This lemon balm clump has just plain exploded, with warm weather and plenty of water helping it along.
During the winter it was pruned down nearly to the ground – an action I took only because the owner of the property might object to lots of dead, standing stems. Dead stems are sometimes problematic – some eco-gardeners (including me!) would like to leave them in place to decay naturally and provide lots of interesting micro-habitats. But when you don’t actually own the land, you sometimes have to compromise.
Among the leaves was this visitor, a greyish shield bug in the family Acanthosomatidae of the order Hemiptera (true bugs).
My best guess is that it’s in the genus Elasmucha, but there are several other related genera to which it might belong. UPDATE: It is almost certainly Euschistus conspersus, the conspersus stink bug, closely related to Elasmucha.
Like all true bugs, shield bugs have sucking mouth parts that resemble a syringe. Some true bugs use their mouth parts to attack other insects and drain them of their internal juicy goodness, leaving behind an empty shell that might be mistaken for a cast-off exoskeleton. Others, like this shield bug, use them to suck the juices out of plants.
Their forewings are divided into a hard, leathery front part and a filmy, veined rear part, placing them in the suborder Heteroptera. The other suborder, Homoptera, contains creatures like aphids, cicadas, and planthoppers.
You can read more about the Acanthosomatidae in the Wikipedia article.