Asterocampa clyton

Description

The Tawny Emperor (Asterocampa clyton) is a medium-sized brush-footed butterfly (Nymphalidae) closely related to the Hackberry Emperor (A. celtis) and sharing its exclusive dependence on hackberry trees. The wingspan is 5-6.6 cm. The upperside is mostly dark brown, with the forewing a warmer orange-brown bearing pale orange-yellow spots. The key field mark distinguishing it from the Hackberry Emperor is the absence of white spots near the forewing tip — the Tawny Emperor's spots are all orange-yellow, while the Hackberry Emperor has at least one conspicuous white spot in the subapical field. The underside is greyish-brown with subtle darker markings. A dark morph occurs regionally, with nearly uniformly dark hindwings.

The species ranges across eastern and central North America from southern Canada to northern Mexico. Like its congener the Hackberry Emperor, it is an ecological "cheater" — adults rarely visit flowers, instead obtaining nutrients from tree sap, rotting fruit, carrion, and dung. This unusual feeding strategy means the species provides no significant pollination services, functioning more as a parasite of its host trees than a mutualist.

Lifecycle

Two broods are produced per year. Females lay clusters of green eggs on hackberry leaves. The larvae are green with yellow, white, or greenish longitudinal stripes. Like the Hackberry Emperor, half-grown larvae from the second brood hibernate through the winter in the fallen leaf litter beneath the host tree and climb back up the trunk in spring to resume feeding. Pupation occurs on the host plant. Adults emerge in early summer and late summer and are on the wing from May through September.

Ecology

The Tawny Emperor is entirely dependent on hackberry trees for reproduction — no other host plants are used. In Ontario, the rare Dwarf Hackberry (Celtis tenuifolia) is the primary native host, making the butterfly's presence conditional on the conservation of this critically imperiled tree and its dry savanna and barren habitats.

Adults feed on tree sap, rotting fruit, carrion, and dung — the same non-floral resources used by the Hackberry Emperor. Like its congener, it is an ineffective pollinator, classified as a "cheater" in plant-insect mutualism research. The species is frequently seen near water, along gravel driveways, in gardens, and in woodlands — habitats where hackberry trees are present and adult food resources are available. It is secure across its range (G5 globally) and is not of conservation concern, though its Ontario populations are limited by the rarity of its host tree.

Host Plants

Larvae feed exclusively on hackberry trees. The relationship is obligate — no alternative host plants are used.

• Dwarf Hackberry (Celtis tenuifolia) — primary Ontario host
• Common Hackberry (Celtis occidentalis)
• Other Celtis species across the range

Habitat

Found in association with hackberry trees in a wide range of habitats: dry, rocky savannas, moist bottomland forests, woodland edges, near water, and in urban and suburban areas. In Ontario, the species is tied to the distribution of Celtis tenuifolia — one of the province's rarest trees — and is correspondingly rare. The species is secure globally (G5) and is not listed under any conservation legislation.