About Syrphus knabi Shannon, 1916
For terminology, refer to the Speight key to genera and glossary. This species measures 7.2–12.9 mm (0.28–0.51 in) in length. In the head, males have bare holoptic eyes, meaning the eyes are completely joined. The male frons is yellow, yellow pollinose on the upper two-thirds, and marked with a pair of brown anterior spots on the lower one-third. It shows a bluish green reflection, has a black spot above each antenna, and bears fine, rather long black hairs that extend a short distance down between the antennae and eyes. In females, the frons is black and sparsely pruinose on the upper one-quarter, and is otherwise mostly yellow, densely yellow pruinose, and commonly slightly darkened medially. The anterior part of the female frons is narrowly shining yellow and also bears a pair of brown anterior spots. At the vertex, the frons is roughly as wide as the length of the third antennal joint, and widens quickly moving down toward the antennae. On the thorax, the scutum is broadly and distinctly yellow pollinose along its lateral edges; the ground color of the thorax sides is bright yellow and covered with yellow pile. The scutum has two clear median stripes, bright yellow sides, and light golden pile. The scutellum is yellow with a greenish sheen, covered with black pile except on the sides, which have yellow pile. The pleurae are a slightly paler yellow than the lateral stripes of the dorsum, and bear golden pile. The abdomen is black with yellow bands. The band on the second abdominal segment is broken in the center, extends forward, and reaches onto the sides of the first segment. The bands on the third and fourth abdominal segments are continuous and straight, and extend over the abdominal margin across nearly the full width of the bands. The wing membrane is extensively covered with microtrichia, with cells br and bm almost entirely bare. The squamae bear rather long, light yellow pile. For the legs, the front and middle femora are yellow and covered with yellow hairs, while the hind femur is yellow with the apical half mostly brownish, and has few to many black hairs on its anterior side. The middle basitarsi have yellow spicules on their underside, and the first tarsomere of the middle leg only has yellow setulae on its underside. The first tarsomere of the hind leg is mostly or entirely orange on its upper side. The front coxae and trochanters are dark gray, and the hind trochanters are yellowish. The front and middle legs are entirely yellow, while the hind legs are yellow with a dark band beyond the middle and yellow on the posterior side. The hind tibiae are darkened on the outer side of the apical half and covered with black pile. The last four tarsal joints of the hind legs are also darkened.
