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Dragonfly cloud

April 30, 2017

 Cloud of dragonflies swarming in a Dar es Salaam garden - photo by Anne Outwater
The black dots in this photo are some of the 500 dragonflies in a cloud like swarm. 
They have been cleaning the air of mosquitoes for several days in Mikocheni-B, Dar es Salaam.

 

I wish I could share with you the view from my balcony in Dar es Salaam. It looks right over my pocket-sized nature reserve.  The sun was dipping towards the horizen so I came out to close the gate of the grill against the night, and I stayed for some hours.  I  pulled up a chair and put my feet on the balcony rails leaning back to watch the phenomenon above me.  I had never seen it before. 

 

It was a cloud of dragonflies (Sw. ngereng’ende). Of course I have seen many dragonflies. They live all over the world.  They are not uncommon.  But I’ve always seem them one by one.  Or several around a body of water. But I’ve never seem them as a cloud.  Or maybe I have and didn’t register it, or realize it.

 

But here was a cloud of dragonflies in front of my balcony. They were big enough (body length about 8 cm) and close enough that I could even see their wings fluttering. Their wings are separate, two on each side of the body, which they can operate individually. I could see the individual wings.

 

They were flying about 10-15 meters above the ground, darting back and forth.  Occasionally one made a loop de loop spin but mostly they were darting forward about 3-5 meters and changing directions swiftly almost as if they reached the end of something. The way they dart, they almost look like needles sewing thread. Making fabric from the air.

 

I am trying to count them but it is so difficult. They are very strong fliers. They change direction so abruptly that my eyes can’t quite follow them – my sight travels forward on the trajectory they were on, while they have already cut to another direction. It is difficult to count the individuals in the group.  

 

I took a couple of photos, trying to freeze their movement into a moment, then counted and multiplied the number by the space. It was hard to take a photo because the camera couldn’t focus on them.  So I focused on a coconut tree frond and then expanded the photo to the air in front of it. There are more than 120 black dots in the photo. Since the photo showed just a portion, multiplying the area to include the rest of the swarm, I could estimate there are maximum 500 in all.

 

Dragonflies are fierce predators, so it is lucky to see them.  As larvae they can keep a pool clean of mosquito larvae, and as adults they catch mosquitoes mid-air and dine on them.  They are efficient predators.  As both larvae and adults they use a basket to encircle their prey and bring it to their mouths to eat.  As larvae they have a jaw-like mask that they can spread in front of their face and bring in prey to their mouths. As flying adults they capture their prey, say a mosquito, mid-aid with the six legs which encircle the victim as in a basket.  The dragonflies then dine on this meal mid air.

 

So the area around a dragonfly swarm like this can be expected to be free of biting insects.  And in truth as I sit here, I am not getting bitten by the pesky grass mosquitoes we have here at this season.

 

Swallows were flying above.  And it did not seem by their smooth movements that they were eating the dragonflies.  The House Crows were flying to their night roosts through the cloud, not pausing.  Twelve yellow footed egrets flew over, and then a second flock of eight were heading south to spend the night in their rookery, perhaps at the mangroves guarding the Selander Bridge.

 

The East African birds most famous for traveling with and liking to eat dragonflies, are Amur Falcons.  That could mean, one day, I will see Amur Falcons in the garden, something else I do not think I have ever seen, but would love to. 

 

And as I mused about that possible event, the dragonflies, suddenly vanished.  I got up and looked around, and saw them in a cloud towards the setting sun as if to catch the last rays. 

 

Where they spent the night I do not know.  But this morning they are in a cloud over my neighbor’s roof. Hopefully they will eat all the mosquitoes.

 

 

From Anne Outwater's Nature Notebook

 

Wandering glider or Globe skimmer dragonfly (Pantala flavescens) By Muhammad Mahdi Karim in Dar es Salaam
- Own work, GFDL 1.2, https://commons.wikimedia.org/w/index.php?curid=7082460

 

 

 

 

 

 

 

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