Longhorn beetles

Cerambyx cerdo and Cerambyx welensii

1. Identification

• Common name: Capricorn beetles
• Scientific name: Cerambyx cerdo L. and Cerambyx welensii Küster
• Order: Coleoptera
• Family: Cerambycidae

2. Pest description

• Adults: Large longhorn beetles, 25–55 mm; elongated body, dark brown to black; very long antennae, which may exceed the length of the body; robust and slightly shiny elytra.
• Larvae: White, cylindrical, with a brown head; reach large sizes (up to 70 mm); bore deep galleries in the wood.
• Pupae: Formed inside the wood, in oval pupal chambers.
• Eggs: Laid in cracks of the bark or in weakened areas of the trunk.

3. Main hosts

• Oak, especially cork oak and holm oak.
• Other Quercus species, including Q. robur, Q. faginea and Q. pyrenaica.
• They may also occur on chestnut and occasionally on other large broadleaved trees.

4. Symptoms and damage

• Wide perforations in the bark and expulsion of coarse frass.
• Deep galleries in the wood, compromising the structure of the tree.
• Longitudinal cracks in the trunk due to larval activity.
• Progressive decline of the crown, with dry branches and loss of vigour.
• Greater susceptibility to fungal infections and other secondary agents.
• In severe attacks, they can cause the death of the tree or make it structurally unstable.
• Although C. cerdo is a protected species in several European regions, populations of C. welensii and, locally, of C. cerdo, may behave as a pest in Mediterranean montados, especially in weakened trees.

5. Biological cycle

• Multiannual cycle, generally 2–4 years, depending on environmental conditions.
• Adults emerge in late spring and summer.
• Egg-laying in cracks of the bark; larvae bore deep galleries in the wood over several years.
• Pupation inside the wood; adults emerge through characteristic oval holes.
• Development favoured by weakened, aged trees or those subject to water stress.

6. Monitoring

• Observation of oval emergence holes and expulsion of frass.
• Inspection of trunks with longitudinal cracks or areas of necrosis.
• Assessment of the crown to detect drying of branches and loss of vigour.
• Reinforced monitoring in cork and holm oak montados, especially in older trees.
• Pheromone traps and/or attractants may be used for detection and population tracking.

7. Management measures

• Cultural: Removal of heavily affected trees; improvement of stand vitality; avoiding injuries to the trunk.
• Preventive: Adequate density management; reduction of water stress; maintenance of healthy soils.
• Integrated protection: Regular monitoring; intervention only when necessary; practices that reduce the attractiveness of weakened trees; attention to the legal framework, given that C. cerdo is protected by European legislation (Habitats Directive – Annex II and IV), even when local populations exhibit pest behaviour.

Bibliographic references

• EPPO Global Database – Cerambyx cerdo and Cerambyx welensii.
• CABI Invasive Species Compendium – Cerambyx spp.
• Torres‑Vila, L. M. et al. (2017). Biology and management of Cerambyx species in Mediterranean oak systems.
• European Commission – Habitats Directive (92/43/EEC).