Creosote Bush Gall

Asphondylia auripila Midge gall on a creosote bush. This one’s dry and brown – indicating that this is an old gall.

Here’s a photo of a neat-looking gall on a Creosote Bush (Larrea tridentata).

A gall is tissue that a plant grows in response to certain types of physical or chemical irritation. Many insects and other creatures have figured out how to take advantage of a plant’s gall-forming response. The insects convince the plant to grow a gall that serves the insect as shelter, and sometimes as a source of food.

In this case, the gall was created at the behest of a small (roughly 5 millimeter long) midge, Asphondylia auripila.

The cycle began when an adult Asphondylia auripila laid her eggs on the Creosote. Either the adult or the larvae - I’m not sure which - released chemicals into the Creosote which irritated the plant in just the right way, encouraging the Creosote to built a home for the midge larvae.

The midges are architects of irritation, if you will.

I took the photo back in May of 2001, in Maricopa County, Arizona. This gall was roughly an inch in diameter. It was dry, brown and crunchy, an old gall, perhaps from the previous year. Younger, fresher versions of these galls are shaped similarly, but are soft and they are the green color of Creosote leaves.

Interestingly, this gall is actually made from a number of smaller sub-galls clustered together, each containing another larva. Russo (2021) states that the large, round gall is actually:

“…composed of hundreds of thin, 10-mm-long bracts arranged in multiple, small rosette patterns. The bracts arise from each of the individual club-shaped to pyramidal galls comprising the larger gall mass. These individual galls measure 7mm high by 3mm wide at the base.”

It reminds me of the sub-units of composite flowers, the way that the ‘flower’ of a daisy is comprised of multiple ‘sub-flower’ units. I’m assuming that when a female midge lays her eggs, she lays a number of them close together, and together the larva form their sub-galls, which merge into the larger gall structure we see. I wonder if there is an advantage to the midges in having the gall sub-units cluster this way, forming a larger, round structure?

There are at least sixteen other Creosote gall-forming midges that are very closely related to Asphondylia auripila. Even though they are different species, they are so closely related that all of them are referred to as the “Asphondylia auripila group”.

The adult midges in the Asphondylia auripila group look similar to each other, but their galls look quite different, and are in different locations on the plant. Some are on the twigs and stems, others are on the leaves, still others are on the flowers, etc.

According to Joy (2007), most of these Creosote Bush Asphondylia midge species originated without switching host plants away from Creosote Bush. So the individual species didn’t come to the Creosote Bush directly from, for example, a Salt bush.

Rather, the newer species of Asphondylia also originated on Creosote Bush, deriving from the original Creosote Bush-galling Asphondylia species. They did this by changing their preferred gall location on the Creosote Bush - that is, they changed gall location, not plant species. For example, rather than preferring to form galls on the stems, a certain population may have started creating galls on the leaves. That means that different physical and behavioral traits were selectively advantaged in the two populations of Asphondylia midge - and they drifted apart genetically until they could no longer be considered the same species.

On a different topic - I’ve found a number of references to specifically the Seri people smoking these galls(!) - see the “Sources” below for a partial list. I’ve been curious about why the Seri might smoke them - whether it was for medicinal, ceremonial or recreational purposes.

A few of the references I found said that the Seri smoked the galls “like tobacco.” I’m not sure of the mechanics of that, either. I’m assuming that they dried the younger, green galls, but it’s possible they smoked the older, dried galls, like the one in my picture.

Creosote Bush itself had many medical uses amongst indigenous peoples in the Southwest.. But I’ve not found mention of other groups of people smoking the galls, just the Seri. Which is odd, given how geographically widespread and common both Creosote Bush and Asphondylia auripila galls are.

I’m quite curious about this, so if you happen to know more, please send me an email or leave a comment.

Sources:

Bugguide.net is, again, an invaluable source of information. Their page on Asphondylia auripila galls is here: https://bugguide.net/node/view/249532. What I like the most about them, though, is that they have links to the various sources and keys. It’s astonishingly valuable. That’s how I found a copy of Raymond Gagne’s paper, below, a link on the Bugguide.net website.

Gagne, Raymon J. and Waring, Gwendoly L. 1990. The Asphondylia (Cecidomyiidae: Diptera) of Creosote Bush (Larrea tridentata) in North America. Proceedings of the Entomological Society of Washington. 92(4), 1990, pp 649-671. Link for the paper here.

Gallformers.com has a good page on this gall here: https://gallformers.com/gall/1798

Joy, Jeffrey B. and Crespi, Bernard J. Adaptive radiation of gall-inducing insects within a single host-plant species. Evolution Vol 61, Issue 4, p. 784-795. https://doi.org/10.1111/j.1558-5646.2007.00069.x .

Russo, Ronald A. 2021. Plant Galls of the Western United States (Princeton Field Guides, 142). Princeton University Press. ISBN-10: 0691205760. Again! What a fabulous book this.

Wikipedia’s page entry for “Creosote Gall Midge” has a nice discussion of the diversity of gall-forming midges in the Asphondylia auripila group that form galls on Creosote.

References to the Seri people smoking these galls: