More Firewood Dwellers

I’ve been splitting a lot of firewood lately, and every once in a while I hit a log just right to reveal something interesting inside.  Everything shown below came from red maple, just as the beetles and wasps shown here did.

Tracks & Sign of Insects illustrates some frass rods of ambrosia beetles (Curculionidae: Scolytinae) that were inside some of Noah’s firewood.  The structure and characteristics of the galleries are described (p. 433-4), but we didn’t include any photos showing cross sections, I guess because we hadn’t found any worth photographing at that point.  Well, the other day I hit the jackpot:

Just as described, these galleries excavated by the adult beetles run perpendicularly to the grain of the wood, rather than just under the bark as in the commonly seen galleries of the closely related scolytine bark beetles.  Each short branch in the gallery was a cell where a larva developed, eating bits of fungus harvested from the main tunnel and fed to it by its parents.  A couple of these cells had pieces of adult beetles in them:

I think these photos might be sufficient to identify the beetles if the right person saw them, but I’m not sure who that would be.

Just under the bark of some of the same logs, I found some oval “nests” made of bark fragments.

These are surely pupal cells made by beetle larvae, but I’m not sure who exactly.  The well-known pupal cells like this are made under pine bark by the ribbed pine borer, a long-horned beetle (Cerambycidae: Rhagium inquisitor).  I have no idea what species would do this under red maple bark, but presumably it’s some other long-horned beetle.

You might notice that there are some larval remains inside a few of those cells.  Here’s a live example of the same thing:

You need to see a side view to appreciate how well adapted these are to living under bark:

This is the larva of Cucujus clavipes (Cucujidae), the red flat bark beetle.  I photographed an adult ten years ago and apparently haven’t seen one since:

Virtually nothing is known about these common beetles, but they are presumed to be predatory on other arthropods.  I’m pretty sure they are unrelated to those pupal cells.

Another swipe at a red maple log narrowly missed this wood-boring larva:

At first I wasn’t quite sure what I was looking at, but I nudged it forward to get a better look, revealing the telltale terminal appendage.

This is the larva of a horntail (Siricidae), one of the primitive hymenopterans that were formerly known as the “Symphyta”–the other included groups being sawflies and wood wasps.  I’m not sure what that appendage is for, other than to tell me that it’s a horntail larva.

The galleries of horntail larvae are densely packed with fine frass, in contrast to the coarse, shredded splinters made by many long-horned beetle larvae.

All but one North American horntail species feed on conifers, so given that this one was in a red maple, it’s safe to say it would have grown up to be one of these:

A female pigeon horntail (Siricidae: Tremex columba) ovipositing in a tree.

At just 8 mm long, this larva was far from full-grown, and although it was missed by the maul, it was doomed by having its tunnel split in two.  So I fed it to the chickadees and threw the log in the fire.