The Wingless Fly

Continuing the zoological theme, perhaps one of the most unusual beasties I have come across here is a wingless fly.

A valley in the north-west of the island boasts a hydroelectric system built in colonial times. At an altitude of 600 metres, water is diverted from stream into a man-made channel or aqueduct that runs for several kilometres before dropping down a metre-diameter pipe to two turbines and back into what has now become a river. Most of the water channel is covered with concrete slabs but on its way to the chute it passes through eight tunnels carved through the mountainside where the channel is uncovered. The tunnels vary in length but are divided by a waist-height concrete wall between the water channel and a pathway. Needless to say, this concrete wall has developed leaks and the pathway can be muddy at best, and at worst gives you distinctly wet feet.

One of the tunnels is home to a colony of bats with their associated guano, smell and fauna (including a giant gecko).

I took some friends for a hike along the aqueduct - it´s a fantastic walk. The views of perhaps our largest and deepest valley are spectacular. As you just walk along the 600 m contour, it is not physically very taxing in a country noted for its extreme relief.

We got to the bat tunnel and the pathway floor was flooded ankle-deep so my friends decided to edge along the top of the dividing wall using their hands to the roof to maintain balance.

Having passed the bats we returned to daylight ... I had wet feet, but they were covered in little beasties which provoked revulsion and had to be picked off one by one. I have never seen a group of humans acting so much like mutually grooming primates!

But I got to looking at these creepy-crawlies - they ran around like little jumping spiders, but surely they couldn´t be - they only had six legs!

What the hell are they?

I had some collecting tubes and alcohol with me so pickled a few which I then sent to a friend who works at London´s Natural History Museum ...

They turn out to be Wingless Flies (order Diptera) parasitic on bats! Obviously, they no longer need the power-of-flight (the bats do it for them!). In a tightly-packed bat colony they just crawl or jump from bat to bat. Fascinating! Evolution in action!

As the hike involved returning along the same route ... everyone got wet feet!