Eudryas grata (Fabricius)

Bombyx grata Fabricius, 1794, Entomologiae Systematica, 3(1):457.

Phalaena Pyralis cludialis Martyn, 1797, Psyche, pl. 13, fig. 31.

Eudryas assimilis Boisduval, 1874, Revue Mag. Zool., series 3, 2:59.

Diagnosis: Eudryas grata is the largest of the three species of Eudryas. The forewing length from the base of the wing to its apex averages about 20 mm in grata, 15 mm in unio, and only 13 mm in Eudryas new species 1. The forewing is slightly elongate and has a distinctly ovate appearance that is difficult to describe in words but readily apparent in the color photo of the adult. The middle of the forewing is pure white, the white stretching from the base of the wing, through the middle of the median area and wrapping up around the outside the reniform mark to the costa. A band of deep red-brown occupies the forewing costa from the wing base to above the reniform mark. The inner margin contains a conic dull dark gray patch accented out its outside by a dull olive-green band. The antemedial line is present only on the costal margin and is a dull olive-green band. The orbicular mark is olive green, round, with a central white dot and a white line defining it on the outside. The orbicular mark is well defined within the dark red-brown costal band, but diffuses into the white central area. The reniform mark is kidney shaped with a slightly lighter central line. The upper half is more distinct than the lower half. The postmedial line is a wide, olive-green band, sweeping in a wide arc around the reniform mark and steeply inward to just before the inner margin. This line is smooth, and not scalloped. The region between the postmedial line and the outer margin is almost uniformly dark red-brown except for two fine, light gray, irregular lines near the outer margin. The ventral forewing is primarily yellow orange. The orbicular and reniform marks are well defined by dull black. The dark red brown of the dorsal forewing shows through, but is not distinctive. The hindwing is yellow orange. The discal dot is absent dorsally, but shows through from the ventral surface of the wing. A dark red-brown band is present along the outer margin, but ends well before the costal margin. The ventral hindwing is yellow orange with a small, but distinct black discal dot. The male genitalia are distinctive and nearly twice as large as in either unio or Eudryas new species 1, and the tip of the male abdomen is swollen and the genitalia covered with long scales. The saccular projection of the valve has a dorsal basal knob and a dorsal, more distal prong. The juxta is extremely narrow and elongate. The female genitalia are equally distinctive with a deep, concave trough in the ventral part of the eighth abdominal segment caudal to the ostium. A central secondary depression is present at the bottom of this deep trough. The ductus bursae lacks the internal spiculation found in both unio and minigrata.

Distribution (See Map on Left): Eudryas grata has a wide distribution in the eastern half of the United States. The species appears to be absent from Maine, New Hampshire, and Vermont, occuring from central New York, Massachusetts and southward to the tip of southern Florida. Westward the species enters Canada in southern Ontario, but otherwise is unknown from the country. The most northern records and the northwestern limit of the species are in eastern North Dakota and western Minnesota. The species occurs throughout the southeastern United States, westward to eastern Texas and northward through the eastern Great Plains to North Dakota. The species is not variable, although males are slightly larger than females.

Adults are nocturnal and fly primarily in June, July, and early August throughout most of its range. The flight period is considerably longer and irregular in Florida and eastern Texas.

Identification Quality: Excellent

Larva: The larva is blue white with a tranverse medial orange stripe on each abdominal segment and the mesothorax and metathorax. The orange stripe encloses the spiracle, although the spiracle is located on the cephalad side of the band. The orange stripe runs around each segment from proleg to proleg or to the level of the proleg for those segments not having prolegs. The orange stripe is accented on either side by a dark brown line. Two dark brown transverse lines are found to either side of the orange stripe ending at approximately the same level as the orange band, although they may be weakly continued on ventrally on abdominal segments one and two. The setal insertions are surrounded by dark pinacula, although the pinacula may be fused with one or more of the dark brown lines. The dark pinacula are particularly conspicuous on the dorsal parts of abdominal segment eight and the thoracic segments. The head is orange with dark brown pinacula about the setal insertions. Riley (1870) describes the larva as feeding on the leaves of the foodplant, eating all of the leaf. The larva pupates in a cell dug in soft bark or the pith of stems (Forbes, 1954, and material in the USNM) making flimsy cocoon partially constructed of pieces of the bark or pith. The pupa overwinters and the adult emerges in the early summer of the following year. The larva is nearly indistinguishable from that of unio, although mature larvae are consistently larger. The last instar head capsule is 2.8 to 3.0 mm wide in unio versus 3.2 to 3.4 mm in grata. The second segment of the larval antenna is dark brown in unio, but is lighter in grata. The head setal character listed by Crumb (1956) does not appear to be consistent between species.

Foodplants: The larva has been described by Crumb (1956) who reports grape (Vitis sp.) as the foodplant. Forbes (1954) reports both grape and ampelopsis (Ampelopsis sp.) as foodplants, both in the Vitaceae. Other foodplants have been recorded, but these records are probably accidental occurences or errors.

Similar Species

Eudryas unio

Eudryas new species 0001