You’re sitting in a cave. How big is the mountain above you?
A termite would be able to tell you, simply by chewing the wall.
Drywood termites live quite bizarre lives when you think about it. Next time you hear the loud noises of termites chewing inside a wood block, take a moment to think about how odd their existence must be.
Imagine being completely entombed in a cave made of delicious ham. You live in it, tunnel through it, raise your kids in it, excrete in it.
Wings and eyes are both useless, so you have dispensed with them.
At some point down the line, one generation of your unborn great-grandkids is going to find the ham runs out. And that’s a problem. They are going to have to fly off and find another mountain of ham that can sustain them and their offspring.
But – and here’s the spicy port-and-molasses rub – you have to know how much ham is left in order to know when to develop wings and fly away rather than stay and have babies. And when you find a new mountain of ham, in order to know whether it is a suitable resource for you and your future kids, you have to be able to assess how big it is.
From the inside.
How do termites know how big the wood block is without measuring it?
Some insects walk up and down a resource to measure it, like burying beetles, which walk round a dead mouse several times before deciding whether to breed on it. That doesn’t work for termites, because predators would quickly snap them up.
An experiment a few years back discovered that Cryptotermes termites actually use a form of echolocation to size up the piece of wood they’re in – and to choose between alternative blocks of wood.
Staggeringly, the termites can sense the vibrations that are caused when they make their loud chewing sounds, and the resonant frequency tells them how big the wood is.
Faced with a choice of 20mm and 160mm blocks of pine, Cryptotermes invariably chose the smaller block (probably because they are small-bodied termites and don’t want to bump into any larger ones).
But when chewing vibrations from the 160mm block were recorded and then played back through the 20mm block, the preference was destroyed. When control vibrations consisting of random noise were played through the 20mm block, there was no effect on preference.
Other insects communicate using vibrations through wood or other material – for example, treehopper babies “buzz” against their branch in structured collective patterns, using a “cooler! warmer!” method to direct their mother to the source of a predator attack. Passalid beetle larvae communicate with parents via cicada-style stridulations, while some male dung beetles produce a courtship song that is transmitted by vibrating the poo in which the female is buried. They say romance is dead…