Crawlies with Cri: Shield-backed bug (Stethaulax marmorata)

Shield-backed bug (Stethaulax marmorata)

This week’s crawly has a familiar shape and is part of a familiar family but is quite unique. Meet the Stethaulax marmorata – shield-backed bug. We’ll call them “marmor” for short.
Don’t panic. These are not marmorated stink bugs. “Marmorated” means “To be veined or streaked like marble”, so it’s used as a descriptive name of more than one species of critter. Marmors absolutely look like they are carved from bits of beautiful marble.
Marmors aren’t considered pests; they will munch on a few berries or seeds of trees in the cypress family, and that’s it. There are few reports of marmors in our area, so getting to see one of the marbled beauties is a treat.
Marmors are true bugs in the Superfamily Pentatomoidea which has six families and around 350 species. The superfamily includes, in part: stink bugs, shield-backed bugs, burrowing bugs and dark bugs.
All the bugs in the superfamily have that sink bug-like shape – “shield-shaped” if you will. Most do have an odiferous defense like stink bugs which gave stink bugs their unfortunate moniker.
For all the similarities among the various families and species, shield-back bugs like our marmor still manage to stand out.
True bugs in marmors’ superfamily can fly. Like beetles they have thick wing covers covering most of their membranous wings for protection – one over each wing – which open to the side when flying.
Not marmors though. The plate at the top of their abdomen, just below their head – called the scutellum – is size XXL and extends over their entire abdomen (in most bugs it’s a tiny triangle). This gives shield-backed extra protection for their wings and bodies but makes flying unique for them.
They have to raise up that scutellum like a garage door before taking flight. They’re surprisingly good flyers despite the wind resistance caused by having a solid shield in front of their wings in flight.
Shield-backed bugs are also more rounded in shape than their stink bug cousins and more domed in profile. At just over one-quarter of an inch in size and with their nifty camo, they can be tricky to spot, but fun to observe.
Shield-backed bugs are also called “jeweled bugs” because several species – not found in our area unfortunately – are quite jewel-like. They don’t sport marmors’ camo coloring, but are boldly colored, shiny and often metallic.
Marmors have “piercing sucking” mouthparts like other true bugs. So, they are really drinking berries and seeds, not chewing them. They get to go through life taking their own built-in straw wherever they go. They’re always ready to belly up to the berry juice bar.
While marmors can get nutrients from drier seeds, they prefer younger seeds that have more juices. Who can blame them? We’ve all tried to drink that too-thick milkshake through a straw and it’s just no fun at all.
There are few sightings of marmors in our area, but if you have trees in the cypress family keep your eyes peeled for these little marbled beauties.