Stalk-eyed Signal Flies

Stuart Humphries

Australian Museum

Australian Museum
Sydney, Australia

Stalk-eyed Signal Flies, Achias spp.

Where do they live?
These unusual-looking flies occur mainly in New Guinea (with more than 90 recorded species) and in Queensland (with five recorded species).

What is their habitat?
The flies can be found in rainforests on shaded tree trunks.

What’s special about them?
These flies have their eyes on stalks, which serve some very useful purposes. First, the eyes give the fly superior vision, even enabling the owner to peep around corners. Second, the stalk can be used as a weapon to push competitors away and, third, the longer the stalk and the more wide-set the eyes, the stronger the signal to female flies that this male is big and strong and genetically a good catch.

What do they eat?
These flies eat the faeces (poo) of mammals and humans and also tree and plant sap.

How do they reproduce?
Very little is known about their reproduction.

What else do I need to know?
The flies are small and brown and, true to their name, the males have eyes on long stalks extending from either side of their heads. The females are without eyes on stalks. When the flies settle on a tree trunk they regard it as a place for courtship and their own territory which must be defended against rivals. When fighting face to face, rival males judge their opponents' size and strength from their head width. The clear difference in head width allows weaker flies to back off early and avoid possible injury.

Where do they fit in the tree of life?
Genus: Achias
Family: Platystomatidae
Order: Diptera
Class: Insecta
Phylum: Arthropoda
Kingdom: Animalia

What is their conservation status?
The Stalk-eyed Signal Flies has not yet been assessed for the IUCN Red List and there has been no targeted conservation work undertaken locally. However increased destruction of its favored habitat by logging and other activities could place it under threat.


  • Title: Stalk-eyed Signal Flies
  • Creator: Stuart Humphries
  • Publisher: Australian Museum
  • Rights: Australian Museum

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