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The adults are large, 9-12 mm in length. Teskey (1990) describes the females as having a nearly square clypeus with a median pruinose (powdery) band extending half its length; extensive glossy areas on the head; brown palpi; and slender antennae with yellow at the base and darker apically. The thorax is black with yellow hairs, and faint stripes on the scutum; the legs are black, sometimes with reddish tints; and the apex of the wings is entirely clear. The first two segments of the abdomen are orangish, while the remaining are a lighter yellow color on the margins with progressively larger black median spots on the posterior tergites; the median spot on tergite 2 forms a pale median triangle (Teskey 1990). The males are similar, except the thorax and abdomen are almost completely black, and abdominal tergites 1-2 only occasionally having small yellow lateral patches (Teskey 1990). Chrysops excitans is readily identifiable by the combination of the pruinose stripe on the clypeus the entirely clear apex of the wings. It can only be confused with C. dawsoni, which was considered variant of C. excitans until Philip (1959), but C. dawsoni lacks the pale median triangle of tergite 2 (Teskey 1990). The larvae are light green, 18-20 mm long, with a stigmatal spine. They can be distinguished from other Chrysops larvae by the reduction in the pseudopodial pubescence on segments 5-10; the pubescence does not span the gap between pseudopodia. (Teskey 1969).

Little is known specifically about the life history of C. excitans. Adults are known to be more active in the morning than the afternoon, and to prefer open habitat to the edge of woodlands (Ossowski and Hunter, 2000). The eggs of C. excitans are laid in triple-layered egg masses averaging 9.8 mm in length, 3.8 mm in length, and 2.2 mm in height; the eggs themselves are brown, average 1.6 mm in length, and consist of about 450 per egg mass (Iranpour et al. 2004).

Nothing is known of the dietary habits of the larvae of C. excitans. The adults subsist mainly on flower nectar, but aphid honeydew comprises a sizable part of the diet, as over half the deerflies at Algonquin Provincial Park in Ontario were shown to have consumed honeydew (Ossowski and Hunter, 2000).