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Great spruce bark beetle (Dendroctonus micans)

The great spruce bark beetle damages spruce trees by tunnelling into the bark. This pest was accidentally introduced into the UK in 1982 and now has become established in Western England, Wales and Southern Scotland.

Larvae bore feeding galleries under the bark of the tree.

Credit: Forestry Commission

Resin bleeds are a sign of the tree's distress.

Credit: Suzanne Sancisi Frey / Forest Research

The tree produces resin as a response to adult females boring into the tree to lay eggs.

Credit: Suzanne Sancisi Frey / Forest Research

The beetles originate from Siberia and spread through Europe.

Credit: Forestry Commission

So far they have affected parts of western Britain.

Credit: Martin Jukes / Forest Research

The larvae's feeding galleries impact the tree's ability to transport water and nutrients.

Credit: Isobel Cameron / Forestry Commission

Quick facts

Common name: great spruce bark beetle

Scientific name: Dendroctonus micans

What does it affect?: Sitka spruce, Norway spruce, oriental spruce

Areas affected so far: UK excluding Northern Ireland and Western Scotland

Origin: Siberia

What does great spruce bark beetle damage look like?

Symptoms include:

  • Resin tubes which are produced when the female beetle bores into the tree to lay her eggs. In response, the tree produces a strong resin flow to try to protect itself. These can be a range of colours from white, purple, and brown.
  • Feeding galleries, where the larvae bore tunnels, often occur beneath the bark in areas close to resin tubes. You can find these by listening for a hollow sound when tapping on the bark. In heavily infested trees the bark will fall away to expose these galleries.
  • Exit holes made by adult beetles. A single exit hole (approximately 2–3.5 mm wide) can be used by a number of adults. Powdery frass is also ejected through the emergence holes and can collect at the base of a tree.

What is the great spruce bark beetle?

The great spruce bark beetle is one of the largest bark beetles. Adults are 6-8mm long and up to 3mm wide. In the UK, the beetle has a long life cycle, ranging from 12 to 18 months. It begins when adult beetles tunnel into the bark of living trees to lay eggs. When they hatch the larvae excavate feeding tunnels and galleries.

What happens to the tree?

If the infestation gets too large and the stem becomes girdled, a wound which means the tree can no longer transport energy from photosynthesis or water from the roots, everything above the wound will ultimately die. This is particularly harmful if the main trunk is girdled.

Where has the great spruce bark beetle impacted?

This non-native beetle now affects trees in western England, Wales and southern Scotland. It’s widespread across Europe and Asia.

Credit: Martin Jukes / Forest Research

When did the great spruce bark beetle get here and how?

The beetle was first discovered in the UK in 1982 although evidence has now been found that it could have been here as early as 1973, though we don’t know how it arrived. In 1996 an outbreak site was discovered in Kent leading to the realisation that its range had spread from the west of the country.

One way it might have made its way to the UK is through the movement of untreated wood from infested sites in Europe and Asia. The larvae can live concealed inside infested wood and remain undetected until after transportation.

What impact will the great spruce bark beetle have?

At temperatures of between 12°C and 20°C adult beetles move within and between trees by crawling, but when temperatures reach 22.5°C they are able to fly. Increasing temperatures through climate change might lead to increased spread of this beetle in the UK.

It causes significant dieback of trees but its effects can be made worse when other stress factors, like drought, are affecting the trees. It can take a few years of sustained attack to kill trees.

That said, this pest is currently kept under control using an introduced predatory beetle from its home range of Siberia called Rhizophagus grandis. This form of biological control has produced great results and is even effective if there are just a few great spruce bark beetles in a woodland. The Rhizophagus grandis will find them!

In the UK, an area in the west of Scotland has now been designated as a pest free area. It is regularly surveyed by Scottish Forestry as part of its ongoing programme.

What are we doing about it?

To combat pests and diseases like the great spruce bark beetle we have:

  • Developed a UK and Ireland Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK. 
  • Lobbied the Government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health Citizen Science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.

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We are fighting back against pests and diseases. Find out what we're doing to prevent the spread and protect the UK’s trees. 

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What to do if you spot the great spruce bark beetle

If you think you have seen the signs and symptoms of this pest please report it to the plant health authorities via TreeAlert if you are in Britain or TreeCheck if you are in Northern Ireland.

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