GOLDENROD

This is Goldenrod (Solidago sp.) which is now just starting to come into its own.  It's all over the place in summertime but it's green like everything else so it's hardly noticed....until the flowers start to turn color.  Then you notice it.  You might also have noticed that small Flower Fly at the left.
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There's a particular Gall Fly (Eurosta solidagnis) which parasitizes this plant in the summer.  I guess, technically, it isn't a parasite as, by definition, a parasite always injures its host in some way.  This relationship where one organism (the commensal) benefits and the host organism is neither benefitted nor harmed is called Commensalism. The wasp larva is the commensal and the goldenrod plant is the host.
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This fly lays an egg in the stem of the plant which then causes stem cells to grow around the egg to ....seal it off from the rest of the plant, much like your body causes skin cells to grow around invasive viruses to form warts.  Warts are nothing but clumps of skin cells attempting to shield the body from potential harm from the invasive virus.
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It doesn't harm the plant at all but the resulting gall serves as an insulating mechanism for the developing fly maggot which over-winters in the gall which protects it from winter's cold.  In the Springtime, the fly maggot chews its way to the edge of the gall and then pupates.  When it turns into an adult gall fly it chews through the outside rind of the gall and leaves to start the cycle again.   You can read all about it here:  https://hort.extension.wisc.edu/articles/goldenrod-gall-fly-eurosta-solidagnis/    Thus endeth the biology lesson for the day.
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Wisconsin ice fishermen have known about these small maggots....roundish and a little smaller than a pea....and they pick the gall off the plants and save them in a bag in the garage where they remain cold.  Then, while ice fishing, the galls can be opened with a knife and the maggots threaded onto a fish hook and they make perfect baits for panfish (any small fish that is ready for pan frying).  I have personally used thousands of them over the years and they were responsible for many a delightful fish meal.
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BEST IN LARGE.