Ants can be spongers too! ‘Lazy’ insects found in colonies that spend half their time inactive while others work around them

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They are known for being some of the most industrious creatures on the planet with each ant spending their lives working for the benefit of their colony.


But it seems that, much like in human society, there are some ants that just do not pull their weight.

Researchers have discovered there are some worker ants that appear to be just lazy – and they make a living out of it.

The findings suggest these ants may be part of a previously unrecognised caste of workers in the colonies of these social insects, or could just be selfish individuals.

Scientists in the past had assumed the ants they found in nests apparently being idle were merely taking a rest from their normally busy days.

However, biologists at the University of Arizona recorded the behaviour of these ants over a three day period to find out.
They discovered that these idle ants actually spent half their time immobile doing no jobs at all.

Daniel Charbonneau, who led the work, said it was still unclear whether these ants were performing some other task within the colony that required them to be inactive.

But he said it was possible the ants were merely just more selfish and so attempting to conserve their energy at the expense of others.

He said: ‘We show that the level of inactivity is consistent for individual workers, but differs significantly among workers, that is, some workers effectively specialize on ‘inactivity’.

‘We show that ‘inactive workers’ form a group distinct from other task groups. Hierarchical clustering suggests that inactivity is the primary variable in differentiating both workers and tasks.’

Mr Charbonneau and his colleague Dr Anna Dornhaus, whose work is published in the journal Behavioral Ecology and Sociobiology, marked 250 worker ants from five different colonies.

image of the lazy ant guy

Using cameras they recorded their behaviour over three days and built up a database of activity for the individual ants.

They also studied the circadian rhythms of the insects and found while worker ants do work in shifts, it does not explain why some of the ants were consistently less active.

Mr Charbonneau said, however, it was possible the inactive ants may play an important role within the colony.

In further experiments he is removing the laziest ants from colonies and studying what impact this may have.

Worker ants often have highly specific roles within a nest with some responsible for building the nest, others for cleaning, some gathering food and others feeding larvae.

In some species of ant, specialised workers produce a sugary liquid to feed others around them, like in honey pot ants.

These feeder ants hand from the roof of their nest and their abdomens swell with the ‘honey’ they produce.

However, no such obvious behaviour is evident in other species like Temnothora rugatulus studied by Mr Charbonneau and his team.

It is possible these ants are secreting food at a lower level or may even be producing antibiotic material to help keep the nest free from infection.

However, the ants could also merely be a reserve workforce, resting until such a time as they are needed.

Previous work by Mr Charbonneau and his colleagues has shown the inactivity levels in the next go down when there is more work to do.

They also found activity tends to be seasonal, with more idle ants in the autumn than in the mid-summer.

He said: ‘As much as 60 per cent of an ant colony is inactive at any one time.

‘There are individual differences in inactivity levels as there are some workers who are always more inactive than others.’

Speaking to New Scientist, he added that it was possible the lazy ants were merely older individuals who had slowed down.

Tomer Czaczkes, who studies ants at the University of Regensburg in Germany but was not involved in the research, said: ‘The apparently “lazy” ants could also be acting as a reserve fighting force, since raiding, including raiding for slaves, is quite common amongst such ants.’