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Geranium sawfly is an insect closely related to wasps, but lacks a distinctive 'wasp-waist'. Adults are black, slender and sleek in their appearance, feeding solely on nectar and pollen. The larvae resemble caterpillars, and like caterpillars, can cause substantial damage to plant foliage. These larvae are grey-green with brown heads, who feed solely on the leaves of geranium.
Caterpillars leave holes in Geranium plants.
Adult sawfly feeds solely on pollen and nectar, making them pollinators.
Adults: Adults look like slender, thin, black flies (1cm). You might see these insects buzzing about flowers during spring blooms. Larvae: The larvae are pale green-grey. They are brown-headed and only reach about 1.2cm. They will drop from leaves if disturbed, so the gardener rarely spots them.
Holes in the leaves of geranium may be evident during summer months. Young plants may lose vigour.
Larvae can be removed by hand and disposed of, or fed to the birds. Although damage can be unsightly, it's been advised to try and tolerate these insects if you can. They can provide wider ecosystem services as adults, so toxic treatments should be avoided. Attract natural garden predators into the garden by providing spots of cover. Wild patches and strips of native wildflower/ grass can provide cover for predatory insects. Climbing plants such as ivy is excellent habitat for small songbirds.
You can spray plants with pesticides if you have an infestation that is too large to remove by hand. Please consult with your local garden centre, research and read labels carefully before any chemicals are applied to plants. Do not apply any persistent chemicals when plants are in flower, as these chemicals can be detrimental to pollinating insects.