▁in ▁Europe . ▁ ▁Description ▁of ▁the ▁gall ▁Ad ult s ▁lay ▁their ▁eggs ▁on ▁various ▁species ▁of ▁o ak , ▁including ▁Hung arian ▁o ak ▁( Qu erc us ▁fra in etto ), ▁ ▁L us itan ian ▁o ak ▁( Qu erc us ▁l us itan ica ), ▁sess ile ▁o ak ▁( Qu erc us ▁pet ra ea ), ▁down y ▁o ak ▁( Qu erc us ▁pub esc ens ), ▁ped un cul ate ▁o ak ▁( Qu erc us ▁ro bur ) ▁and ▁northern ▁red ▁o ak ▁( Qu erc us ▁rub ra ). ▁ ▁Like ▁many ▁o ak ▁gall ▁was ps , ▁there ▁are ▁two ▁gener ations ▁per ▁cycle , ▁with ▁one ▁sexual ▁and ▁one ▁a sex ual , ▁each ▁creating ▁different ▁g alls . ▁The ▁sexual ▁gall ▁is ▁a ▁club - like ▁sw elling ▁at ▁the ▁tip ▁of ▁the ▁shoot . ▁Green ▁at ▁first , ▁later ▁becoming ▁the ▁same ▁colour ▁of ▁the ▁tw ig . ▁The ▁bud s ▁and ▁tw ig ▁develop ▁as ▁normal ▁above ▁the ▁gall , ▁which ▁can ▁pres ist ▁for ▁years , ▁and ▁growth ▁of ▁the ▁tw ig ▁can ▁also ▁continue ▁for ▁years . ▁The ▁female ▁l ays ▁her ▁eggs ▁on ▁a ▁bud , ▁especially ▁on ▁bud s ▁spr out ing ▁sta ight ▁from ▁the ▁tr unk . ▁The ▁a sex ual ▁gall ▁is ▁a ▁small , ▁green , ▁egg - sh aped ▁sw elling ▁in ▁the ▁leaf ▁bra ch ium . ▁It ▁is ▁up ▁to ▁ 6   mm ▁long , ▁often