Bucolus fourneti is a native Australian, small, hairy coccinellid beetle approximately 2.1-4.5 mm in diameter. It was described by Étienne Mulsant in 1850
Due to the persistence of three distinct colour morphs that are somewhat separated geographically, it was thought that it was actually three different species: Bucolous nuytsiae Lea, Bucolus nigripes Lea and Bucolus obscurus Lea. However, Slipinski and Dolambi (2007) have shown that the male genitalia and general external characters remain constant within the different geographical morphs and synonymised the three species to one.
Morphology
Adult
This ladybeetle has a typically rounded form and has three geographically separated colour morphs; light brown/grey with a red smudge on the middle of each elytra (wing casing), dark grey with a red smudge on the middle of each elytra, and dark grey with no red smudges or spots.
The head, elytra, legs and underside are entirely covered in small hairs. Though there has been no substantial evidence gathered, it has been preliminarily suggested that the morphology of this species suggests that it is a myrmecophile (tends to live in close proximity to ants/ant-liking) and it may possibly be a myrmecophage (ant eater).
Pupae
Length 3.1 mm, width 2.0 mm. The pupa is covered in a dense coat of white, waxy filaments that is relatively longer and denser than on the larvae. The filaments themselves are also thicker and longer than those of the larvae, and cover the dorsal surface only.
The pupae are creamy white without any apparent sclerotisation or colour pattern. The pupa is anchored inside of the last larval skin through the urogomphi. The larval exuvia, with the pupa inside, is attached underneath a piece of eucalypt bark. The entire body of the pupa is sparsely covered in a darker brown pubescence that is particularly longer and denser on pronotum. The body is segmented with eleven segments clearly visible: the three thoracic and eight abdominal segments. The body of pupa is broadly elongate with the pronotum flaring towards the mesonotum and the abdomen tapering to the terminal abdominal tergite. There are no spines anywhere on the body.
Head
The head is pale homogenously sclerotised and sparsely setiferous. The clypeolabrum is rounded and sits as a semicircle protruding down from between the large, prominent eyes; frontal part flat or weakly concave. Antenna is very short, extending to about one fourth of the distance between eye and the widest lateral margin of the pronotum; loose three-segmented club is distinctly visible; club does not have any spinules or setae. Maxillary palps well visible, last segment enlarged. The antennal segments are relatively spherical, and each antenna sits in the ventral groove along the inner margin of the eye. The eyes are approximately one eye-width apart.
Thoracic segments
The pronotum is distinctly transverse and moderately convex with its lateral sides widely explanate and extending rooflike over head and legs. Its anterior margin is straight, while the posterior one is slightly lobed medially. The elytron is homogenously and sparsely setiferous. The hindwings are glabrous. The legs are short and robust, tucked in close to the body with the forelegs tucked under the head, the midlegs tucked under the forelegs and the hindlegs tucked under the midlegs. The femora and tibiae of all legs are broad and dorso-ventrally flattened.
Abdomen
The abdomen is widest at the third tergite and curves laterally towards the ventral surface. The terga are sparsely setose with groups of longer and denser setae near the lateral corners; spiracles are not visible externally. Due to the curved abdomen, the single pair of urogomphi cannot be seen dorsally. The urogomphi are entire, unbranched and sit on the apex of the terminal abdominal tergite. They are relatively short, curving slightly inwards towards the ventral surface. The urogomphi end in a rounded club, with the club slightly wider than the stalks. These clubs are darker brown, particularly on the ventral surface, contrasting the rest of the body.
Larvae
The final instar larvae can be up to twice as large as the adult, and the second to fourth instars are known to be covered in thick, white waxy filaments.