Snag life, part 1

It was clear
that part of my journey was happening there,
then, in that place.

Not far down the trail,
I had paused,
lifting my arms and facing the sun,
which was screaming its brilliance down
onto the naked golden woods and fields.
Screaming, in a quiet and calm sort of way.

I had taken off my eyeglasses.
With my eyeglasses off the world sometimes feels different;
this day especially.

Through these motions perhaps I had invited
the feelings that followed,
which I take to have been granted by the place.
Joy, at the discovery of a giant red oak leaf,
senesced, poised gently on the trail,
flooding my eyes in its color --
the kindest mahogany brown.
Intimidation and fear, as the sun dipped behind thick looming pines
and I strolled into their deep shadow-world.
Utter entrancement, at the sight of the bank of trees
at field's edge, backlit,
sun suffusing through in sort-of sunbeams,
steamy gray, soft, and radiant, the air still
and yet ashimmer with their energy.

On such days, sometimes, when I turn
so that the sun is at my back,
and I look up to see it booming proudly
on tree and sky above,
I am filled with the deep-colored sky,
which then I know arches far back,
to ancestor time;
I am filled with the unspeakable mystery
and energy and love of the world;
There it is, it's all there,
unfairly, intolerably.
All I can do is close my eyes,
sigh,
listen to the stirrings of my heart,
and feel filled
and yet jolted --
jolted,
in a gentle sort of way,
back to the knowledge that this indescribable thing
is here.

---

We don't always feel such things when we are out and about; it is special when we do -- special, and fleeting.  I had come to this parcel of the Upper Iowa River Wildlife Management Area hoping to do at least a little bug hunting, relationship hunting, pattern hunting, whatever you call it when you are maintaining watchfulness for patterns and recent happenings in a wild place.  So, the glasses went back on, and the entrancing vista gave way to an ever more ordinary and immediate world of tree trunks, leaf litter, bare twigs and branches, as I left the open field and walked into the adjacent woods.

Immediately my eyes locked on a particular tree.

This snag (a handy word for a dead tree) had clearly undergone some heavy excavation by large woodpeckers.

Judging by the bark, which matched that of neighbor trees that were still alive (and thus more readily identifiable), the snag was a "popple" (Populus sp.) -- apparently quaking aspen, Populus tremuloides.  Examining the bole, I noticed a curl of bark and wood that seemed especially dark underneath.

Well, doesn't look to be much of anything yet, while still in shadow like this.  Thank goodness for flash bulbs on cameras.

A bunch of exoskeletons!

Here, I've pulled up the curl to expose them.

Let's zoom in.

This is the shed skin of a firefly larva!

A larva, you ask?  Well, fireflies (family Lampyridae) are technically beetles...and, like all beetles, they pass through an immature larval stage, then a pupa stage, and then finally adulthood.  (The winged adult is our beloved flying "lightning bug.")  If you have a hard time believing that fireflies are beetles, consider this:  When you watch a firefly taking off, have you ever noticed it almost seems to have two pairs of wings?  First it lifts up one pair of thick, darkened "wings," which it holds upright in a "V."  Next it unfolds a thinner, transparent "second pair" of wings that begin to vibrate and then pull the animal aloft.  As it turns out, the first structure -- those thick, darkened "wings" held in a V -- aren't really wings at all.  They are a sort of storage cover for the real wings, the fragile, transparent membranes underneath that actually do the flying.  All beetles have such protective wing sheaths.  In fact, beetles are named for them: Coleoptera, the taxonomic order to which all beetles belong, comes from the Greek for "sheath" (koleos) and "wings" (ptera).  So if humans are the "two-leggeds," then fireflies and other beetles are the "sheath-wingeds"...the ones with the sheathed wings.

Firefly larvae, by the way, are seriously cool-looking.  They might be the spawn of an Ankylosaurus dinosaur and one of the man-eating sand worms in Tremors...only quite a bit smaller.  Here's one I came across in April 2012, prowling a sap flow on the trunk of a sugar maple:

They have this funky extensible structure on their front end:

Follow this link for another shot of a larva sticking its "neck" out.  Also on Bugguide you can see one of these larvae eating a snail (they're predatory).  And just like adults, they glow.

But getting back to the exoskeletons on the snag...evidently, in this case, a whole cohort of firefly larvae had crawled up the snag, settled under the bark curl, shed their skins to become pupae, and then (after a while) emerged as adults, sometime during a previous growing season.

OK, so a few firefly larvae might end up on a tree trunk here and there, every once in a while...but not on purpose, right?

You might be surprised!  Here's researcher Lynn Faust on a firefly species in eastern Tennessee:

"...[L]ast instar larvae of [the cold-hardy firefly species] Pyractomena borealis become active in February when snow and below-freezing temperatures are common. They gather in the furrows on the warmer, sunlit south sides of still-leafless preferred trees, the majority of which are...hickories ...and tulip poplars...." ¹

Yep, you heard right:

"[Day-active] P. borealis larvae climb from cold winter ground up preferred trees seeking sunny, protected pupation sites. Frequent moving is common in Jan-Feb as larvae select ideal arboreal sites." ²

So Lynn watched as these firefly larvae climbed tree trunks during the winter, snuggled into the warmest, coziest nooks and crannies in the bark, and then pupated there!  Which is surprising enough...but wait till you hear what she witnessed several weeks later, when the adults started to emerge (eclose) from their pupae:

Males began to eclose late in March, 9 ± 7 days...earlier than the females... There was no flashing from these first-eclosing, day-active searching males for over a week. These males, [day-active] at this stage, methodically searched the trunks for larval or pupal females by day and rested motionless in furrows at night... Every pupa, furrow or scale 3 m up the trunk was investigated. Upon locating a female, the male clasped her with his legs, pressed his pronotum to hers and became motionless. Pupae, when approached by a potential guard male, arched back and forward rapidly (12 times in 2 min in one instance) before being clasped and subdued by the male. A few male pupae (2 in 2011) were guarded, but only briefly.... All pupae guarded for over a day eclosed as females (2008-11). Competing males piled on top, grappled with, and often displaced the guard male, which would then be forced to search for another female pupa.  Males also used their pronotum to pry under or push away other males. This competition intensified as females approached eclosion, with frequent power reversals occurring among the increasing numbers of males. Female pupae 24 h from eclosing had 3-7 males competing for them... ³

Well, I suppose you can guess what the males are hoping to do once the females emerge...
and here's Lynn, confirming your suspicions:

Typically, a newly-eclosed (still white and soft) female...would be mobbed by her guard and competing males. She would rapidly leave her pupation site, seeking cover under a bark scale or crevice, with 1-3 males riding her back. Copulation commenced before her elytra had hardened and darkened and no flash dialogue was involved... ⁴

Evidently this doesn't harm the female.  Indeed, it wouldn't make sense if it did: presumably, females must remain healthy and vigorous after mating in order to successfully find an egg-laying site and deposit their eggs.  That the females emerge unscathed from these mating brawls is also suggested by both sexes' promiscuity:

Once copulation began, competing males left. If a new male arrived, brief skirmishes occurred as he tried to take the female, but did not succeed. Both males and females re-mated readily.... After copulating, the males glowed continuously. ⁵

---

Of course, all of this is not to say that it's already time to watch for the "magic lights" flashing in shadowy corners of your yard.  Those exoskeletons I found are old: the adults emerged in a previous growing season...last year, or perhaps the year before.  And we have no way of knowing if their particular tree trunk drama happened in February, April, June, or even later.   Different firefly species are active at different times of year, and there's no guarantee these belong to the same species as the ones Lynn observed.  Really, we can't say anything other than that a bunch of firefly larvae once pupated on the snag and emerged as adults.  All we have is a few wispy leftovers to hint at what might have unfolded beneath that sheltered curl of bark in a season long since past.

It's also worth mentioning that not all firefly species climb tree trunks to pupate.  In her new book Fireflies, Glow-worms, and Lightning Bugs, Lynn details some other common firefly pupation habits:

The last instar larvae seek out the perfect place to pupate according to their species needs.  For the Photinus, pink and intermittently glowing as a pupa, it is a chamber several inches underground or underneath a spongy mass of moss.  For the Photuris, glowing and cream colored, it can be an igloo-shaped cell of dirt on the soil's surface or under a log or board, often in the company of three to five other pupating Photuris. (...) It is still unclear if, in addition to the Ellychnia, other species might possibly overwinter not as larvae but as pupae or even as newly emerged yet dormant adults. ⁶

---

You might recall that its cache of firefly exoskeletons wasn't the first thing I noticed about the dead tree I came upon in the woods.  In Snag life, part 2, we'll focus on the snag's woodpecker damage -- digging in (quite literally) to the question of what those hungry birds were after.

Coming soon: Part 2

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NOTES:
1.  Page 48 in Faust, L. 2012. Fireflies in the snow: observations on two early-season arboreal fireflies Ellychnia corrusca and Pyractomena borealis.  Lampyrid 2012 (2): 48-71.
2. Ibid., p. 48.  Emphasis added.
3. Ibid., p. 60.  Emphasis added.
4. Ibid., p. 62
5. Ibid., p. 63.  Emphasis added.  The fireflies referred to in this quote were collected as pupae, enclosed in containers within their habitat, and monitored as they emerged.
6. Page 47 in Faust, L. 2017. Fireflies, glow-worms, and lightning bugs: identification and natural history of the fireflies of the eastern and central United States and Canada.  University of Georgia Press: Athens.