Creature of the Month – Robber Fly

Robber flies belong to the Asilidae family within the order Diptera. Like all true flies, robber flies have only 2 wings.  They also have a distinctive hollow space between their 2 large compound eyes which distinguishes them from most other kinds of flies.  They are powerfully built with stout, spiny legs and a dense moustache of stiff bristles on the face.

(A common robber fly)

(A common robber fly)

Robber flies are particularly abundant in sunny, dry habitats. They are generally found in forested areas such as Venus Drive, Lornie Trail, Bukit Timah Nature Reserve, Central Catchment Nature Reserve, etc. According to the Book “Singapore Biodiversity: An Encyclopedia of the Natural Environment and Sustainable Development”, at least 17 species have been recorded in Singapore.

(Female & Male of another common robber fly species)

(Female & Male of another common robber fly species)

Over the years, I have seen and photographed a few robber fly species but, sadly, despite my effort searching over the internet, I am unable to identify the species names of these aerial stunt flyers. Here are some not so commonly found species.

(Uncommon robber fly species)

(Uncommon robber fly species)

The most attractive robber fly species in Singapore, in my opinion, is the Ommatius sp. As far as I know, there are only 2 persons who have photographed this rare robber fly in Singapore. My friends, Rey Aguila shot one at Pulau Ubin in 2007 and Allan Lee captured it at Venus Drive last week. I had only seen it once in Malaysia at Endau Rompin State Park. It was very skittish and flew off after I took a few shots.

(A rare robberfly)

(A rare robberfly)

The name “robber flies” reflects their notoriously aggressive predatory habits where they attack in flight and feed on mostly on other flying insects such as wasps, bees, moths, beetles, plant hoppers, grasshoppers, dragonflies, etc.

IMG_7562

(A robber fly having breakfast)

Robber flies wait patiently on branches or logs and rush out to attack when suitable prey flies by. They use its bristly legs to intercept the prey by grasping it around the head or back. They then make use of its strong proboscis to inject the victim with saliva containing digestive enzymes that paralyze the victim and liquify the insides. The robberfly then suck the juicy meal through its proboscis. These images below show how good they are in catching a wide variety of preys.

(Robber flies with various preys)

(Robber flies with various preys)

Although robber flies are one of the most formidable predators in the insect world, they are sometimes prey for other larger creatures such as birds, spiders, assassin bugs, praying mantids, and even other bigger robber flies as shown below:

(Robber fly eating robber fly!)

(Robber fly eating robber fly!)

Some people may be interested to know whether robber flies bite human?  Under normal circumstances they don’t unless by accident or if provoked.  I have seen many robber flies in the wild but have never been bitten before.

Robber flies exhibit minimal courtship behavior. Instead, the male pounces on the female much like an act of prey acquisition. Copulation is accomplished in a tail-to-tail fashion with the male and female genetalia interlocked.  Flight is not completely inhibited during mating. Similar to dragonflies, the duo has no trouble flying around in this condition ie. the male generally towing the female backwards.

(Robber flies in love!)

(Robber flies in love!)

Robber flies mating are rather difficult to find.  I was therefore very excited to spot a pair at Zhenghua forest last year but they flew off and disappeared before I could position my tripod. About an hour later, I found this pair about 10 metres away from where I sighted the earlier ones. Could these be the same pair? If yes, then robberflies mate for a long period!  I shifted my tripod a little and it surprisingly produced two different backgrounds as follow:

(Same mating pair of robber flies but with different backgrounds)

(Same mating pair of robber flies but with different backgrounds)

From my searching of information on robber fly, I have the feeling that it is not well studied in Singapore or in South East Asia. But there are lots of information in the web written from other parts of the world.

References:
Singapore Biodiversity – An Encyclopedia of the Natural Environment and Sustainable Development
Wikipedia – the free encyclopedia

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