Cicadas call stumps on summer song

LOUDMOUTH: The night-time noisemaker, Amphipsalta zelandica, or the chorus cicada. Scientists — and no doubt nearby residents — attest that cicadas make the loudest calls in the insect world. Picture by Roger Handford

The nightly noise of cicadas made its appearance with last week's run of hot weather, raising the question of what it means for the length of summer.

Before the rain arrived over the weekend, there was a run of hot days which raised ground temperature to trigger the cacophonous chorus.

From February 1 to 5, the daytime highs were in the mid- to high-20s, with the warmest day at 29.4.

Combined with warm moist air from the sub-tropics, this brought night temperatures up too, with “lows” such as the 19 degrees overnight Monday to Tuesday, making sleep elusive. It was much the same the past two nights.

Science, including studies in New Zealand, has now shown the cicada chorus signals that conditions are right for the insects' larvae to emerge from the ground and transform into the adult noisy form in nearby trees.

With rain temporarily damping the insects, their overnight clattering has resumed.

New Zealand has 40-plus species of cicada — but the one that annoys people the most is the annual or chorus cicada — Amphipsalta zelandica.

The adults lay their eggs in splits and crevices in the bark of trees. When they hatch, the larvae burrow into the soil beneath the trees, going as deep as almost a metre, but generally around 400mm.

This species has a three- to five-year life cycle, most of it spent underground. There the larvae continue to grow, sucking the sap of tree roots for food.

When the weather and other conditions are right, the last stage of growth emerges as a nymph, which heads for the nearest tree and sheds its skin to become an adult.

Then the racket of noise-making begins.

Only the males make noise, clapping their wings against the tree trunk they rest on and hoping to attract a female for breeding.

Other species have a drum-like organ in their abdomen to make a popping noise.

Science notes the cicada as making the loudest noise of any insects, and in some areas the concentration of cicadas is so dense the racket is deafening, measured as the equivalent of a jet taking off.

So what triggers the cicadas to emerge and create their distinctive cicada cacophany?

And is it a sign of the peak of summer, or an early start to the slide into autumn?

Hot, dry weather all seems to play a part, and the cracks that open in sun-baked soil might also help with the insects' emergence from the ground.

Entomologists (those who study insects) in New Zealand believe a key trigger is soil temperature, and have identified 22 degrees as the point when cicadas start to emerge.

And perhaps even the cicadas do not know how long summer will last — so they make the most of it while the going's good!

Cicadas were certainly well-know to early Maori. They recognised around 12 species, identifying them by their sound.

It is recorded Maori called the speech of early European settlers, “te reo kihikihi” or cicada language, apparently because to them it sounded like a harsh chatter compared to their own language.

Maori and Native Americans share an interesting link with cicadas.

Both have tribes who identify cicada with the brightest star, sirius, which is at its highest in the southern summer sky when the nymphs emerge.

One of the Maori gods, Rehua, was the son of Rangi and Papa, and cicadas are believed to be one of the flighted creatures he gave to his brother Tane. Some call them the songbirds of Rehua.