Scale Insects

scale insects on leaves

Scale insects (Order Homoptera/Hemiptera, Family Coccidae) get their common name from the covers (scales) the juveniles produce to protect themselves. There are generally two types of scale - 'soft' and 'armoured' - but the size and shape of the scales varies according to species. Soft scales are typically formed from honeydew excreted by the insect, similar to lerps, while armoured scales are formed from the waxy filaments that the insect secretes as it rotates its body in a circular pattern.

In most species the female will live within the scale for the entire life cycle, often remaining both legless and wingless. Males live under their scale cover until maturity, when they emerge as winged adults. Mating or fertilisation takes place through the scale cover of the female. In some species of soft scale insects, fertilisation is not necessary as the female is capable of reproducing parthenogenetically (i.e. reproducing without requiring a mate).

Scale insects feed by sucking sap from plant tissue and are considered pests. They weaken the host plant by reducing its food supply and, like lerps, the honeydew based scales attract sooty moulds which use it as a food source. The sooty moulds blacken leaf tissue, reducing the photosynthetic capacity of the leaves and when infestation is severe, this may lead to retarded growth and defoliation.