Eriococcus coriaceus is a common pest of Eucalyptus trees, particularly E.globulus in plantations. The oval sac covers the body of the wingless female. The female lays hundreds of eggs within the sac. There is always an opening left at the end to allow nymphs to leave the capsule. The honeydew exuded by the insects often causes a black sooty mould to grow on the leaves which can affect photosynthesis. There are many natural predators and parasites of this species. These include ladybird beetles and parasitic wasps.
CSIRO, 1990. Insects of Australia, Volume 1: A Textbook for Students and Research Workers. 2nd Edition. Melbourne University Publishing.
Forest and Timber insects of Australia No 22. https://www.scionresearch.com/__data/assets/pdf_file/0018/3951/Ent22Eriococcuscoriaceus.pdf Accessed September 18, 2016