Who sees the queen in the empire of the blind? That’s a very pertinent question for entomologists who study termites – sightless social insects that live in vast colonies united in the service of a fertile royal couple.
Non-royal termites – the overwhelming majority of any colony – behave differently towards kings and queens than to each other, but until recently the simple question of how they recognised royalty had been unanswered.
Now, researchers led by Coby Schal of North Carolina State University in the US have found the answer. Royal termites exude a wax-like hydrocarbon called heneicosane that acts as a signal, informing the blind workers when they are in the presence of the posh.
“This is the first report of a queen recognition pheromone in termites and the first report of a king recognition pheromone in insects,” says Schal.
To make their finding, the researchers used gas chromatography to identify chemicals present on the exoskeletons on royal and non-royal termites belonging to the species Reticulitermes flavipes. Heneicosane was found only on kings and queens.
When the substance was applied to termite-sized glass dummies, workers coming into contact with them started to shake – a kind of royal greeting. The shaking grew in intensity when the heneicosane was mixed with another pheromone found on the workers themselves, which thus represents the smell of the colony.
“Termites use a two-step recognition process – the colony’s odour gives workers a ‘home’ context and heneicosane within this context denotes ‘royals are in the home’,” Schal says.
Ants, bees and social wasps are also known to use hydrocarbons as identification signals for colony royalty.
The discovery of the same process in termites is significant because despite a superficial similarity in appearance and living arrangements, they are not closely related to ants.
Ants are members of an order known as Hymenoptera, while termites are classified in the order Isoptera, along with cockroaches.
Schal and his colleagues say their findings indicate that royal pheromones first evolved about 150 million years ago – around 50 million years before ants started using them. Their presence in both orders, they suggest, is an example of convergent evolution.