Order Hemiptera (True bugs) 
The most distinguishing characteristic of the order is the mouthparts that are modified into an elongated, sucking beak.  Most adults have hemelytra, which are modified leathery forewings.  Some adults and all larvae lack wings; both most mature larvae posses wing pads.  Both adults and larvae have three-pairs of segmented legs with two tarsal claws at the end of each leg. Many families are able to also utilize atmospheric oxygen.  This order is generally not used for the biological assessment of flowing waters, due to their ability to use atmospheric oxygen.  Several families are described. 



Corixidae (Water boatman): Broad triangular beak; forelegs are scoop-like and fringed with hairs; antennae are short and concealed beneath the eyes. Swimmer; Predator; VS-M (H)(S)


Gerridae (Water striders): Variable body shape; cylindrical beak; rear legs extend well beyond the tip of the abdomen. Swimmer; Predator; VS-M (H)(S)


Mesoveliidae (Water treader): Antennae longer than the head; long slender spiny legs with three segments. Swimmer/crawler; Predator; S-M (U)(S)


Notonectidae (Backswimmer): Body cylindrical; antennae are short and concealed beneath the eyes; hind legs are oar-like; hind tarsal claws inconspicuous. Swimmer; Predator; M (H)(S)



Belostomatidae (Giant water bug): Large oval body; antennae are short and concealed beneath the eyes; raptorial front legs. Swimmer/clinger; Predator; M-VL (H)(S)


Hydrometridae (Water measurer): Body slender and elongated; antennae longer than the head; head usually longer than the thorax; legs are long and slender, each with two claws. Clinger/crawler; Predator; S-M (H)(S)


Nepidae (Water scorpion): Body long and cylindrical; antennae are inconspicuous and concealed beneath the eyes; forelegs are raptorial other legs are long and slender; abdomen terminates into a long breathing appendage. Clinger/crawler; Predator; M-L (H)(S)