Midges, mayflies flock to the light

You wake up in the morning to find the walls of your house covered in large numbers of flying insects.

The cause: you have left the porch (or home entrance) light on overnight and flying insects are everywhere, settled all around the light.

At first the sight can be quite alarming. Swarms of mosquitolike insects are everywhere. These insects are non-biting midges and/or mayflies. They resemble mosquitoes which contributes to confusion with identification. While they certainly resemble mosquitoes, neither will bite or cause disease to humans. Even more significantly, mosquitoes are not attracted to light whereas these little insects certainly are. Commonly found in our area is Chironomus zealandicus (common name: New Zealand midge) and/or mayflies which belong to the class (or order) Ephemeroptera. Both insects can be found in large numbers, especially if living near a water source. This is because both midges and mayflies share a commonality: most of their life cycle (the larvae) is spent living in water. We do not normally see this larval form; we see the winged adults after they have emerged from their watery environment as flying insects.

There are more than a dozen different species of midges and approximately 40 to 50 species of mayflies in New Zealand. Both insects tend to swarm in large numbers; however, this does depend upon temperature, humidity and wind direction.

Midges are found in slow or stagnant water. In fact, their larvae are bio-indicators of poor water quality and water that suffers from pollution. Midges breed in large swarms and the adult midge lays up to 3000 eggs at any one time. Eggs normally hatch within two to seven days. The larvae have a distinctive reddish colour often referred to by fishermen as “blood worms”. The red colour is due to their blood being high in iron and oxygen binding proteins which is highly significant for midges as it ensures their survival in polluted low oxygenated habitats. Larvae begin life by burrowing into the substrate of the lakebed. They build a tube of silt that will become their home for the next two to seven weeks as they feed off various algae and detritus. They remain in this form before pupating for about three days and finally emerge as adult lake midges. The whole lifespan can be completed in a couple of weeks; however, as an adult their life stage is very short, only lasting three to five days. At this stage they do not eat, instead they are interested solely in breeding before they die.

In direct contrast, mayflies only survive in clean, highly oxygenated, running water. Structurally their larvae possess gills for breathing and a tail for swimming. They are very capable and swift swimmers. Water quality is essential for mayflies. Even just the slightest water pollution can cause juvenile mayflies to develop respiratory difficulties. In comparison to the lifespan of midges, mayflies live longer. An immature mayfly (called naiad) lives up to a year in the water. It is only as a winged adult that life is considerably shorter, from only a few hours to a couple of days depending on the species.

There is merit in thinking these two aquatic insects (both midges and mayflies) can (and do) go a long way in helping us to gauge water quality and levels of aquatic pollution within our local area.

If midges and/or mayflies are causing a problem at your place, a simple solution is to change the colour of your lightbulbs from white to yellow lights. Do not keep porch lights turned on continuously at night and keep window blinds closed so internal lights don’t attract them.