Plant Doctor Archive

Serious sandflies

WE have all heard that mosquitos breed in pools of stagnant water, but where do sandflies breed? We have an area in our garden that is always full of sandflies and I get eaten alive! What conditions or plants encourage them?

YOUR query brought back memories of a trip to Scotland last year where I visited the lovely Inverewe Gardens which, among its many collections, has a stunning range of New Zealand native plants. The west coast of Scotland has a problem with midges, which are as pesky as sandflies are here. They were so bad at Inverewe, the gardeners wore special protective headgear so they could keep working in the garden.

New Zealand sandflies are probably at their worst on the west coast of the South Island, but they can be a pest elsewhere, as you have found. Unlike mosquitos, sandflies lay their eggs in clean running water, attaching them to submerged rocks or weeds. After hatching, the larvae remain connected by silken threads and float in the running water, feeding on material that floats by. Once mature, they come to the surface as adult flies and are immediately capable of flying.

Only the females bite, to get the blood they need in order to produce viable eggs. They can travel long distances in their search for blood (10-15km according to one source) and congregate where the humidity is high.

I think it likely your sandflies are coming from a nearby river or stream and perhaps the only measure you could take to dissuade them from visiting your garden is to create open, exposed conditions where there's plenty of fresh air moving around to open up the sheltered, humid spots. Easier said than done - so maybe you'll just have to get used to wearing insect repellent when you do your gardening or put in plants that have a reputation for repelling insects, like artemisias, lavenders, rosemary and lemon-scented pelargonium (Pelargonium citrosum 'Van Leenii').

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.