Eastern United States
Eudryas unio (Hübner)
Diagnosis: The basic maculation of unio is the same as in grata, but with some noteable differences. The species is smaller than grata and the forewing appears more rectangular and less ovate than that of grata. The forewing postmedial line is olive green, but is crenulated and accented with dark red-brown on its inner side. The postmedial line of grata is strongly outcurved and is even, not crenulate and not accented with dark red brown on its inner side. The reniform mark is much thinner than in grata and the oribicular mark is red brown, blending into the red brown of the costal margin. The orbicular mark is accented with olive green in grata and clearly stands out from the red brown costal margin. The red-brown patch on the inner margin is rectangular in unio, but triangular in grata. This inner patch is also flecked with blue-white scales in unio; these scales are absent or very weak in grata. The red-brown band on the outer margin of the hindwing reaches the inner margin in unio, but ends well before the inner margin in grata. The outer red-brown bands of both the ventral forewing and the ventral hindwing are distinctly present in unio, but absent in grata (although the forewing band may show through from the dorsal side.
Distribution (See Map on Left): Eudryas unio
has a wide distribution in North America. The species occurs throughout
most of the eastern United states from as far north as central New Hampshire
and southern Ontario, southward to southern Florida. The species ranges
westward to the eastern Great Plains and southward to southern Texas and
as far south as the state of Vera Cruz along the eastern coast of Mexico.
There are two apparently isolated populations of the species, one in central
Utah, and a distinctive population in California. The California population
may be referred to as subspecies brevipennis if a subspecies
concept is employed. The California population is primarily distinguished
by the presence of a discal dark discal dot on the dorsal surface of the
hindwing. A discal dot is absent on the dorsal surface in all other populations.
The California population is also slightly smaller and slightly redder
and the marginal band on the hindwing is larger and slightly better defined
than in typical unio. No significant differences in the male or female
genitalia have been found between the California population and typical
Identification Quality: Excellent
Larva: Comstock and Dammers state that the species is always found in marshy areas where both Epilobium and cattails (Typha) grow together. The larva just prior to pupation leave the foodplant and move to dry Typha stems, digging a burrow in the stem, and covering the surface with a thin silken lid. The species is two brooded in California, pupation occuring first in May and the second in December. The adult is a day flier, and are collected roughly between the hours of one to three in the afternoon. The first brood of adults in southern California occurs in March and the second in June. No similar information is available for the eastern populations of unio. The larva is nearly indistinguishable from that of grata, although mature larvae are consistently smaller. The last instar head capsule is 2.8 to 3.0 mm wide 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: Crumb (1956) listed grape (Vitis sp.) (Vitaceae), Oenothera biennis . (Onagraceae), and Ludwigia sp (Onagraceae) as foodplants. Forbes (1954) also lists lythrum (Lythrum sp., Lythraceae). Tietz (1972) lists Decodon verticillatus (Lythraceae) and Hibiscus sp. (Malvaceae) in addition to the above foodplants. The California population was described in detail by Comstock and Dammers (1938). Comstock and Dammers record Epilobium californicum (now considered a synonym of Epilobium ciliatum) and Oenothera spp., all in the Onagraceae.
Eudryas unio is sympatric with Eudryas new species 1 is southern Texas and Mexico. The species can be difficult to separate. Eudryas new species 1 is a smaller species than unio; the forewing length from the base of the wing to its apex averages 14.7 mm in unio, but only 13.3 mm in Eudryas new species 1. Some overlap in size is present between the largest specimens of Eudryas new species 1 and the smallest specimens of unio however. Two features of Eudryas new species 1 will always distinguish it from unio. First two olive-green spots are present in the forewing of Eudryas new species 1 following the reniform mark. These spots are absent in unio. Secondly, red-brown bands are present along the outer margins of both the forewing and hindwing ventrally in unio. A red-brown band is absent on the ventral hindwing of Eudryas new species 1, but is weakly, not distinctly, present, on the ventral forewing. The male genitalia of the two species are similar, but distinctly different. The saccular projection of the valve is at least five times longer than wide in unio, but only about twice as long as wide in Eudryas new species 1. The ventral-basal projection of the cucullus is well developed and hooked in unio, but triangular and much weaker in Eudryas new species 1. The ductus bursae of unio is twice as long as in Eudryas new species 1 and the ostium is deeply triangular in unio, but not in Eudryas new species 1.
The differences between unio and grata are discussed in the diagnosis section above.
Eudryas new species 0001