Last week students in our outdoor classroom sent the picture below, wondering what it was. It's a very logical question, since those...things are growing out of what is obviously a leaf, but no normal leaf has weird miniature mushroom-shapes growing out of it.
|Hackberry Leaf Galls (photo: M. Sherman)|
|Hackberry tree with most leaves already gone for the winter.|
|Three hackberry leaves, two with galls, one without.|
|I broke open this gall, but it was empty. The adult has already emerged from it.|
Hackberries grow well in Middle Tennessee, yet they almost always have hackberry leaf galls damaging their leaves. The trees don't seem overly harmed by the gall psyllids' damage. This is normal parasite behavior. Most parasites don't cause extensive harm to their hosts. They take just a little food from them but not enough to kill them. If a parasite ate too much of its host and killed it, the parasite would be out of food and would die too. Parasites use their hosts in a sustainable manner so that their food source will be available in the future.