Oak Apples & Plums

In the final hours before our deadline, as we finished up the introduction to Tracks & Sign of Insects, Noah threw in this sentence: “We no doubt missed many things and probably misidentified a few.”  I knew the first part was true, but hoped he was wrong about the second part.  Alas, as I have continued to delve deeper into the world of invertebrate tracking, I have indeed discovered that a few of the photos in our book are misidentified (although, to be fair, there is no “we” about it; I can take full credit for all of the mistakes discovered so far).

Fortunately, Stackpole has corrected all the errors I told them about for the second printing, which is now available.  These are not all misidentifications; there were also some incorrectly cropped photographs and a number of mistakes in the index (which, thankfully, it was not our job to put together).  The new books do not say “second printing” anywhere that I can see, but they are easily recognized because on the cover our names have been shifted to the left to make way for two gold medallions (as shown in the right sidebar). Stackpole has not yet sold all of the first printing copies, so the only way to be sure you’re getting the newer one if you order online is to get it at NorthernNaturalists.com.  It’s not different enough to warrant buying it if you already have the book, but I’m mentioning this for those who don’t have a copy yet.

Anyway, one of my bigger goofs involves the “oak apple” galls on page 390.  It turns out there are several more kinds in New England than I thought when I put that chapter together.  Two types are illustrated, in each case with one of the galls cut open to show the interior, and both are mislabeled.  They are the same two types that I’ve placed side by side in the photo below.

The one on the left is labeled in the first printing as Amphibolips confluenta, the “spongy oak apple.”  It is solid on the inside, and when fresh has a moist, applelike consistency; I incorrectly assumed that this becomes spongy when dry.  The reason I had not found this gall’s correct identification among the “oak apples” in the gall references I had checked is that it isn’t an oak apple. Oak apples form on oak leaves, or in some cases consume the entire leaf, emerging directly from the leaf bud.  Ironically, these galls that are more applelike inside than any of the true oak apples are called plum galls (Amphibolips quercusjuglans), and they form on the sides of acorn caps.  I have yet to find one still attached, but there is an example here.  I’ve collected a number of fallen oak plums, but so far all that have emerged are moth caterpillars.  I may have to wait a while to see the wasps.  MJ Hatfield collected a bunch of galls on September 2, 2008, and had the first adult emerge on April 3, 2011 (see here)–after three winters!

True “spongy oak apples” are more like this (the one on the left is torn open to show the spongy interior)…

…except I’m not sure if these are A. confluenta or A. quercusspongifica.  The two are described in the literature as being similar in size and appearance, but apparently there is a difference in phenology.  Weld (in Cynipid Galls of the Eastern United States, privately published in 1959) wrote that adults of A. quercusspongifica have all emerged from their galls by the end of June [in Chicago, DC, Connecticut, and Ontario], whereas galls of A. confluenta in Ithaca, NY still contained pupae on August 1 and adults on September 12, and in Connecticut and Toronto adults were recorded as emerging from galls in November. The photo above was taken in May, as was the one below, which (showing a shinier and bumpier gall) seems to represent a different species:

I’m hoping to get adults from the various spongy oak apples this year and get them sorted once and for all.  Now, back to the first photo in this post.  In the first printing, the type of gall shown on the right was labeled as Amphibolips quercusinanis, the “larger empty oak apple.”  The gall made by that species is in fact very similar to this one: spotted on the outside; largely hollow inside, with the central cell (in which the wasp larva develops) suspended by radiating fibers.  I probably could have gotten away with keeping that label without anyone calling me on it.  But the spotted, “empty” oak apples that are found in late August, as the ones shown in the book were, are caused by Amphibolips cookii. The true A. quercusinanis adults have already emerged by the end of June.  A. quercusinanis galls are the ones that dry and become like brown ping-pong balls littering the forest floor; A. cookii galls wrinkle when they dry, and they average substantially smaller (the ones shown in the book are exceptionally large at about an inch across).  There are still other Amphibolips oak apples in New England, not all of which are caused by species that have been given names.  A. quercusinanis galls are so common that I have apparently never bothered to take a picture of one, but I did get an adult from one last year:

At 5 mm long, this is the largest gall wasp I’ve seen.

Someday, when I’ve got a better handle on them, I’d like to make an updated, more user-friendly and better illustrated version of Weld’s book on cynipid galls of eastern North America.  Since the wasps can take several years to develop, and since most of the galls I collect produce parasitoids or inquilines, progress is slow, and I doubt that’s going to be anytime soon.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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8 Responses to Oak Apples & Plums

  1. Ika says:

    “I’ve collected a number of fallen oak plums, but so far all that have emerged are moth caterpillars.” — Now isn’t that just a tad intriguing? Who are they? What are they doing there? Specialized inquilines?

    • I’m hoping to find out… one or two spun cocoons under the galls in the rearing container, but conditions have not been ideal for their survival–at first moldy, and then very dry. I also collected several cynipid fuzzy oak leaf galls last fall, from which moth frass issued for a few weeks. Those caterpillars remaining in the galls may stand a better chance of becoming adult moths.

      I’ve been doing a lot of research on microleps lately, and I’ve come across several references to moths being reared from galls. Most of them have been gelechiids. I have not pursued those references to find out if the species are only known from galls. Last spring I broke open an aphid gall on witch hazel and found a moth larva inside; there was no visible entry hole, which makes it seem like an egg was intentionally deposited when the gall was first developing. Coleotechnites colubrinae is believed to feed on the psyllids in the galls it inhabits, so maybe that’s what was going on in the aphid gall too. I had this Coleotechnites seemingly emerge from a cynipid fuzzy oak leaf gall, but it may have just been very small and inconspicuous when I collected the leaves. It ended up feeding extensively on the leaf surface and then pupating among the fuzz of the gall.

  2. David McIntyre says:

    My first printing of Tracks & Sign has, on the copyright page (about halfway down), a countdown from 10 to 1: “10 9 8 7 6 5 4 3 2 1″ (right above where it says “First edition”). On the second printing, the countdown should end at 2. Each subsequent printing will remove the subsequent digit. This is a common publishing convention to indicate the number of the printing. I can only guess at the origin: Once upon a time, I assume, this was the easiest way to make a change to a page in a book. My understanding is that these days it’s not much more trouble to change everything on a page than it is to change a single digit, but the convention lives on. And if you go through more than 10 printings, well, it’s time for the revised and expanded second edition!

    • Ah, thanks for the tip. I sure hope I don’t have to go through ten printings to convince Stackpole to do a second edition! I’ve got so many things I’d like to add, including your millipede eggs. When I asked my editor about it a while back, he said they’d want to wait at least five years, and then assess whether it would be a good idea. In the meantime, I’ve got another project brewing… which I’ll announce as soon as I have a publisher for it.

  3. Bug Girl says:

    I hope you will write that book! I would totally buy it! :)

  4. Pingback: Big, Beautiful Parasitoids | BugTracks

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