Cicada giants wake to wreck summer nights

If you're arriving at work with serious bags under your eyes there are two likely culprits: hot summer nights and a rowdy chorus of Amphipsalta, the largest native cicada native to New Zealand.

John Perrott, an ecology PhD student at Massey University who is doing the first review of the many studies into New Zealand's cicadas, said it would be no surprise if Amphipsalta were causing sleepless nights.

His research is part of a thesis looking at fungal diseases affecting cicadas. One such fungus acts like something from the movie Alien, erupting from the cicada's chest to bond the insect to the side of a tree.

Amphipsalta is the name given to a genus of three cicada species. Their Latin name means "players on two harps," referring to their ability to make two distinct sounds at once.

Mr Perrott said the males were the noisiest culprits. They use tymbals, circular structures on their undersides between the thorax and abdomen, which are vibrated in the same way as crinkling a can several thousand times a second.

The noise is amplified by hollow cavities behind the tymbals and within the abdomen to attract likely mates - which in turn attracted other males.

The second sound is made by flapping and clicking their wings.

These abilities wouldn't be such a problem, but for one other detail - the noisy Amphipsalta are the only New Zealand cicadas to sing at night.

They are also the last species to emerge from the ground during the summer and, with a lifespan of about a month, may be around for another few weeks.

There has been little study into what event triggers the emergence of the cicadas, but it appears that ground temperatures above 22 degrees C can accelerate their growth. They emerge from the ground during the night as nymphs, crawl to the nearest plant, where they grab hold as their skin hardens and eventually bursts, allowing the adult to back out. If no vertical surface is available this process will not occur and the cicada will die.

The adults tend to gather in larger numbers in modified environments - for example, gardens rather than mature forests - where they lay their eggs and feed on the sap of young plants.

The Amphipsalta then gather in annoying mass choruses to sing.

Mr Perrott said their song had been measured at 120 decibels, 40 decibels over the level considered dangerous to one's hearing.

Such volumes are not surprising given that his studies have shown that up to 190 of the big bugs can emerge from a single square metre of soil - and they don't travel far after they're out.

In terms of biomass, they can reach levels of bug mass per square metre that iare higher than the carrying capacity of a large dairy farm.

Maori and native Americans share an interesting link with cicadas.

Both identify the insects with the Dog Star, Sirius, which is at meridian in the summer sky when the nymphs emerge.

While many people do not realise that New Zealand has more than one type of cicada, Maori recognised 12 types based on their song and identified their arrival with the Dog Star, named Rehua after a forest deity. Cicadas are considered to be his proteges.

Various native American tribes have names for the insects that can be translated as Dog Star cicadas.

Links


NZ Cicada Central