MetService finds bugs in its weather radar

MICHAEL FIELD
Last updated 10:34 23/02/2013
Bigs
NO RAIN SHADOW: MetService's radar showed a Taranaki-sized patch of precipitation - even though there was no rain. It suspects the echo was an insect swarm.

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A vast swarm of bugs that covered much of the northern half of the North Island was so large it was recorded on the MetService weather radar.

MetService initially did not know what the disturbance was but finally identified it as flying insects.

The exact identity of the bug had entomologists similarly puzzled, although an Aussie pest is topping the list of suspects.

There is a strong suspicion that it is an unwanted Australian heading home - ironically perhaps because our drought conditions have proved too much.

One expert has said it is probably the Tasmanian grass grub.

MetService's Peter Kreft said the bugs began swarming over the Waikato region around 9pm on Thursday.

"They were pushed by the south- easterly wind north toward Auckland," he said.

By around 7am yesterday the massive swarm was out over the Tasman Sea, west of Auckland.

"We see this from time to time, but this one is a very good example of it."

Stephen Pawson of Scion, a Crown research institute, said at a guess the timings favoured the Tasmanian grass grub (aphodius tasmaniae), an introduced agricultural pest. "It is the right time of year for them to emerge. They can come out in massive numbers," he said.

"Its the right time of year, right time of day and to a degree - and I am not an expert on Tasmanian grass grub - but we've had drier conditions."

A similar emergence had occurred in Canterbury some years ago - and again between Christchurch and Ashburton on the night of January 23.

However, he said such swarms seldom reached Australia, dying over the Tasman and washing ashore.

He warned west coast beaches around Auckland could see thousands come ashore.

Hort Research said grass grubs are 10-12mm long and they make tunnels in the soil in which they stay during the day.

Its larvae feed on the foliage of grasses, clovers and lucerne in pastures, home gardens and recreational grassland and turf.

"Tasmanian grass grubs live in light soils in the coastal areas of Canterbury (particularly), Marlborough, Auckland, and Northland. Infestations tend not to cover wide areas, but are patchy and severe over relatively small areas of up to one hectare," Hort Research said.

"Dense swarms aggregating around street or shop lamps in urban areas are common."

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- The Dominion Post

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