Why cockroaches need their friends
In need of company
The much maligned cockroach is more sophisticated, and social, than we thought, according to new research.
They hide away, unseen, lurking in dark corners and crevices.
When they emerge, they aimlessly scurry and swarm, often around our houses, kitchens and supposedly dirty hotels and restaurants.
We end up despising them for their natural behaviour, seeing them as nothing more than pests to be avoided, exterminated even.
But cockroaches have in many ways been given a raw deal.
Scientists are discovering that these supposedly crude, and creepy automatons are much more sophisticated than we thought.
By unveiling the secret lives of these insects, they are finding out that cockroaches are actually highly social creatures; they recognise members of their own families, with different generations of the same families living together.
Cockroaches do not like to be left alone, and suffer ill health when they are.
And they form closely bonded, egalitarian societies, based on social structures and rules. Communities of cockroaches are even capable of making collective decisions for the greater good.
By studying certain species of cockroach, we may even be able to learn some insights into how more advanced animal societies evolved, including our own.
Living among us
A small proportion of insect species are renowned for their social skills.
Ants, termites and some bees and wasps, for example, are "eusocial insects", which have highly developed social structures and behaviours.
But while cockroaches were known to be gregarious, based on their tendency to live in groups at various stages in their lives, we understood little about how they actually behave around each other.
Hardy critter
A scientific review published in the journal Insectes Sociaux explains what we now know.
There are around 4000 cockroach species so far described by science. Of these, about 25 have adapted to live among people.Two species, the German cockroach (Blattella germanica) and the American cockroach (Periplaneta americana), have been studied in particular detail.
During the day, both rest in groups within dark cracks, crevices or pipes. At night, these groups, or herds as scientists sometimes call them, split up, with individual cockroaches roaming in search of food and water.
Research described by the review, conducted by Dr Mathieu Lihoreau of the National Centre of Scientific Research in Rennes, France and colleagues, reveals the importance of group living to cockroaches.
Home alone
Cockroaches that do not hang out with one another suffer "isolation syndromes". For example,
young German and American cockroaches left alone take longer to moult into new larger forms and eventually become adults.
Their later behaviour is also severely affected; young isolated cockroaches find it harder to join a community and mate later in life.
Young cockroaches, it seems, need to be around and in constant physical contact with one another to properly develop.
In 2010, researchers announced they had found that cockroaches "talk to each other" about food.
Dr Lihoreau's review lays out the extent to which cockroaches rely on chemical cues to pass on information about the location and type of food.
Using chemicals called cuticular hydrocarbons expressed on their bodies, the insects even communicate about which crack or shelter might make a good home for the day.
Sometimes the cockroaches lay scent trails by depositing faeces rich in these chemicals, which other cockroaches can follow.
These chemicals also allow cockroaches to identify each other - in particular recognising which other cockroaches they are related to, and how closely.
So called kin recognition "plays an important part of the [cockroaches'] social life," the researchers write.
Among other things, it "allows individuals to avoid mating with their siblings," they say.
Perhaps the most striking revelation about the secret lives of cockroaches though, is the extent to which they form "social herds" and can make collective decisions.
When seeking a shelter, for example, all cockroaches in a group will make the same choice, selecting the same, best location.
Groups also seek out the same sources of food.
Termites are a type of cockroach
Indeed, they "can be seen as emergent forms of cooperation," say the scientists, or "an emerging property of swarm intelligence".
Studies on American and German cockroaches show just how social these insects are.
They live in common shelters, different generations of related cockroaches live together, and these animals become socially dependent on one another.
And though cockroaches are less socially advanced than eusocial insects, which have highly evolved communities, they are more egalitarian.
In eusocial insects, a queen will dominate, reserving breeding privileges for herself, supported by thousands of workers.
However, any cockroach is able and allowed to mate and breed.
Dr Lihoreau and his colleagues call for more investigation into cockroach social behaviour, as it may unveil more about how single animals, scurrying around to their own ends, somehow come together to form collective groups.
Even cockroaches, it seems, are a friendly bunch, and from an evolutionary perspective are benefiting from their previously unheralded social skills.
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