Red-shouldered Bugs

Our Springfield neighbor Cyrus asked me to identify these bugs that were covering his privacy fence.  These are nymphs of the red-shouldered bug (RSB) or jadera bug, Jadera haematoloma.  The interesting question is what are they doing here in our neighborhood?

RSB distribution - soapberrybug.org

RSB are members of the soapberry bug subfamily, Serinethinae.  There are 65 hemiptera species in the family and interest in their their evolution and adaptation to human associated changes on the planet has earned them their own webpage, Soapberry Bugs of the World.   

The sudden spread of these new species is due to adaptive radiation, "the diversification of a group of organisms into forms filling different ecological niches."  Darwin's finches evolving different beaks to adapt to varied food sources are a prime example of adaptive radiation.  For the soapberry bug family, their success is based on their evolving ability to tolerate the cyanide defenses of the soapberry plant.
 
Bugguide says RSB occur year-round in CA, TX, and FL, with peak numbers in May in central Florida but they are also found in southern Missouri and Kansas. Their native host plants are Sapindaceae family plants and the western soapberry, Sapindus drummondii, is a native species found in a few southern Missouri counties. 

Adults mating - Rebekah D. Wallace

The red-shouldered bug moniker is obvious when you see the adult.  It averages 1/2 inch long.  Most pictures of adults show them mating, either because that is what they do most of the time or that is how to find them holding still for a photograph.  They can be a nuisance like box elder bugs when they invade your home and can also stain children's clothes red when they play in an infested yard.


I think the key to why Cyrus found his fences covered with RSB nymphs lies across the street in a neighbor's goldenrain tree.  This is Koelreuteria paniculata, a native of China and Korea imported to the USA in 1763 and now a popular landscape tree worldwide.  (Editor's confession: we had one once in our back yard.)  In some areas the RSB are observed feeding so often on goldenrain tree seeds, Koelreuteria spp. (Sapindaceae), that they are referred to as goldenrain tree bugs.