Help for monarch butterflies

Christchurch’s monarch butterfly colonies are about to get a lifeline.

Entire monarch butterfly colonies were all but wiped out in two city parks last winter and rats are thought to be the number one culprit.

In April last year, Abberley Park in St Albans was home to about 700 butterflies but by late August eight remained.

Burnside Park had 400 in autumn last year and by the end of winter four remained.

The Christchurch City Council will spend $1500 buying and installing rat and predator-proof steel bands around trees in both parks. A report, discussed at the council’s social, community development and housing committee yesterday, said there was no scientific evidence black rats were killing the butterflies but anecdotal evidence and expert opinion suggested rats were the most likely scenario.

The steel bands were considered a cost-effective solution. They would cost about $180 a tree.

Butterfly specialist Vicky Steele, who has been lobbying the council to do more to prevent the destruction of butterflies, was pleased by the council’s plan.

‘‘The butterflies are not just dissolving and their wings falling off, they are being eaten.’’

Butterfly numbers usually reduced throughout winter, as they succumb to the weather or lack of food, but not to this level.

In 2015, the butterfly mortality rate at Abberley and Burnside Parks was 4 per cent.

Steele, who has studied butterflies for 20 years, knows how many have been killed because she regularly picks up their wings from the base of the trees.

The wings were often all that were left.

Monarch butterflies usually live for about six weeks in the summer. In autumn they enter a type of reproductive hibernation and spend the winter on evergreen trees where they cluster together and look for food during the day.