Life cycle

Egg stage

Egg plaques

  • Eggs are laid in masses or plaques about 2cm long on high branches and twigs
  • Females can lay between 100-300 eggs each year
  • Egg plaques are covered with greyish scales and remain on trees during the following autumn and winter.
  • First stage larvae hatch from eggs in April
  • Moths will lay eggs on multiple oak trees

Instar L1 - Mid April

Egg plaques

  • Eggs will hatch just prior to bud burst;
  • Caterpillars are <3cm with black heads and orange bodies;
  • They feed at night and stay in the leaf buds.

Instar L2 - Early May

Egg plaques

  • Caterpillars shed skin as food and temperature increases;
  • The caterpillars remain in the extremities of branches.

Instar L3 - Mid May

Instar 3

  • Caterpillars are now between 10-15mm long;
  • They aggregate in large groups and have started to produce toxic hairs.

Instar L4 - End of May to Mid June

Egg plaques

  • Roughly 20-25mm;
  • They start to form tents, clean and pale in colour;
  • There is an accumulation of shed skin and have approximately 700,000 toxic hairs each.

Instar L5 - June to Mid July

Egg plaques

  • Caterpillars are now much easier to identify at roughly 30mm;
  • Nests are larger and covered in silk and shed skins;
  • There are clear signs of feeding damage.

Instar L6 - Late June to Late July

Instar 5

  • Caterpillars are roughly 35mm in size;
  • Large, dirty nests brown in colour from shed skins, located on trunk and scaffold limbs.



  • At ground level with grass incorporated;
  • Contains a lot of excrement and shed skins;
  • Remains hazardous for many years due to hairs.

Adult Moth

Adult moth

  • Moths start emerging around Mid July and all will have emerged by late September;
  • Moths are nocturnal and live for only three to four days and do not feed;
  • Males emerge before females and can fly up to 20km (12 miles);
  • Females are seldom found more than 500m from their ‘home tree’ and are attracted to the ‘scent’ of oak;
  • Adult moths are not easily distinguishable from some other species.