eTawau > Insects of Borneo > One pair of wings > Flies > Robber flies

Diptera: Asilidae

Robber flies (Asilidae)

Field records from Tawau, 2006–2012

The family names on this page are the photographer's own, from his old fly pages; they have not been checked by a specialist or on iNaturalist. Dates come from the camera or from the date printed on the photograph.

Robber flies are predators. They wait on a perch, dart out to catch other insects in flight with their strong, bristly legs, and stab the prey with a stout beak. Most have large eyes, a "beard" of bristles on the face, and a long tapering abdomen.

Order Diptera · Family Asilidae (robber flies, also called assassin flies) · genus and species not determined.

15 and 20 September 2006 — with prey

A robber fly seen from the front with large green eyes and a bristly face, holding a small prey in its legs.
15 Sep 2006, 15:34, face to face, holding prey.
A grey robber fly with a long abdomen perched on a twig, holding prey.
15 Sep 2006, 15:37, on a twig with its prey.
A grey robber fly with green eyes and long legs perched on a green leaf tip.
20 Sep 2006, 08:07, perched on a leaf tip.

Canon PowerShot A410. In the photographer's words on his 2006 page: "Location: Kampong Merotai, Tawau, Sabah … Photographs on 3 different days in September 2006 … Size: 1.5 cm. This Robber Fly wasn't all that concerned about me taking its photographs."

20 and 30 September 2006 — the "yellow bulb"

Close-up of a robber fly thorax with a small pale yellow knob circled behind the wing base.
20 Sep 2006, the yellow knob circled.
A robber fly side view with an arrow pointing to a small yellow knob below the wing.
30 Sep 2006, the same knob on another view.

The photographer wrote at the time: "When I noticed from the photos the Yellow Bulbs beside the abdomen of this Robber Fly my first thought was they are yellow flower pollens … So this yellow BULB is not pollen not fungus. But what they are?" The photographer circled a small yellow knob behind the wing. In flies the hind wings are reduced to a pair of club-shaped balancing organs, the halteres, and this knob is probably one of them. It is the reason flies are filed under one pair of wings. These two dates come from the file names; the copies carry no camera data.

8 December 2006 — ten robber flies in the backyard

A robber fly with green eyes holding an insect with its legs and beak.
8 Dec 2006, 10:17, feeding.
Close circular view of a robber fly head with its beak in a small insect.
8 Dec 2006, close-up of the beak in the prey.
Close circular view of a robber fly holding a hairy prey insect.
8 Dec 2006, 10:26, another fly with prey.
Two robber flies joined end to end on a leaf.
8 Dec 2006, 10:00, a mating pair, end to end.
A pair of robber flies mating on a green stem.
8 Dec 2006, 10:03, the pair from the side.
A pair of mating robber flies seen from above.
8 Dec 2006, 10:03, the pair from above.

In the photographer's words: "8th December 2006 is a bright hot sunny day, not less than 10 Robber Flies in my backyard garden. For couple of weeks I could not seen a single of them, now all at once, that many Robber flies appeared in a same day. The very same day I saw 3 of them with prey, and for the first time I watched a mating pair." The old mating page named the pair Ommatius; that genus has not been checked.

9 December 2006

A grey robber fly with green eyes and a long abdomen perched on a grass blade.
9 Dec 2006, 09:44, a grey robber fly.
A dark, almost black robber fly standing on a leaf.
9 Dec 2006, 09:41, a dark robber fly.

Canon PowerShot A410, the morning after the backyard count.

22 February 2009 — Taman Semarak

A small grey robber fly with orange legs perched on a green grass stem.
22 Feb 2009, 16:39, on a grass stem.

Canon PowerShot A470. Taman Semarak, Tawau.

8 December 2012 — Merotai, with prey

A brown robber fly with green eyes on a weathered wooden post, holding prey under its body.
8 Dec 2012, 11:32, on a wooden post.

Canon PowerShot A480; four frames in nine seconds. The prey is held under the body and is not identified.

Related: Flies of Borneo · One pair of wings · Insects of Borneo
Photographs © Wong Fook Yee. The 8 December 2006 account is the photographer's own words from his old page. Family facts: Wikipedia articles on each family. Page written 14 October 2026.