from the nest?

Early work on navigation in desert ants showed that they use the Sun’s position as a compass meaning that they always know the approximate direction of the nest relative to the Sun.

But how do they know how far to go?

Experiments had shown that the ants do not use landmarks to navigate, so Matthias Wittlinger and co-workers set out to test a novel idea.

The biologists proposed that these ants know how far they are from the nest by using information from leg movements.

According to this pedometer hypothesis, the ants always know how far they are from the nest because they track the number of steps they have taken and their stride length.

The idea is that they can make a beeline back toward the burrow because they integrate information on the angles they have travelled and the distance they have gone based on step number and stride length.

If the pedometer hypothesis is wrong, however, stride length and step number should not affect an ant’s ability to return to its nest.

This latter possibility is called a null hypothesis.

A null hypothesis specifies what should be observed when the hypothesis being tested isn’t correct.

To test their idea, Wittlinger’s group allowed ants to walk from a nest to a feeder through a channel a distance of 10 m.

Then they caught ants at the feeder and created three test groups, each with 25 individuals.

By cutting the lower legs of some individuals off, the biologists created ants with shorter-than-normal legs.
Some individuals were left alone, meaning that they had normal leg length.
By gluing pig bristles onto each leg, the biologists created ants with longer-than-normal legs.

Next, they put the ants in a different channel and recorded how far they travelled in a direct line before starting their nest-searching behaviour.

The ants with stumps stopped short, by about 5 m, before starting to search for the nest opening
The normal ants walked the correct distance of about 10 m.
The ants with stilts walked about 5 m too far before starting to search for the nest opening.

To check the validity of this result, the researchers put the test ants back in the nest and recaptured them one to several days later, when they had walked to the feeder on their stumps, normal legs, or stilts.

When the ants were put into the other channel to “walk back,” they all travelled the correct distance of 10 m before searching for the nest.

Interpreting the Results.

The pedometer hypothesis predicts that an ant’s ability to walk home depends on the number and length of steps taken on its outbound trip.

Recall that a prediction specifies what we should observe if a hypothesis is correct.

Good scientific hypotheses make testable predictions that can be supported or rejected by collecting and analyzing data.

In this case, the researchers tested the prediction by altering stride length and recording the distance travelled on the return trip.

Under the null hypothesis in this experiment, all the ants altered and unaltered should have walked 10 m in the first test before they started looking for their nest.

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