The Gall of It

There’s a tree in the gully near our orchard.

Last February, when several plants of the myrtle family (Myrtaceae) were in bloom with their small white flowers and many stamens, this tree, too, was in bloom with its small white flowers and many stamens.

Like the other representatives of the myrtle family, the leaves are simple and opposite, and with my hand lens I can persuade myself that the leaves have small translucent dots, called punctations, like all members of the myrtle family.

However, … I have yet to identify this tree and I’m not even 100% confident of those punctations. I recently saw some things in the tree, though, that may help, in the end, to identify it. These things are galls:

Galls provide both a home and food for developing insect larvae inside (one article about them was called To Have your House… and Eat it Too). Insects that cause plants to form galls are called gallers or gall-inducing insects. Many gallers are flies or wasps. Until recently, it was believed that there were about 13,000 species of gallers, mostly known from the northern hemisphere, but a survey published in 2007 estimated there may be ten times that amount – 133,000 species, with the estimates ranging from 21,000 to 211,000. There are some wonderful varieties of galls, several of which may be seen at What’s That Bug?

After the adult deposits an egg on the plant, the developing larva induces the plant to produce an abnormal growth. This growth becomes the larvae’s home and food supply. Unless a plant is infested with galls, the plant does not seem to be harmed by galls. Still, the plant does not derive any benefit from the gall and so gallers are considered parasites on the plants. Incidentally, not all galls are induced by insects – galls may be induced by bacteria, viruses, fungi, or nematode worms.

The reason the galls in these pictures may eventually help me identify my tree is that each galler tends to deposit its eggs on only one species of plant. So…if I were to identify the gall, I’d no doubt be able to identify the plant. Whether this has made my life easier or whether it has simply doubled my difficulties remains to be seen.

Update: The kind folks at What’s That Bug? have posted an image of my gall in the hopes that someone might recognize it. They did point out that this one is a twig gall, not a leaf gall, which is unusual. That’s a start.