House fly, the one that bothers us at home!

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Photo credit: Fredrik Andreasson

When it comes to the most annoying insects, the housefly undoubtedly takes first prize. In fine weather, it invites itself into our homes, harassing us during meals or naps. This insect loves rotten meat, lays its eggs in feces and then lands on our food. The housefly is repugnant to us in many ways, but what do we know about it? About its habitat, its way of life, its reproduction? Is it dangerous for humans? Does it transmit diseases? Let’s get to know the most widespread Diptera in the world.

Who is the housefly?

The house fly (Musca domestica) is the most common of all flies. Like all Diptera, it has 2 functional wings, unlike bees for example (Hymenoptera), which have 4. The insect belongs to the muscidae family, made up of 5000 species, of which 450 live in Europe. Unlike dogs and cats, the fly is not man’s best friend and yet we call it domestic. The reason ? She willingly enters our homes (domus in Latin). The Diptera followed man to all regions of the planet and easily adapted, making it one of the insects with the widest range in the world.

What does the housefly eat?

In the larval state, Musca domestica feeds on decaying organic matter and excrement. In the adult stage, it is omnivorous. Lacking mandibles, the housefly cannot chew solid food, so it consumes liquid substances that it sucks up with its sucking-licking mouthparts, which resemble a proboscis. Their diet includes food waste, animal droppings, carrion, or rotten fruits and vegetables. To facilitate its digestion, the housefly deposits its saliva on the food in order to moisten and dissolve it, then it absorbs it in liquid form. The dipteran can also regurgitate partially digested materials to then reabsorb them.

How to recognize house flies?

The adult housefly measures 6 to 8 mm in length and its average weight is 10 mg, with females being slightly more massive than males. Musca domestica can be distinguished from other fly species by paying attention to the following characteristic features:

A body entirely covered in bristles; A grayish thorax adorned with 4 narrow black longitudinal bands; A gray abdomen dotted with 2 yellow spots; A pair of membranous wings, the second serving as balancers to allow balancing in flight; Compound (globular) eyes of reddish brown color; Mouthparts forming a proboscis which ends in 2 pads equipped with pores (through which the insect sucks its food); Short antennae composed of 3 articles, the last of which carries a long silk (arista). Where does the housefly live?

The housefly is probably the insect with the widest distribution in the world. It is present wherever man is found, and is found in all populated regions of Europe, Asia, Africa, America and Oceania. The fly is called a synanthropic insect, which means that it is capable of adapting to environmental conditions created or modified by human activity. In the city or in the countryside, the dipteran frequents all the places conducive to its reproduction and the feeding of its offspring: landfills, breeding farms, slaughterhouses… At night, when it finds refuge in our homes, the house fly sits on walls, ceilings, tables. This animal species has the ability to walk vertically using a mechanism called capillary adhesion. Its legs secrete a thin layer of adhesive fluid that allows it to climb and stand upside down on any surface.

What is the life cycle of the housefly?

In areas of the planet where conditions are favorable throughout the year (temperatures between 25 and 30°C, abundant food), the house fly can give birth to up to 12 annual generations which complete their life cycle in 2 weeks. The female usually mates only once and retains the sperm for future egg fertilization. In the space of 3 or 4 days, it can lay up to 600 eggs which it deposits in 5 to 6 clusters comprising 75 to 150 eggs. To summarize, the life cycle of the housefly is divided into 4 distinct stages: the egg, the larva, the nymph and the adult. Here are details of the different stages that mark the short existence of this dipteran:

The egg

The female lays oval, white eggs in moist organic waste, often animal feces, preferably exposed to light. The eggs are tiny (around 1 mm) and hatch in a few hours, between 8 and 24 hours depending on humidity and ambient temperature conditions;

The larva or worm

When hatched, the larva measures 3 to 9 mm long and is creamy white in color. It has a pair of dark mouth hooks with which it searches for food in feces, rotting plants or food remains. The worm must go through 3 molts to grow, each lasting between 3 days (in temperate temperatures) and 8 weeks (if the climate is colder). A fully developed larva is up to 1 cm long and has a smooth, yellowish-white body. It will then migrate to a drier and cooler place to pupate;

The nymph or pupa

In the nymphal stage, the insect resembles a capsule called a pupa. Initially yellow-orange in color, it becomes light brown then brown as it ages. Its skin hardens to create a protective shell, where the nymph can fully develop its body segments and appendages of an adult housefly. Pupation lasts between 3 days (at temperatures above 30°C) and 3 weeks, when the temperature is low (around 15°C). Just before emerging, the pupa sees a protuberance appear on its head which will help it break the shell and then disappear;

The adult

After emerging, the adult fly needs a few hours of drying before it can fly away. Arriving at this stage of its life, the dipteran displays a longevity of 2 weeks to 2 months, in good conditions. This short period is solely dedicated to reproduction and then the animal will die.

Are flies dangerous for humans?

Before seeing if the housefly is dangerous for humans, let’s highlight its important role within the ecosystem. Whether in the adult or larval stage, the Diptera is part of the food chain as prey for many insectivorous birds (swallows, swifts, sparrows, etc.), for spiders, amphibians (frogs, toads) or even for bats. The fly annoys us but as seen above, it actively participates in the decomposition and recycling of organic matter. By placing its proboscis in excrement, food waste and animal corpses, the insect is however a vector of a multitude of pathogenic elements such as bacteria, fungi, viruses and parasites. After being in contact with contaminated feces or infected food, the housefly can transmit certain diseases to humans, such as:

Dysentery; Salmonellosis; Typhoid fever ; Conjunctivitis; Diphtheria (cutaneous); Gastroenteritis.

To avoid contamination, it is essential to maintain good hygiene, especially in the kitchen, by systematically covering food, cleaning surfaces and emptying trash cans very regularly.

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