Naturespeak A naturalist's view of the world

February 28, 2010

Gnat’s Not a Pine Cone

Filed under: Uncategorized — wykes @ 9:10 pm

So, you’re looking at a willow shrub and you see a bunch of pine cones stuck onto some of the branches. You say to yourself, “That’s a willow shrub, so those can’t be pine cones unless somebody got all decorative-like and deliberately put them there.” You turn around and realize that you are indeed talking to yourself and, out of self respect, you carry on the rest of the conversation internally. “Who would do that? This place is miles from anywhere. However, if Martha Stewart was in the neighborhood she would do such a thing.”  The conversation betwixt the left and right brain continues.  “Look at them, those aren’t cones,” you continue silently, “they’re all fuzzy.” “Well, maybe them is cones and they is rotten and all covered with fungus.” “No, Martha Stewart never uses old cones, she…”  “You need to shut up.” “No, you shut up.”

Such a grammatically incorrect conversation could happen. Therefore, I feel it is my public duty to reveal the truth behind those willow “pine cones” as a preventive measure. I’d hate to see you lying unconscious in the snow with self-inflicted fist marks on your face. This thing is so easily solved. Martha Stewart, you see, has never walked any of the loop trails at Crosswinds Marsh where these pictures were taken. End of story.

Now, for those of you who need more, I will continue with a more, a much better explanation. Those cone-like structures found on scrub willows are called Pine Cone Willow Galls. They are growths caused by tiny gnats. The story began last spring when a long-legged gnat fly called Rhabdophaga strobiloides (“stem-eater within a pine cone home”) laid her egg on the terminal (end) bud of a new willow shoot. The insect egg, and the resulting larvae, triggered a response in the willow which stunted the outward growth of the stem. In effect, the stem dedicated all its efforts into creating a solid woody chamber around the larvae and enveloping the site with wool-covered scales.  The larva overwinters within the comfy confines of this gall and emerges in the following spring.

As far as we know, the willow is tricked into making these cones via chemical inducement – once pricked, they automatically produce this wonderful little construct for the little pricker. The willows are unable to engage in self-argument or refusal to perform.  The fly slips ‘em a mickey and wham! Bob’s your Uncle!  This scenario has been going on for eons and it is for the sole benefit of the gnat. Fortunately, although the willows are un-willowing partners in this affair, they only suffer a few embarrassing and harmless growths (harmless, that is, unless someone starts up a self argument about them.)

These galls are fascinating to look at. On the outside, they are covered with approximately 70 tough woody scales. The scales are densely covered with what botanists call “pubescence.” Internally (see below), the interior larval chamber is revealed to be a long narrow space surrounded by insulating layers of dead air space. This structure provides protection from the elements but does not shield its host from external air temperatures. Like many other fleshy little winter grubs, however, willow pine cone gnats are able to resist freezing down to -80 degrees below zero (F)!

You can clearly see a fat little yellowish thing within the central chamber of this cut-away gall (see below and here). It appears to be pupae of some sort. What I can’t tell you (“Yes you can”… “No I can’t”…) is whether that fleshy little thing is actually a pine cone gall gnat pupa.  There is a very good chance that it is not. This type of gall has been found to host an incredible number of alternate occupants – 24 species in all – including 9 harmless co-habitating species and 14 parasites. The parasites, of course, are the ones who take over the body of the gnat, kill it, and themselves overwinter in the gall.

Pine Cone Willow Galls are designed from the get-go so that the emerging gnat can simply push its way out through the overlapping upper scales like a one-way door. The adult gnat has no ability to chew its way out. Because of the vast numbers of potential predators, there is no telling what kind of creature will actually emerge from these “pine cones.” O.K., I can say with absolute surety that Martha Stewart will not – and that’s the end of it.


  1. Wow, this is fascinating! I’ve seen galls before, but the texture has always been smooth, nothing like these. I once saw a tiny “pine cone” at the Denver Bot on one of the cactuses, and even asked them about it, and no one knew what it was. I doubt cactuses get galls, but…

    Comment by Monica the Garden Faerie — March 1, 2010 @ 11:03 am

  2. I forgot to mention, Crosswinds Marsh is a great place!

    Comment by Monica the Garden Faerie — March 1, 2010 @ 11:03 am

  3. I had a somewhat similar conversation with myself the first time I saw one of these. It was stunningly beautiful (the gall, not the conversation), and I was amazed to discover what it was. Since then, I’ve really gotten “into” galls – finding such a vast assortment that it is tempting to start a gall collection.

    Comment by Ellen — March 2, 2010 @ 11:13 am

  4. “You need to shut up.” “No, you shut up.”

    Made me laugh, and taught me something, all in one post. Excellent!

    Comment by Joy K. — March 6, 2010 @ 10:53 pm

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