Beetle or Fly? Why not both?

I have been busy in the archive, working on many different projects, but the most recent thing that has interested me while working at BIO has been the beetle fly.

BIOUG16313-G05 from top
BIOUG16313-G05 from top

Collections taxonomist Valérie Lévesque-Beaudin identified an Acelyphus politus that belongs to the family Celyphidae, commonly called beetle flies, from Malaysia in the Global Malaise Trap Program. The name Celyphidae comes from the Greek word “κέλνφος” meaning pod, shell, or case. There is very little known about this specific family of Diptera (flies), as it has not been frequently studied and is so profoundly different than its sister-groups. It is unknown as to why these flies have developed a beetle-like shell, although it is thought to be impacted by their environment. This insect is not found on the North American continent, but rather found in Oriental and Afrotropic biogeographic regions. There are roughly 90 species of beetle flies found around the world.

Celyphidae are small to medium-sized flies that can be easily recognized by their enlarged scutellum that creates their shell, similar to the beetles. The convex scutellum forms a protective shell over the abdomen and the wings. It is unknown as to why these flies have the extended scutellum similar to a beetle. Some sources say that the scutellum is speculated as a buoyancy apparatus to sustain aid in flight while others speculate that there is no real purpose, being merely accessory or ornamental.

Acelyphus politus collected in Malaysia from Global Malaise Trap Program
Acelyphus politus collected in Malaysia from Global Malaise Trap Program

 

Typical beetles fold their delicate wings under the elytra, the hardened forewing, while not flying and unfold their wings before takeoff. Muscles attached to the wing base operate the unfolding and folding of the wings. Beetle flies may have lost some flight capability as the enlarged scutellum would likely impair their wing movement, although it is still able to fly. At rest, the beetle fly’s wings are folded beneath the scutellum and almost completely covered, giving the fly its beetle appearance. Their shell does not open to allow wing movement, unlike a typical beetle.

Beetle fly from the front: mandible, maxilla, labium, and labrum
Beetle fly from the front: mandible, maxilla, labium, and labrum

The Aclyphus species, which is photographed here, have a narrow distribution in the Oriental region, primarily being Indomalayan and can be distinguished by their superficial characters. The texture of the scutellum is a useful superficial taxonomic character. It is variable between species and consistent enough within species, albeit not enough for species determination. Many Celyphidae are shiny and metallic in colour, although colour is variable and an unreliable indicator.

This species is saprophagous, meaning the larvae develop in or on soil while feeding on dead leaves or decaying grass, therefore the adults are found along riversides, streams, and in wet grassy areas, as this is favourable spot for decaying matter.

It would be interesting to know why this fly evolved to look like a beetle, and what its flying capability is with this structure present. What are the advantages, as a fly, to look like a beetle in this region?

BIOUG16313-G05 from the underneath
BIOUG16313-G05 from the underneath

Insects are so interesting because the line between orders (Diptera and Coleoptera) seemed to be slowly blurred through mimicry that is displayed in species like this one. Through learning about the family Celyphidae, my passion for insects has grown exponentially. Being able to work with such fascinating specimens on a regular basis has been a privilege that has broadened my appreciation for insects.

I hope you learned a bit about these captivating insects. Thank you for reading.

– Kylee

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