One of my students this semester wanted to work with parasites for his semester ecology project and we discussed some ideas. I told him about mistletoe in Arizona and the gall forming insects that you can find all over the desert. This is my favorite gall here:
Creosote gall! The female creosote gall midge, a type of fly, lays her eggs in a branch of a creosote bush. The presence of the egg/developing larva induces the plant to grow in a strange new way, covering the helpless maggot with the leafy ball you see here. The fly then develops safely inside the plant until it emerges as an adult. Sadly, my student chose not to work with the galls and will be working with the mistletoe instead, but I did end up with one of the galls to photograph. Aren’t they beautiful?