Biodiversity Fact File: Manx Robber Fly

Monday 4th April 2016

Part of our series of biodiversity fact files looking at species that appear locally and are considered "at risk"

The Manx robber fly (Machimus cowini), which was first recorded in Douglas in the 1940s, is named after Manx naturalist, Will Cowin.

The fly’s favoured habitat includes soft grass verges and soft cliffs along the north and north east coast of the island, and sightings have also recorded in the Ballaugh Curragh. However, the fly is not exclusive to the island as populations have also been recorded in Ireland.

Numbers have declined due to habitat destruction, with soft grass verges, such as the area in Douglas where they were first found, lost to road widening and other development.

The robber fly’s preferred food includes damselflies, bees, butterflies and moths, which it often hunts in the middle of the day, using the best available light.

Known as an assassin fly, due to its excellent hunting and brutal take down techniques, it lays still, on prominent leaves or rocks, near to open spaces, waiting for its prey to approach, then catches it in mid-flight.

Targeting such large prey seems to present no problem to this fly: It has five eyes, comprising of two compound eyes and three simple eyes, to help locate its prey. Then, once caught, the fly uses Its short bristly legs to hold it victim in a firm grasp before stabbing it with its proboscis, injecting a paralysing poison typically through easily pierced body parts such as the eyes and between the segments of the body.

To help protect it from its struggling prey, the fly has a thick, moustache-like, array of bristles on its head, called mystax.

With long and narrow wings adapted for speedy and aerobatic flight the robber
fly is suitably adapted for its lifestyle!

Isle of Man Post Office has twice featured the fly on a stamp, once in 1979 and again in 2001.

The Manx robber fly is an incredible creature, its habits would make a fascinating TV documentary!

More information

See a photograph and find out what the Manx Museum’s i-museum has to say about the Manx robber fly

Read about the Manx robber fly on Wikipedia

Want to try to spot a Manx robber fly? Look closely on our reserve at Cronk y Bing in Bride, and at the Ayres nature reserve

Find out more about our island's biodiversity

Tagged with: Ayres, Biodiversity, Cronk y bing, Nature reserves