Ultracoelostoma assimile (Maskell, 1890)

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Common name: Sooty beech scale insect

Order: Hemiptera  Family: Coelostomidiidae

Size: up to 5 mm

These tiny insects live within the bark of native beech trees (Nothofagus spp.) and produce large amounts of honeydew, a sweet syrup that is a critical food source for numerous birds, insects and fungi. The scale insects themselves are hard to spot as they look like small, flattened discs with their mouthparts buried inside the tree. However, their presence is given away by the long, thin anal tubes which extend out from the bark. At the tip of the tubes are little droplets of honeydew that the scale insect expels after sucking the sap from the tree. These droplets are produced because the scale insect has to drink a lot of tree sap to get all their nutritional requirements, and the sap is made up of a lot of excess sugar that the scale insect does not need.

For birds such as tūī and bellbirds the honeydew is particularly important in winter months when other nectar sources are harder to come by. Also, in areas of forest where there are many scale insects and lots of honeydew, the beech trees can be covered in a type of fungus commonly known as sooty mould. This black mould can cover the trees and in itself is an important food source for insects such as beetles and moths.

Unfortunately the honeydew also attracts huge numbers of introduced wasps, which can carry off up to 90% of the honeydew available meaning there is very little left for the native birds, insects and fungi that rely on the scale insects for food.