Asterocampa celtis

Description

The Hackberry Emperor (Asterocampa celtis) is a medium-sized, brown butterfly in the brush-footed family (Nymphalidae), subfamily Apaturinae — the emperors. Its wingspan is approximately 4.5-6 cm. The upperside is a warm, variable brown with a row of black eyespots along the outer margin of both wings and several white spots near the tip of the forewing — a key feature distinguishing it from the closely related Tawny Emperor (A. clyton), which lacks these white forewing spots. The underside is patterned in muted greys and browns, providing excellent camouflage when the butterfly rests on tree bark, where it is most often encountered. Males are slightly smaller and darker than females, with more slender wings.

The species ranges across eastern and central North America, from southern Canada to Mexico, and is found wherever hackberry trees (Celtis spp.) grow — its exclusive larval host genus. It is one of the few butterflies that is commonly observed in urban areas, where planted hackberries serve as inadvertent host trees. The species is secure across its range (G5 globally) and is not of conservation concern.

The Hackberry Emperor is ecologically unusual in several respects. Adults rarely visit flowers — a striking departure from the nectar-feeding behaviour of most butterflies — instead obtaining nutrients from tree sap, rotting fruit, carrion, dung, and even human sweat. This feeding strategy classifies the species as a "cheater" in ecological terms: it extracts resources from plants without providing pollination services in return. The larvae are gregarious in their early instars, feeding together on hackberry foliage before dispersing as they mature.

Lifecycle

Two broods are produced each year across most of the range, with adults on the wing continuously from May through September. Females lay pale greenish-white eggs in clusters of 5-20 on the underside of hackberry leaves — a fecundity strategy that reduces the time and energy required for searching between oviposition events. Young larvae feed gregariously on the foliage, skeletonizing the leaves. As they mature, they become solitary.

The half-grown larvae from the second brood descend from the tree in autumn and hibernate through the winter within the fallen leaf litter beneath the host tree — a critical dependency on undisturbed ground conditions. In spring, they climb back up the trunk to resume feeding. Pupation occurs on the underside of hackberry leaves; the chrysalis is dark green with white spots and diagonal white lines. Adults emerge in early summer (first brood) and late summer (second brood). Males perch on trees, rocks, or fallen branches, particularly along streams, from afternoon until sundown, darting out to investigate any passing butterfly or other movement.

Ecology

The Hackberry Emperor is entirely dependent on hackberry trees for its survival — no other host plants are used by the larvae. This obligate relationship makes the conservation of hackberry populations, particularly the rare Celtis tenuifolia in Ontario, a prerequisite for the butterfly's persistence in the province. Where hackberries are present, the butterfly is reliably found, even in heavily developed urban and suburban landscapes — a testament to the species' ecological resilience and its ability to exploit planted trees.

Adults feed on a remarkable range of non-floral resources: fermenting tree sap from hackberry wounds, juices from rotting fruit, animal carcasses, dung, and the sodium-rich sweat of humans. When the butterfly does visit a flower — a rare event — it uses only the proboscis, never allowing its feet or antennae to touch the reproductive structures. This "cheater" behaviour means that even when floral resources are used, no pollination occurs. The species is essentially a parasite of its host trees, extracting nutrients from sap and foliage without providing any known ecological service in return beyond its role as prey for birds, spiders, and insect predators.

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 wherever hackberry trees occur, from dry, rocky savannas and limestone barrens to moist bottomland forests, urban parks, and residential neighbourhoods. The species is tolerant of a wide range of conditions and is often found near water, along streams, in woodland edges, and around buildings. In Ontario, it is associated with the rare dry savanna and barren habitats where Celtis tenuifolia persists, though it may also use planted or naturalized Common Hackberry in urban areas. The species is secure globally (G5) and is not listed under any conservation legislation.