The castor oil plant is a species of flowering plant in the spurge family. It is a native of East Africa and India but has been introduced to many parts of the world, including Malta. It prefers warm countries but it can also be grown in temperate regions as an annual plant.

It is an invasive species locally and grows mostly in valleys to the detriment of indigenous species. It produces large seeds that can spread by means of flowing water and it can easily spread to new sites especially along water courses.

In the mid-19th century there were a number of attempts to start a silk production industry in the Maltese islands. One attempt was to produce silk produced by the Eria silkworm, a species of moth native to India. The caterpillars of this moth feed on the leaves of the castor oil plant.

The first eggs arrived in Malta in 1853 – they were the first of this species ever to arrive in Europe. They were taken to San Anton Gardens where hundreds hatched successfully. The caterpillars started dying until it was realised that the weather was too cold. The room where they were being kept had to be kept warm until March.

With the first batch of silkworms the governor produced enough silk for a pair of stockings and some lacework. The project was deemed successful and the moths laid so many eggs that a large quantity was sent to France and Algeria.

In 1854 the Land Revenue Department issued a call for applications for persons who were interested in rearing the Eria silkworm in Malta or in sending it to other countries. The applicants had to ensure that they had the castor oil plant growing on their lands.

After its initial success the project, however, failed because of inbreeding of the caterpillars, which became weak and lost their vigour. But the castor oil plants remained here, choking the vegetation in valleys and other natural areas.

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