The other main difference between the sexes is the gaster, which is deep and narrow in the male and broad and tipped with an ovipositor in the female.

[4] They lay batches of eggs in the young buds of the oak, injecting venom at the same time.

The eggs hatch and the larvae secrete further substances that encourage plant growth and a globular gall is formed.

The gall provides a nutritious, protective environment and there may be as many as thirty larvae developing inside.

[4] After mating, the females descend to the ground where they make their way into the soil and lay their eggs singly inside the small rootlets of the oak.

Small globular galls appear on the roots and after overwintering as larvae, another generation of wingless agamic females emerge and crawl up the trunk.