Flora and fauna of the Athens County area, and occasionally habitats outside Ohio. Subject matter will consist of both interpretive material and taxonomic issues in plant and animal identification.

Sunday, September 5, 2010

That took a lot of GALL

Galls are irregular growths of plant tissue caused primarily by insects. Insects emit a chemical that causes the plant to grow around the wound, much the same way our skin reacts to a mosquito bite, only more permanent. Wasps, flies, and aphids are most responsible. Some resemble warts, others may be swollen like goiters or tumors.  "It's not a tuma". Oaks in particular are very susceptible. The following is a list of examples, and the insects responsible. There are many more I could have listed, but this post would go on forever.

One of the more common ones is the Oak Apple Gall. Starting out green then turning brown, it is caused by a little wasp, Amphibolips confluenta.

Extremely hard galls encircling oak twigs are also from wasps in the genus Callirhytis.

The same group of wasps can create these elongated galls on oak twigs. These are usually called the Ruptured Twig Gall, from Callirhytis perdens.

Looking like furry caterpillars, these galls on the underside of southern Myrtle Oak are Cynipid Wasps of the genus Andricus.

The orange fuzz balls, common on Oaks, especially White Oak, are the result of a wasp called Acraspis erinacei. The common name for these are Hedge-hog Galls or Wooly Oak Galls.

These orange marsh-mallows are better known as the Strawberry Oak Gall, or Wooly Sower Gall. Created by the wasp Callirhytis seminator, they start out white with red spots, turning this darker color with age.
Whoa, never mind the description. Here it is. Thanks to Lisa Sells (Zen Through A Lens) for noticing I didn't have a pic of this pretty thing as it looks in the spring.

Besides oaks, many other species of plants are subject to gall growths. This is the Spiny Rose Gall created by the wasp Diplolepis bicolor.

Looking like a mass of wet hair, this gall is from Diplolepis rosae, the Mossyrose Gall Wasp. There is a fungus that also creates a similar looking gall.

The Witch-hazel (Hamamelis virginiana) is producing fruit capsules right about now. Later in the fall, these fruits will crack open and look like a hippo opening it's mouth. The witch-hazel will then literally shoot out it's seeds like a cannon. You can even hear a "cracking" sound when they shoot.

Often mistaken for fruit capsules are these structures growing alongside. These are aphid galls.

They differ from the true fruit by having long spines.  These are dark brown because they're a year old. The aphid Hamamelistes spinosus hides inside.

Also on witch-hazel leaves are these Nipple Galls or Coneheads, created by another aphid Hormaphis hamamelidis.

Nipple galls can also be found on Hackberry(Celtis occidentalis). These are formed by an aphid relative known as a Psyllid. Psyllids are 'true' bugs and resemble microscopic cicadas.  This one is Pachypsylla celtidismamma.

Named after the resemblance to a rooster head, these are Cockscomb Galls. Formed by the aphid Colopha ulmicola, they are common on Elms.

Often mistaken for a fruit, this Willow Cone Gall is made by a midge fly Rhabdophaga strobiloides.

Here is a picture of the midge I hatched out of a willow gall.  The pencil point gives you a good idea just how small most of these gall insects are.

Because it grows in open fields, another very commonly seen gall is the Goldenrod Gall. When the plant dies the gall will turn brown.  This ping-pong ball shape is created by a Tephrid Fruit Fly. These are the true fruit flies, different than the Drosophila seen flying around your bananas.
I was lucky enough to hatch one of these out as well. True fruit flies have heavily mottled wing patters like this. A goldenrod gall that is perfectly round is from this fly. A longer, skinnier gall on goldenrod is from a Gelechiid moth.
Look closely at goldenrods, and you may see all the leaves clustered together. This is a Bunch Gall, and is formed by another type of midge fly, Rhopalomyia solidaginis. It is said that this insect is 'species specific', meaning it is only found on Canada Goldenrod.

I want to thank Cassie for commenting on this post. I dug a little deeper in regards to her question. My interpretation of this may be a bit off, but here is what I understand. This fly species has several latin names that are "synonymous".  Perhaps once thought to be different species, they are the same, which means other goldenrods ARE affected. Wrinkled-leaf rugosa, and Tall Goldenrod altissima, are also hosts for this insect.

These Balloon or Pouch galls on Sumac, are actually colonies of insects. The galls may be green or red. An Aphid, Melaphis rhois is responsible.

More aphid galls on Lyonia shrubs in Florida.

Closer to home is this hard Blackberry Knot Gall. The wasp Diastrophus nebulosus lives inside. You can see the exit holes created by the adults as they hatched out. Sometimes these holes are actually from an even tinier wasp that is a parasite on the gall creating species.
Not seen as often is this Colony Gall on blackberry created by aphids.

While not the greatest pictures, these are examples of Stem and Petiole Galls. You can see the effect they have on the new growth of this hickory. Most often these are done by Adelgids.  These are aphid like relatives. People may be more familiar with other wooly adelgids found on the bark of White Pines, or those that have devastated trees like Fir and Hemlock. This species is most likely Phylloxera caryaecaulis.

Another adelgid responsible for defoliating conifers is the Eastern Spruce Gall.  Look for it on Norway and Blue Spruce. Conifer trees react differently than hardwoods to insect defoliators or gall makers.  Because needles do not drop annually, large patches of evergreens may remain bare long after the damager has left.

This is the Cherry Spindle Gall. Spindle galls are most often created by Eriophid Mites. Mites are Arachnids, like Chiggers, and are way too small to photograph.

While a different species, these galls on Elm are also formed by Eriophid mites.

Eriophid mites can be found on just about everything. While not fatal to the plant, anything that works on Poison Ivy can't be all bad. They can be green or red. These are Aculops rhois = A. toxicophagus.

Looking like splattered paint on Sugar Maple, Eriophid mites create a wide diversity of gall types.

The second picture isn't mine, but I couldn't resist putting it up. This is the Maple Leaf Spot gall, and is formed by another Fly Midge Acericecis ocellaris. The first picture may be old remains of Leaf Spot, but if your maple leaves show large black spots on them, that would be Tar Spot, a fungus.

Speaking of which, what appears to be a gall is something called Black Knot. This is a fungus, and if it encircles the entire branch it can girdle it, resulting in death. Black Knot is most often found on fruit trees like cherry and plum. The other galls pictured above rarely ever kill the plant they occur on. You can pull some of them off, or use a mild insecticide to control them.


  1. Your posts are so very informative. Thank you for making them.

  2. Wow, that answered a lot of questions all at once! Thanks so much for sharing your knowledge with us. :)

  3. Do you know of any articles regarding the host specificity of Rhopalomyia solidaginis to Solidago canadensis?

    Or is it a generally accepted norm?

  4. Nice post thank you Chris