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Birch Sawfly

Cimbex femoratus

Birch Sawfly

A close up image of a Cimbex femoratus birch sawfly on a metal surface
Cimbex femoratus by Pistiäinen (CC BY-SA 3.0)
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Cimbex femoratus, or Birch Sawfly, is one of the largest in Europe and the UK. They create a loud, droning buzz while in flight! Sawflies are close relatives of the wasps and bees; however, they can't sting. The females have saw-like appendages used to cut the bark of trees, in which they lay their eggs. Adults are nectar feeders, whereas the larvae feed on the leaves of SIlver Birch, favouring most habitats that contain the tree. The larvae hatch in the spring and feed until large enough. They pupate and emerge as adults in late summer.
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Traits

Large, established trees can tolerate infestations.
May damage smaller birch plants.

Appearance

Adults: Mature insects grow between 1.5-2.5cm (0.7–0.9 in). They possess distinctive clear wings with smoky brown borders and venation. They have black and shiny thorax and a length abdominal section. The abdomen may possess a white and red band, which appears more distinctive in males. The antennae are mostly black with orange-yellow bulbous tips. Larvae: The larvae are extremely similar to caterpillars! They're pale mint green and will grow roughly 5cm in length. They have a sky blue strip that runs the length of the back, and black dots that run down each side of the body. Eggs: They're impossible to find because they're laid inside the bark!

Symptoms

Caterpillar-larvae may be found feeding on Birch. Defoliation is mild. Won't do long lasting damage.

Activity

Diurnal

Personality

Order

Hymenoptera

Family

Cimbicidae

Metamorphosis

Complete

Distribution

Europe and Siberia

Biological treatment

You should try to tolerate these insects in the garden if you can. The caterpillars are solitary, so they won't defoliate the tree that much. The larvae of many insects will be predated by parasitic or social wasps, birds and bats. If they're on your prized silver birch, or your tree if young, remove caterpillars by hand.

Attracts

Birch

Betula spp.

A weeping green Betula pendula 'Tristis' plant

Weeping Birch

Betula pendula 'Tristis'

Common Silver Birch

Betula pendula

Repels

Bats, birds, wasps.
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