The adults of H. illucens measure about 16 millimetres (⁵⁄₈ in) long.
These  medium-sized flies have a predominantly black body, with metallic reflections ranging from blue to green on the thorax and sometimes with a reddish end of the abdomen.
The second abdominal tergite has translucent areas, from which the specific Latin epithet derives.
The head is wide, with very developed eyes.
The antennae are about twice the length of the head.
The legs are black with whitish tarsi.
The wings are membranous; in the resting time, they are folded horizontally on the abdomen and overlapped.

H. illucens is a mimic fly, very close in size, color, and appearance to the organ pipe mud dauber wasp and its relatives.
The mimicry of this particular kind of wasp is especially enhanced in that the fly's antennae are elongated and wasp-like, the fly's hind tarsi are pale, as are the wasp's, and the fly has two small transparent "windows" in the basal abdominal segments that make the fly appear to have a narrow "wasp waist".
Black soldier fly larvae can be differentiated from blowfly or housefly larvae by a thin gray-black stripe on their posterior ends.
The adults of H. illucens measure about 16 millimetres (⁵⁄₈ in) long. These  medium-sized flies have a predominantly black body, with metallic reflections ranging from blue to green on the thorax and sometimes with a reddish end of the abdomen. The second abdominal tergite has translucent areas, from which the specific Latin epithet derives. The head is wide, with very developed eyes. The antennae are about twice the length of the head. The legs are black with whitish tarsi. The wings are membranous; in the resting time, they are folded horizontally on the abdomen and overlapped.
H. illucens is a mimic fly, very close in size, color, and appearance to the organ pipe mud dauber wasp and its relatives. The mimicry of this particular kind of wasp is especially enhanced in that the fly's antennae are elongated and wasp-like, the fly's hind tarsi are pale, as are the wasp's, and the fly has two small transparent "windows" in the basal abdominal segments that make the fly appear to have a narrow "wasp waist". Black soldier fly larvae can be differentiated from blowfly or housefly larvae by a thin gray-black stripe on their posterior ends.
Hermetia illucens