Mites Meet Maple-Crimson Velvet Erineum Galls


One of the things I like about hiking on wooded trails, is you never know what discoveries await around the next corner. In the case of a hike I took this summer while camping in Washington State, what I found around one such bend was totally new to me.

In fact, it wasn’t until I got home and did a little research, that I was able to identify my find.

Unlike many of my discoveries, this one was out in the open, and almost impossible to miss. Crimson-red patches which shimmered like miniature jewels encrusted many of the low growing maple leaves. Because of the small size of the individual “jewels”, the overall appearance was similar to that of velvet.

The possibilities ran through my mind. Could these be insect eggs? How about fungi? Perhaps it is a slime mold? I wondered if these could be leaf galls, but they were very different than any galls that I was aware of. Besides most leaf galls present themselves on the underside of leaves whereas the ones I found were mainly on the tops of the leaves.

Because I had no access to any reference material or the internet, for the remainder of the weekend I was left to only speculate as to what in the world this ruby matrix could be.

When I got home, this is what I found out about these minute crystal entities:

These growths were maple velvet erineum galls. They are produced as a result of the activities of nearly microscopic eriophyid mites, possibly Eriphyes calaceris.

In general, galls are unusual growths in the leaves, stems, buds or roots of live plants, which are formed by small organisms, and are often triggered by some type of chemical introduced to the plant by the organism. Galls can provide protection from predators, a source of food, shelter from the elements as well as a place for eggs to hatch and develop.

Overwintering female eriophyid mites survive in bark crevices of the host tree. In the spring, they move to the leaves, where they induce production of the galls with their saliva. The mites live and reproduce within the galls through the summer.

This might seem like a textbook case of parasitism, however, in reality, these galls do little damage to well established trees (as is the case with most galls), although individual leaves that are overwhelmed with galls may lose their ability to help to contribute in the process of photosynthesis. So, the type of symbiotic relationship between the mites and the maple, in my opinion is bordering on commensalism, in which one organism benefits from the relationship, and the other is not significantly helped or harmed.

For a look at galls which inhabit the stems of willows, check out Willow Galls.

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12 Responses to Mites Meet Maple-Crimson Velvet Erineum Galls

  1. Wow, it’s really quite beautiful! What a fascinating find! You always discover the most wonderful things on your hikes!


  2. I love the color! It’s interesting that the gall never seems to affect the entire leaf, so infected leaves are more apt to stay on the tree.


  3. Bruce Hagen says:

    Rick, I find galls rather fascinating. They are actually quite common, but most of the time they are drab-looking and rather uninspiring. Occasionally, you run across something spectacular like this mite-induced galling on maple. If you didn’t know any better you might think that someone splattered the leaves with bright red paint. Keep it up, I enjoy reading your writing and images. I’ve spent most of the day editing a paper about the soil food web for publication.


  4. Finn Holding says:

    Fascinating bit of biology Rick, and highly photogenic. I wonder what the biological rationale for that gorgeous colour is?


  5. Max Shields says:

    I have just come across this phenomenon for the first time yesterday. Despite spending lots of time in the woods, this was a new observation for me. Thanks for helping me learn more about it.


  6. Pingback: My First Running Post–Three Things I Can Always Count On | btweenblinks

  7. Pingback: Oak Galls | btweenblinks

  8. Found those crimson galls on my hike in the Olympics last Monday (05/30). Color is so vivid, looks beautiful… Thank you for identifying…..


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