Summer, green as a stinkbug( 2013.4.1[Mon.])

 

  I spent a lot of time in 2012 collecting insects with my son (aged four at the time).Looking back, it seemsto methatstinkbugs were the theme that year. In July, my son captured a very large Agriosphodrus dohrni on a trip to Kyoto using his bare hands, despite my warnings about getting stung. Then that August, I collected a delightful clown stink bug Poecilocoris lewisi, and ended up turning over leaf after leaf hunting for others. Then, at a meeting in Lisbon, the only specimen I managed to obtain was, sadly, a rather common red-striped shield bug, Graphosoma rubrolineatum. The Japanese names for the clown and the red-striper differ by only by the modifier “kin” (meaning “gold”), but what a difference it is! And finally, September. Searching the mangroves of Ishigaki island, we encountered a large cluster of Calliphata nobilis that had sensed the summer drawing to a close and retreated to warmer climes.

  Stinkbugs often migrate south in swarms, and this is true even for the most common type found in Honshu, the giant jewel stink bug Eucorysses grandis. I witnessed a horde of these insects in Shioya two years ago, but for the species that I encountered in that island, I can only say you had to be there. The scale was amazing, just out of this world. There were so many stinkbugs trying to overwinter on trees it looked as if they had spontaneously self-assembled into tree-like structures. Most congregated on the undersides of leaves, but it seems those spaces had filled to overflowing leaving more to cling to the trunks of trees like sap-drinking drone beetles.

  The Japanese term for jewel bug (kinkamemushi) encompasses quite a few species, that are distinguished from other stinkbugs in that they don't give off a powerful defensive odor, although they do have some offensive chemistry (which can't easily be removed with soap and water). Given their immense numbers, their smell inevitably accumulates and can even be overpowering. I suppose the awaking lizards (Japalura polygonata) that populate the island in numbers may also find these intruders to be less than welcome guests.

  My wife tried to capture the scale of this swarm in photos, but the instant any one of them sensed even a hint of danger, the entire group would fly off. I was not able to work out just what triggered this flight behavior, which seemed like a chain reaction rippling across the entire swarm, but the end result was thousands of large stinkbugs leaping skyward together in buzzing clouds (which reminds me, the stinkbugs are relatives of the leafhoppers). It was a stinkbug storm. Actually, it might be more accurate to describe it as an artillery barrage. In these kinds of numbers, even insects can be frightening. Perhaps this is how it would feel to be at ground zero of a locust swarm. We were all a bit stunned, and even I forgot to try to net anything. And then, suddenly, the entire throng took wing and left our family alone again. The whole experience was like a dream.

  But we did manage to collect quite a few in our killing bottles and to scoop up a few stragglers by hand. Close inspection revealed that our catches showed subtle differences, some having orange ventral crests that were absent in others, with the crestless variety slightly larger in size. A bit of research revealed the thinner species to be Calliphata nobilis (called nanahoshi kinkamemushi in Japanese), while the fatter one is more properly called the red-bellied jewel stinkbug (akahara kinkamemushi); opinions differ on which species is the true C. nobilis. Whatever the case, the swarm we encountered was made up of these two species. Does that mean that together they constituted a massive colony?

    To find out, I tried trapping a whole group from a single leaf in a vinyl sack. Interestingly, all I found was C. nobilis (of the nanahoshi kinkamemushi variety). It is only a single data point, but it seems that even when they form a colony (and take flight) together, the two species remain separate when choosing leaves.

  My wife knows more about these things and tells me that birds can also form mixed-species flocks. These serve as a survival strategy in winter when camouflage is reduced after trees lose their leaves, by allowing birds to communicate with shared warning signals. This is a different mechanism than so-called mutualism; rather, it is a social or behavioral phenomenon. Species including the Japanese pygmy woodpecker (Dendrocopos kizuki), varied tit (Parus varius), Japanese tit (P. minor), Eurasian nuthatch (Sitta europaea), and longtailed tit (Aegithalos caudatus) are all known to exhibit this behavior. It was surprising to find out that insects also show this rare colony-forming adaptive strategy. The stinkbugs were clearly cooperating to signal flight... Perhaps their swarm formation evolved before, and has continued after, their speciation.

  So what became of the stinkbugs we collected on Ishigakijima? I have them all displayed in my collection, of course, nanahoshi and akahara packed side-by-side in a small case. Unfortunately, stinkbugs lose their beautiful metallic green sheen when dried. They donft look themselves at all. But even so, these deep green and lustrous stinkbugs are the most faithful witnesses of that uncanny episode on Ishigaki. Their odor still wafts out any time I open the lid of the case. But for my family, this is what we remember as the aroma of Ishigaki.

Afterword: Migrating insects now make stops on manmade islands. In October that same year, I captured an E. grandis right here on Port Island. It was no doubt heading for its winter quarters. That was my last stinkbug of 2012.