The art of teaching is the art of assisting discovery.
~Mark Van Doren
We had an adventure on one of the last weeks of summer camp at the Garden. It was all about discoveries – trees, dragonflies, aquatic macroinvertebrates, field and forest insects and animal tracks and signs. A highlight for me was sharing the incredible diversity of Mason Farm Biological Reserve with those budding naturalists. We sampled both field habitats and forest edges using various techniques from sweep nets (swinging a mesh net back and forth through tall grasses and examining your catch) to log rolling (gently turning over downed logs to check for decomposers and other critters).
The kids were excited about their finds as they swept the nets back and forth along the edge of the meadows. I was so busy helping them catch and identify things I didn’t have much time to photograph anything, but when one camper saw a tiny jumping spider in his net, I had to grab the camera. I have a weakness for jumping spiders and their bold colors, huge eyes, and “inquisitive personalities”.
I later identified it as a brilliant jumper based on the green chelicerae and the orange pattern on the abdomen. I shot several images as it crawled about the edge of the net, pausing frequently to stare up at my camera gear looming overhead. It finally did what they often do, and leapt up onto my lens, ending its photo session.
As we walked along the forest edge, someone spotted a huge wolf spider. I bent over for a closer look and a quick picture of its enormous (and numerous) eyes. I’m not sure how the common and scientific names came about (rabidus is Latin for wild, crazy, raging), but maybe some early arachnologist laid down and looked into the face of one of these huge spiders and felt a slight twinge just as I did.
We showed the campers the proper technique for rolling a log (gently roll it toward you so that any larger critters can escape away from you instead of coming at you).
One log revealed a treasure trove of beetles – some adult passalus beetles (in the family Passalidae), and several large beetle grubs. These common large beetles are also called patent leather beetles, horned beetles, horned passalus beetles, bess beetles, and many other common names,
The first two grubs were huge, curled in a C shape under the log. I did a quick glance and told the excited kids those were probably the larvae of the passalus beetles and bent down to pick one up. I then noticed another larva crawling nearby. It was slightly slimmer and was actively moving instead of being curled up.
At first, I assumed they were just different ages of passalus beetle grubs. I remembered reading that their larvae have a reduced pair of legs used for stridulation (making sound by rubbing one body part against another, in this case, the reduced leg against the adjacent larger leg).
I always had wanted a photo of the reduced pair of legs (it’s what we nature photographer types do) so I flipped over one of the larger grubs and took a couple of quick shots. Sure enough, the first pair of legs was smaller then the other two pair. We gently replaced that log to its original position and rolled another. More beetles! And something else…
There were a couple of beetle pupae under the log (I assumed they were passalus beetles). This was really cool as I had never seen large beetle pupae before. One was attached to the underside of the log in what looked like a chamber made of wood debris and maybe beetle frass.
There was also a brown-colored passalus beetle. These are juveniles and they will gradually darken to black as they mature (I wasn’t able to find how long this takes).
Passalus beetles are fascinating critters and a frequent live animal used for environmental education demonstrations. They are one of the few beetles that are social and tend their young. They feed by chewing galleries through the soft wood of downed trees and then re-ingesting their frass after it has been colonized by bacteria and fungi. They also feed this mixture to their larvae. One way they maintain this social structure is through a complex communication system created by stridulation. Adults stridulate by rubbing rows of spines on the undersides of the soft, flying wings (the membranous wings hidden under their hard outer wing structures – the elytra) against a hardened textured area on the top of their abdomen. As I mentioned earlier, the larvae can also make sounds, and these are believed to be important not only for social communication, but also defense against predators. Pick a beetle up and hold it close to your ear, and you are likely to hear some squeaks (click this link to hear passalus beetle stridulation). This same reference states that passalus beetles have 17 known audio signals for both adults and larvae, making it the most elaborate sound communication system known for any arthropod.
I was all set to write up a blog post when I double-checked my information on the life cycle using various online resources. Then it happened…I began to think I had made a mistake in my identification of the large grubs. I found a reference that stated passalus grubs have a reduced pair of legs, but it is the third pair, not the first, as I had seen on the large grubs. Plus, it said these small legs were so reduced as to be difficult to see. Dang, I had to go back and check out those grubs again. Well, as luck would have it, it rained a lot the next day and the creek rose making it tough to drive across to Mason Farm. Things were busy at work that week, but as I was walking on our nature trail one afternoon preparing for a program, I saw a log off the side of the path. I walked over and flipped it, hoping to find…
There was an adult passalus beetle and a large slender grub! There were actually a couple of grubs under that log, so I gently grabbed one and flipped it over to look at its legs.
Yes, indeed, that third pair of legs is reduced and very difficult to even see on a passalus beetle larva! So, I had been wrong in my ID on that first quick glance. Those large grubs are most likely the larvae of some other beetle, perhaps a stag beetle. Not only did they not have the greatly reduced third pair of legs, but they were all curled into a C shape. Passalus grubs are usually straighter in posture and more slender. I’m not sure about the pupae, as I didn’t manipulate them to see all sides, but I think they still may have been passalus pupae. It was a good reminder that I need to make careful observations and to double-check my information. Of course, now I want to go back and check on the pupae and see if they are still there, and, if so, maybe keep one to see what emerges. It also showed me that there is always something more to learn about even the common creatures we share our world with, and that learning truly is a life-long endeavor.