“What are those weird lumps on my creosote bush? Should I cut them off?”

A Question Asked Via Substack

This wonderful question came in from a subscriber to my Substack newsletter. I love Substack because people can ask such anonymous questions and not feel embarrassed, quite unlike other social media. Please sign up for my free newsletter if you haven’t yet – there is a link on the side or bottom of this article.

About those Lumps

First of all, those lumps are called galls. It’s a general the name for those bumps and lumps found on leaves, twigs, stems, and even flowers of various plants. There are a number of very cool insects and some fungi that cause the galls to form. As plant people we tend to be more concerned that galls may be harming the plants they are found on. And a quick answer – no. In most cases, those lumps are not “mumps.” Galls are not a disease.

Word Nerd Shares

Gall comes from the Latin, galla meaning “oak apple,” because circular brown galls are common on oak trees. Meanwhile gallus is Latin for chicken. Indeed, chickens’ scientific name is Gallus gallus, in the order Galliformes.

On a side note, the study of plant galls is called Cecidology, based on the Greek word for plant galls, cecidia.

Galls are Benign

Plant galls are like human warts or benign tumors. They may be unsightly but they do not cause ultimate harm, just tolerable harm. Interestingly, there are some disease fungi that cause benign galls at one stage of their life, but rampant disease in an entirely different plant species at another stage of their life. But I stray from the creosote gall question.

Creosote Galls

While many plant galls are caused by wasps, the creosote galls are caused by tiny fly relatives called midges. Fifteen closely related but different species of midges in fact. Every one of these 15 different species are only found on creosote.

These creosote specialists have partitioned the plant among themselves. Different gall midge species inhabit either leaves, stem tips, young stems, older stems, leaf buds, flower buds, or flowers of creosote bush. Each species induces a uniquely shaped gall but the insects are otherwise morphologically (their forms) very similar and very difficult to tell apart.

Formed by Midges

Wikipedia tells us  “Their life cycle begins when the female oviposits … (deposits an ova or egg) … into the part of the plant which her species prefers. In the case of the creosote midge, she inserts her egg along with a fungal spore from her mycangia” … (a small pocket in her body used to store fungal spores).

The plant responds to this invasion of alien life forms by growing a layer of protective tissue that is the gall. The fungus grows inside the plant tissue, lining the inside of the gall. When the egg hatches the developing larva feeds upon the fungus, not on the creosote itself.

Wikipedia again

“Adult emergence is timed with periods of plant growth associated with winter, spring, or summer rain fall. In contrast to many other groups of plant-feeding insects which form new species through changes to new host plants, new species in the … creosote gall midges … group seems to be a result of colonizing new parts of the same plant plus colonization of new seasons of plant growth.”

Creosote Gall Use

Creosote galls are said to give a different color dye than the leaves.  I shall have to try this.  I have also heard that creosote galls were smoked in ritual by Natives.  More on using creosote on Savor the Southwest.

Plant Gall Variation

Galls come in many shapes, some quite distinctive. Some of the variations are due to the part of the plant they inhabit. Other variations are in color, texture, and so much more. Names include

alder bead – beads on leaves of alder only
beaked spine – looks like spines on leaves
beaked twig – found on twigs, almost like thorns on a rose bush
bullet gall – looks like a series of grey 22 bullets on oak twigs
coral gall – like an undersea coral, even coral colored
cotton candy – so fluffy!
cottonwood – found on twigs where it looks like a puff of cotton
crystalline – very angular
crystalline tube – a tall angular tube

cup and saucer – they named it right!
finger gall – little fingers rising from lower surface of leaves
goats horns – curved like little goats horns
hair silk – tiny lump with a single long strand on top
hair spine – tiny lump on a single long strand
hairy rose gall – like a clump pulled out when your hair gets all knotted, only prettier

But Wait, There’s More

muffin gall – tiny muffins!
mushroom – more mushroom like than the muffins
oak petiole – only on the leaf petioles (stalks) of certain species
pink bow tie – folded into a 3D bow and a rosy pink too
plate – flat and very plate-like
pumpkin gall – orangish and pumpkin shaped, found on leaves
sausage flower gall wasp – uses only the male flower stalks of oak trees
spiked – spike shaped
spiked tube – a very tall tubular spike
spined turban gall – little turban on a stalk
spiny leaf gall – spines out of the tops of leaves
striped pea gall – little striped green peas on leaves

striped volcano gall – striped volcanoes on twigs of oaks
sunburst – a burst of cottony looking growth on leaves
urn – tiny little urns
willow tooth – gives willow leaves teeth!
witches hat gall – small witches hats, not teeth not horns
woolly – like a burst of fuzzy wool found often on roses

The Life of Gall Insects

While the creosote gall midge does not appear to have anything that preys upon it, this is not the case with oak galls in Europe.

Dr. Dr. Amadej Trnkoczy shares this observation with his 2017 photo of an oak gall on the CalPhotos site hosted by UC Berkeley. 0352

“These galls are produced by a gall-wasp (family Cynipidae) Andricus quercustozae. Heavily attacked young downy oaks (Quercus pubescens) were full of them. Generally, galling insects are not considered pests (some are even beneficial and used in biological control for weeds). However, heavy attack may harm young trees as it is evident from the pictures of one of them.

The plant galls develop after the female wasp insect lays egg(s) in a particular plant tissue. The inducement for the gall formation is largely unknown. Experts consider chemical, mechanical, and/or viral triggers.

Anyway, insects demonstrate perfect DNA manipulation of host, which forces him to produce galls. Galls are shelters and food for larvae living in it. After complete metamorphosis larva transforms into adult wasp, which bores a small hole into the outer hard shell of the gall and leaves it.”

Not the Entire Story

Dr. Amadej Trnkoczy continues. “But this is not necessarily the end of the story. Abandoned galls can be later populated by another inquiline species (another insect species that lives commensally … [without causing harm] … in the abandoned galls). Since all galls on my pictures have distinct holes in their outer hard shell, through which grown up wasps abandoned their former `homes,` the white larva inside internal shell (see picture 6a), must belong to another insect species and not to Andricus quercustozae. Which (species) cannot be determined from the pictures only.

Less lucky, Andricus quercustozae larvae can be attacked by certain wasp species in spite of the fact that they reside inside their apparently safe homes. These parasitic wasps lay their eggs inside them from outside of the gall through their hard shell using their long, hardened egg-laying tube (ovipositor). In this case, the Andricus quercustozae larva serves as food for the new inhabitant of the gall. And yet, this is still not the end of the (worst case) story. There exist other insects, which recognize that galls are populated by parasitic insects and lay their eggs into them (hyperparasitoid species).

So, a super-killer kills a killer, who broke in a foreign house and killed the house owner.”

Big Fleas Have Little Fleas

Trnkoczy’s notes remind me of a quote my major professor, B.L. Turner of blessed memory was fond of telling his Beginning Biology students. The quote is based on De Morgan’s variant of a even older Jonathan Swift poem. From DeMorgan’s book A Budget of Paradoxes (1872) we get the saying:

Great fleas have little fleas upon their backs to bite ’em,
And little fleas have lesser fleas, and so ad infinitum.

Galls are Just Fine

Nature filled with many highly complex cycles, and just when we think we might understand a system, we discover new truths. In closing, don’t be alarmed about galls. These bumps and lumps do not cause mumps! They are just part of Nature.

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