It was like a scene from an Alfred Hitchcock film. The sliding glass doors of my office were swarming with midges, commonly called lakeflies here (because they lay their eggs in nearby Te Waihora/Lake Ellesmere, and rise off the lake in huge swarms in summer). By their density (at least 1 per square centimetre), and the size of the doors, I estimated that there were at least 90,000 on the doors alone, not counting the ones swarming around looking for landing space.
I had been working late in the office, with the lights on, and they were attracted to the light. I turned off the light, took a deep breath (breathing in midges is horrible), and bolted out the door, slamming it closed behind me.
There were about a hundred on my ceiling in the morning. I reckon that was pretty good, given how many were knocking on the door.
I actually don’t mind the midges much. They don’t bite, and their appearances are brief, if dramatic.
But the question is, what are they all doing in those great big swarms? Well, the swarms are great big mating displays called leks. Male midges (they are the ones with feathery antennae), fly around in large swarms trying to attract the eye of a female. The females drop by the lek, pick out their favourite male, and mate with him. The resulting eggs are laid in slow-moving bodies of water (or sometimes on wet car parks, where I imagine they don’t live long).
The larvae of our particular midges are called bloodworms. They are one of the few insects that have haemoglobin in their blood. That’s what gives our blood its red colour, and it does the same to the midge larvae. The haemoglobin allows the midge larvae to live in low-oxygen, stagnant water, because it can capture and store oxygen, just as it does in our blood.
Midge larvae are a critical part of the food chain in many terrestrial aquatic ecosystems, feeding fish and other insects. They also must be important food on land, too. The spiders and songbirds certainly enjoy them when they swarm.
Still, in spite of their harmlessness and their ecological importance, I think Hitchcock could have had made a great movie of them.