Rose gall - a secure domicile.

The above structure is an insect gall. They are formed by various insect species, usually midges (a type of fly) or solitary wasps. Galls can also form from the actions of mites, nematodes, fungi, or bacteria. Gall-forming insects lays an egg on the plant's surface or just inside. It can be on a leaf, twig, or stem depending on the species. Secretions from the mouth of the larva causes the plant tissues to rapidly reproduce and forms a protective case around it that also nourishes the developing insect.

A gall's appearance depends on the species of both plant and insect producing it. The above gall was formed by a wasp (probably Diplolepis polita) on a rose leaf. The spines are produced naturally by the rose but benefit the inner inhabitant by providing extra protection. If you take a sharp knife and cut the gall in half you will find a small grub-like larva inside. The larva typically stays inside the gall until spring when it emerges as an adult to continue the life cycle.

Galls do not generally harm the host plant. Although they can be somewhat unsightly, especially in large numbers, they represent only a mild perturbance to the plant. Some of these insects do, however, have bold and impudent behaviour. You could say that they have gall.

Thanks for reading.     Ericspix     Eric Svendsen