The geranium bronze or brun des pélargoniums in French (Cacyreus marshalli), is a butterfly in the family Lycaenidae.

The butterfly was first introduced to Europe in the late 20th century, where it has quickly spread to many southern and eastern European regions.

Currently, efforts are being made to contain the spread of the geranium bronze butterflies as well as to determine the most effective pesticide for the species.

[4] The male and female are similar in appearance.The geranium bronze was first recorded in regions of South Africa, including KwaZulu-Natal and the Cape Provinces, as well as in neighbouring countries such as Eswatini, Botswana, Zimbabwe, Lesotho, and Mozambique.

[6] After being recorded in England, a colony of geranium bronze was soon found in Mallorca in 1990, and has since spread to most of the regions in southern Europe.

In 1996, the geranium bronze butterfly was first recorded in Rome, Italy, and rapidly spread along the Adriatic and Tyrrhenian coastal areas before extending inland.

[7] The geranium bronze butterfly now has established colonies in Belgium, Germany, the Netherlands, Italy, France, Greece, Malta, Spain, Portugal, southern Switzerland, Slovenia, Croatia, and the French Mediterranean.

[6] Geranium bronze eggs are small with a slight green color that turns white then brown or light-yellow before the larva hatches.

[4] The geranium bronze butterfly has not been reported as a pest in its native home and surrounding South African regions.

[8] If geranium bronze numbers in Italy and other regions of Europe continue to rise, it is possible that they will become a larger threat for not only the native flora, but also for local biodiversity.

In countries like Spain, the Geranium plant species are highly valued in Spanish homes as ornaments.

Contact pesticides were found to have no effect on the butterfly, because the larva spends the majority of its life within the plant, along with other endophytic habits.

[2] In addition to Bacillus thuringiensis, the insecticides diflubenzuron, flufenoxuron, hexaflumuron, lamda-cyhalothrin, alphamethrin and benfuracarb are also effective.