Sawflies are a group of insects suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of sawfly in Britain. They have caterpillar-like larvae that feed on plant material and are named after the saw-like egg laying organ used by females to lay eggs in plant material. Adults can come in a range of colours many are black, green orange or striped yellow and black. Most are small (< 1 cm) but some species such as the Birch sawfly (Cimbex femoratus) can be over 2 cm long. Several species can be found in gardens and are part of the biodiversity a healthy garden will support. More information can be found at The Sawflies of Britain and Ireland webpages.

Aruncus sawfly has pale green caterpillar-like larva that reach 20 mm in length and eat the leaves of Aruncus plants. The adult is a winged insect, 5-6 mm long with a yellowish abdomen and darker head and thorax. The wings are clear with brown veination.

Aruncus sawfly larvae feed in groups so defoliation can occur quickly. Keep vigilant for early signs from May onwards:

• Pale green caterpillar-like larvae with yellowish brown heads and up to 2 cm long
• Leaves can be reduced to a network of the larger leaf veins, plants often recover but repeated defoliation can affect the vigour host plants

Larvae can be found from May (first generation), with a second generation in July and August and a third generation in September.

Sawflies are a part the biodiversity a healthy garden supports.

• Where possible tolerate populations of aruncus sawfly, plants often recover from defoliation and may not be affected every year
• Encourage predators and other natural enemies of sawfly in the garden, such as birds, wasps and ground beetles
• Check plants regularly from early May for the presence of larvae to prevent a damaging population developing
• Remove by hand if required and where practical

Aruncus sawfly defoliates goat's beard (Aruncus dioicus), a plant that was formerly included in the genus Spiraea, so this insect is sometimes known as the spiraea sawfly. It occurs in gardens throughout Britain. 

The adult sawfly is 5-6 mm long and has a black head and thorax with a yellow abdomen marked with dark bars on the dorsal surface. Larvae overwinter in the soil and, after pupation, adults emerge in May and lay eggs that hatch after about 7 days. Two or three generations of pale green larvae with brown heads feed gregariously on the foliage during the summer months, reducing the leaves to a network of the larger leaf veins. The pupal stage takes place within a silk cocoon in the soil.

This is a species that reproduces asexually and all the adults are female.