Gall or nest?
August 3, 2009
Hi guys!
I absolutely love your site, and tell all my friends about it! I found a very alien object clinging to a creosote bush behind my house, in Tucson AZ. It is a leafy sphere, about the size of a quarter. The leaves (which don’t look anything like those the creosote leaves) are arranged in whirls, like a grassy daisy, and there is a tiny hole in the center of each. Coming out of each hole are discarded exoskeletons, like those of the grain moth larvae you find in boxes of rice and pancake mix. They are probably only 4 or 5mm long. There is also a bit of silk strewn around the whole thing, which gives it a dewy, sticky look, but I haven’t touched it because I don’t want to be impregnated by some alien insectoid race. What kind of bug could construct such a crazy looking (and beautiful) nest? Or is it a gall of some sort? I am so very curious…
Thanks for your help!
Emily Rush
Tucson, Arizona, USA

Creosote Gall

Creosote Gall

Creosote gall
August 3, 2009
Me again. After writing to you, I decided to google “creosote gall”. Don’t know why I didn’t do that first, I guess I was just excited to send you a pic of something you might not have seen before. Apparently my mystery alien sphere IS a gall, caused by, wonder of wonders, a creosote gall midge! I couldn’t find a picture of one though. Any help in this area?
Thanks again!
Emily Rush
Tucson, Arizona, USA

Hi Emily,
Thanks for sending us your photo of a Creosote Gall and doing the subsequent research.  BugGuide has images of the Creosote Gall filed under the species Asphondylia auripila with the information:  “Larvae form galls in creosote bush (Larrea tridentata),”
but if you go to the genus Asphondylia and browse, you will see some images of related Midges that probably look very similar to the Creosote Gall Midge. The only species on BugGuide with images of adults is Asphondylia solidanginis. Species in the same genus often have visual similarities and an expert is required to differentiate one from another.  Unlike the Oak Gall we just posted which was formed by a small wasp, the Creosote Gall is formed by a Midge that is in the order Diptera and is classified with the flies.  The Creosote Gall is a deformation of the plant with the leaves and stems stunted to form the Gall.  If you follow the taxonomy on BugGuide back to the Family Cecidomyiidae, you start to get a bit more information, including:  “Minute, delicate flies with long legs and usually relatively long antennae, and with reduced wing venation” and “more than 1,200 species in 170 genera in North America.” There are images of many different species on the Cicidomyiidae page of the Forestry Images website.  Some of the members of the family include the Skeletonweed Gall Midge and the St. John’s Wart Midge.  Those should give you some idea of what the Creosote Gall Midge looks like.  Again, thanks for sending us your photo.

Thanks Daniel!
I hope I can catch a midge in action. By the way, the root borer you posted is a Palo Verde beetle (Derobrachus geminatus). We have lot’s of them in Tucson- they’re HUGE, and they’re really active right now, during the monsoon. I like their fancy spiked collars! Here’s another!

3 Responses to Creosote Gall

  1. Aariq says:

    I’m loving the recent gall posts. To me, galls are one of the most beautiful things in the natural world. They are often outwardly beautiful, but even when they are not, the interaction between an insect and a plant that goes on to bulid such a structure is surely one of the most intimate and beautiful interactions in the world. So thanks from a huge gall fan.

    • bugman says:

      We wish we had time to post more about the relationship between insects and the plants that they form Galls upon, but much of that is already posted in our archives.

  2. Richard Lohmeyer says:

    How do I treat for Creosole Gall. I have several Croesole bushes dying. What can I use to treat the bushes. Please help me. Thanks

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