adulterous deer fly

Adulterous deer fly is a common, relatively small, deer fly. It occurs in the United States and southern Canada east of the Great Plains.

Adulterous deer fly larvae are aquatic and predaceous, feeding on other insect larvae and on worms. Adults are active from June through August in Minnesota. They are found in open woodlands and wetlands, often near the margins of streams and ponds.Males feed on plant nectar. Females feed on the blood of mammals.

Males are 5⁄16″ to ⅜″ (8.2 to 9 mm) in length. They are relatively rare, and they are difficult to identify to the species level. Female adults are ¼″ to 5⁄16″ (7.1 to 8.4 mm) in length. The body is stout and brownish yellow with dark markings. The wings have dark markings.

The head is broad, and it is covered with light yellow hairs. The compound eyes are bulging, iridescent, and brightly colored. On males they meet at the top of the head. On females they do not meet. There are three simple eyes (ocelli). The area around the ocelli (ocellus spot) is brown with three black spots and an ocellus in the center of each spot. Females have a large, bare, hardened area (frontal callus) on the front of the head between the compound eyes. The frontal callus is entirely brownish black and not very shiny. The antennae have three segments. The first segment (scape) and second segment (pedicel) are reddish yellow and are densely covered with fine black hairs. The third segment (flagellum) is long, clearly ringed, and black. The large, bare, hardened area on the face (facial callus) is reddish yellow. The small, bare, hardened areas on each cheek (cheek callus) is brownish black or black. The mouthparts are modified for piercing flesh. The finger-like sensory mouthparts (palps) are reddish yellow.

The upper side of the thorax is bluish green with a narrow brown longitudinal stripe in the middle and a broader stripe on each side. On each side of the thorax there is a brown stripe between the base of the wing and the shoulder (humeral) angle.

The abdomen is brownish yellow with 4 blackish-brown longitudinal stripes, 2 in the middle (middorsal stripes) and 1 on each side (lateral stripes). It has 7 segments (tergites). The first segment (T1) has a brown spot in the middle. On T2 the middorsal stripes merge in the front either broadly or narrowly, creating an inverted V, or they are very narrowly separated in the front. The lateral stripes are either poorly defined or they are missing altogether. T4 through T7 become increasingly blackish.

The wings are clear with dark markings, including a dark leading edge (costa), a broad dark band in the middle (crossband) and a dark spot at the tip (apical band). The area between the crossband and the apical spot (hyaline triangle) is clear. Details of the extent and shape of these markings are important identifying features of species in the genus Chrysops. The dark markings are not broken by pale areas bordering the veins. The hyaline triangle is very small and truly triangular. It is restricted to the ends of cells m1 and m2.

Female total length: ¼″ to 5⁄16″ (7.1 to 8.4 mm)

Male total length: 5⁄16″ to ⅜″ (8.2 to 9 mm)

Open woodlands, wetlands, the margins of streams and ponds

June through August

Larvae are aquatic.

Other insect larvae and on worms

Males feed on plant nectar. Females feed on the blood on mammals.

Sources

29, 30, 82, 83.

Infraorder
Orthorrhapha was historically one of two infraorders of Brachycera, a suborder of Diptera. However, Orthorrhapha was paraphyletic, meaning that it did not contain all of the descendants of the last common ancestor. It was split into five extant (still existing) and one extinct infraorder. Orthorrhapha is now considered obsolete and has not been used in the last decade, but it persists in printed literature and on some online sources. A recent revision of the order Diptera (Pape, et al., 2011) revived the name Orthorrhapha, but this has not been widely accepted.

Alfredo Colon
6/17/2024

Location: Albany, NY