Nettle leaf gall midge larva, artwork. Cross- section through a stinging nettle leaf (Urtica dioica) and leaf gall. The gall is inhabited by the parasitic larva of the nettle gall midge (Dasineura urticae). The larva emits a chemical which stimulates growth and feeds on the juices and tissue produced inside the gall cavity. A slit in the top of the gall (red) provides an exit point.