Naturespeak A naturalist's view of the world

December 14, 2007

Deck the Halls with Galls

Filed under: Uncategorized — wykes @ 8:50 pm

  Once again I find myself returning to the subject of galls, but I do so without apology.  I may be showing a lot of gall in doing so, but not really.  There are literally thousands of gall types and I could theoretically focus on a different gall for each of the next thousand columns. I could change the name of my site to Gallspeak and even highlight a “Gall of the Month” -or not. To do so would reduce my readership by half and leave me with only one person (who happens to have the same last name as I do) out there to read this stuff.  Besides, how many times can a sensible human being stand titles like “It takes a lot of Gall,” “A Galling Truth,” or even “Deck the Halls with Galls” before going numb.

  So, I present to you two familiar plant galls that you can literally go out and see on your next outside walk.  The first is called the Goldenrod Ball Gall and the second is the Goldenrod Bunch Gall.  Both of these galls are found on, you guessed it, the dry winter stems of Goldenrod flowers. If your walk takes you by an un-mowed field there’s a good chance you’ll find one or both of these galls.  You might even want to take at least one of these galls home for further investigation or appreciation.

  Before we take a closer look, let me remind you that galls are swellings or particular growth patterns caused by an insect egg. As soon as the insect lays her egg in the stem, the plant reacts to the violation of inner tissue space by forming a special scar tissue.  It is believed by some that a chemical introduced by the mother insect actually imitates the growth hormones of the plant and causes it to grow in a very specific way. The egg hatches into a larvae and the larvae completes its growth inside the plant swelling.

  In the case of the Goldenrod, the two galls in question are both caused by two unrelated flies (see the one responsible for the ball gall here). Both have impossible scientific names ending in solidaginis. This should give you a good indication that these gall creating insects are very loyal to their plants.  The scientific name of goldenrod plant is Solidago (which means to “make solid” as in healing properties) and those insects who associate with them are given the same general name. It’s something like someone named “Bud” who drinks a lot of Budweiser.  That’s not a great analogy, but I hope you get my point.

  The Goldenrod Ball Gall is a round hard woody structure which gives the bare stem the look of a rigid upright worm that swallowed a golf ball.   I passed this particular structure many times over the past few months – taking a picture of it in October and finally taking it in last week for a closer look. I wanted to cut it open to reveal the snug fly grub that spends the winter within.  Ice fishermen have long known that ball galls host a fat white ¼ inch larvae perfect for attracting their quarry to the hook.  Since these tender little balls of insect pultritude are vulnerable to freezing, they build up high levels of glycol antifreeze in their blood.  When you take them out on a cold day they appear to be frozen solid until warming up in your palm.  

  This particular gall specimen proved to be empty. It is likely that the grub was attacked by a fungal growth and reduced to dust.  You will also find that these galls are often pecked open by Downy Woodpeckers and Black-capped Chickadees who appreciate their succulent contents.  If left to their own, the grubs will emerge next spring. The adult fly will exit via a tunnel chewed by the grub before it pupated and punch its way through the thin outer layer.

  A completely different kind of structure is expressed by the Goldenrod Bunch Gall.  This flower-like leafy growth is only found on Canada Goldenrods.  Its creator is another fly called a Gall Midge which looks like a beakless mosquito.  This midge lays multiple eggs that eventually hatch and enter multiple chambers created by the cluster growth. The goldenrod plant essentially ceases to grow any more stem but continues to produce an explosion of leaves. 

  Because the adults emerge out of these leafy galls in September, the gall insects are gone by the time you find them in winter.  It is therefore relatively safe to bring bunch galls inside for ornament treatment. A nice spray of gold paint will turn them into magical natural decorations. Before beginning your artistic endeavor, however, give the thing several taps in order to remove the other critters that use them as winter homes.  Yes, investigators have discovered that 30 some species of arthropods – from spiders, to mites, to other insects – use the protective cover provided by bunch galls to their advantage. To have this mini-menagerie emerge from their golden castle within the confines of your home would be, well, galling.

1 Comment »

  1. Galling… but interesting! I should find out if the fishermen around Maston Lake here in Michigan really take advantage of the larvae for ice-fishing. Mmmmm… maybe a new project?

    The Gall with the Same Last Name

    Comment by Kathy — December 30, 2007 @ 5:13 pm

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