Butternut woollyworm

Butternut woollyworm is a common sawfly. It occurs in the United States east of the Great Plains and in southern Ontario and Quebec. It is most common in the northeast, rare in Minnesota. The larva is host-specific, feeding almost exclusively on the leaves of butternut and black walnut, though it has been collected on hickory in the northeast. Adults feed on pollen, nectar, honeydew, sap, and other insects.

Females are 5 ⁄16″ (7.7 to 8.4 mm) long. Males are smaller, ¼″ (6.3 to 6.8 mm) long.

The head is mostly black. The sensory organs on the upper jaw (labial palpi) and lower jaw (maxillary palpi) are brownish. The antennae are thread-like, stout, and mostly black. They have 9 segments. Segment 2 is longer than wide. Segment 3 is longer than segment 2. Segments 5 through 9 are reduced in size and are brownish on the underside. Segments 7 and 8 are not broadened at the tip.

The body is robust and entirely black. The thorax and abdomen are broadly connected. The middle thoracic exoskeletal plate (mesoscutellum) is covered with deep, closely spaced punctures. The female has a saw-like ovipositor at the tip of the abdomen.

The wings are mostly clear and evenly tinged brown. On the forewing, the anal crossvein is oblique. On the hindwing both the radial sector (R_s) cell and the media (M) cell are present. On the male the hindwing does not have a peripheral vein.

The legs are long and slender and mostly white. The basal half of the first segment (coxa) of each leg is black. The second segment (trochanter) has two segments. On the hind leg the end third of the third segment (femur), the end third of the fourth segment (tibia), and the tip of the last section (tarsus), are black. On the front leg the tibia has two spurs at the tip.

Late stage larvae are ⅝″ to 13⁄16″ (15 to 21 mm) long. The head capsule is white with two black eye spots. The body is densely covered with white, cottony or woolly, hair-like processes (flocculence). This feature gives the species its common name. The flocculence is shed with each molt. Late stage bare larvae are pale green.

Male: ¼″ (6.3 to 6.8 mm)

Female: 5⁄16″ (7.7 to 8.4 mm)

One generation per year in Minnesota: July and August

Leaves of mostly black walnut and butternut, but it has also been reported on hickory.

Pollen, nectar, honeydew, sap, and other insects.