Why do flies always like to "rub their hands"? They even twist their heads off to play with them? I was shocked after reading the truth...

Expert: Zhang Qikai, Chinese Academy of Agricultural Sciences, PhD in Insect Ecology

This article was reviewed by Wu Shengyong, Associate Researcher, Chinese Academy of Agricultural Sciences

When it comes to flies, most people's first reaction is dirty, unsanitary, and pests...

Although flies are hated by everyone, they also have an interesting side:

Sometimes flies will rip their own heads off for fun;

Flies will often fly around, then stop and start rubbing their hands;

…

Seeing this, everyone has a question: Why do flies have these strange behaviors?

Well, let me give you some basic knowledge today.

Can a fly twist its own head off for fun?

Why do flies twist their heads off? Just for fun?

This is actually not a common behavior of flies. It is more of an unconscious action. The fly may accidentally pull its head off while rubbing its hands or face. The fly may not even know that the thing in its hand is its head and will play with it for a while.

For most animals, they cannot survive if their heads fall off, but flies are insects. The circulatory system in their bodies is an open-tube circulatory system. Blood mainly flows between the heart, dorsal blood vessels, and various organs and tissues. Flies can breathe with their abdomens, so when the head is twisted off, the fly can only lose sight but can still move.

Since they have no head, flies cannot eat normally and can only excrete. Energy is continuously lost, and there is a high possibility that they will starve to death. They may also die from bacterial infection of the wound.

Why do flies like to rub their hands?

1. Clean your body

Each of the flies' claws has a hook and a pad. The hook can grab objects to support the body, while the glands on the pad can secrete lipid fluid to increase adhesion, which is why flies can hang upside down on smooth glass without falling.

Since flies have no nose, they rely on the taste and touch sensors in their legs to distinguish the taste of food. If their legs are covered with dirt, it will affect their judgment of food. In order to correctly distinguish the smell, they have to rub their hands and feet frequently to ensure the accuracy and sensitivity of their taste organs.

2. Helps with fast takeoff and obstacle-free landing

Flies also like to fly around. When they see something, they will pounce on it to taste it. Their legs are easily covered with various foods. In their spare time, they stop to rub their hands and feet to clean off the food, which helps them take off quickly and land without obstacles.

3. Attract males for mating

In fact, in the world of flies, female flies who can rub their hands and rub quickly are attractive. During the breeding season, female flies will release their sex pheromones by rubbing their hands. When they encounter male flies, they will speed up to attract males to mate with them.

Are all flies pests?

Of course not. In Australia, flies are beneficial insects that benefit the people.

This is because the sanitation conditions in Australian cities are good, and environmental changes have caused flies that originally lived in garbage to face extinction. As a last resort, they have moved to grasslands, forests and fields. Over time, flies have changed their past bad habits in the new environment and mainly survive on food juice, nectar and young leaves and wild fruits.

At present, Australian flies have become one of Australia's major commodities, used as experimental materials for scientific research units or as bait for fishing. American countries such as Brazil and Mexico also use them to make delicious insect food. More importantly, Australian flies work tirelessly to fly through flowers and grass, acting as "flower matchmakers", bringing huge economic benefits to local agriculture, and are called "God of Wealth" by people in the Australian grasslands.

In addition, scientists have found that flies have many sensors on their antennae, which makes them particularly sensitive to smell. An entomologist at Illinois State University in the United States once used the flies' sensitivity to blood and body odor to find the murder scene and calculate the time when the murder occurred.

People have also discovered that flies secrete an "antibacterial active protein" from time to time, and the effect of this active protein is much stronger than antibiotics developed by humans.

In this way, whether flies are beneficial insects or pests depends on how people use them.

Can you still eat food that has been touched by flies?

First we need to understand what flies do on your food. There are three main things:

1. Residual Pathogens

Flies have taste receptors on their feet, and considering that flies like to hang out in dirty and messy places like garbage dumps, their bodies and legs may carry pathogens, and as long as they come into contact with food, they may leave the pathogens on the food.

2. Vomiting and diarrhea

Flies have no teeth and can only spit out a mixture of saliva and digestive juices to digest the food first and then suck it into the stomach. If there are food particles that cannot be digested, the fly will swallow them with another straw first, and then digest them repeatedly with saliva until they can be sent into the stomach.

So, the fly will continue to repeat this process of vomiting, sucking, vomiting, and sucking again on the food.

3. Egg laying

An adult female housefly will lay eggs 4-6 times in the 2-4 weeks of its life, totaling about 300-900 eggs. It is very likely that food will be contaminated with fly eggs. Although the eggs do not carry pathogenic bacteria, they are also disgusting.

Food that has been touched by flies may have been contaminated with bacteria, vomit, eggs, and excrement. For the sake of health and safety, try not to eat food that has been bitten by flies.

How to effectively repel flies?

Drug prevention

The drugs used to control flies are mainly livelihood insecticides: organophosphate insecticides, carbamate insecticides and pyrethroid insecticides.

Coin drive

Prepare a transparent plastic bag, fill it with clean water, then throw a few one-dollar coins into it, tie the bag tightly, and hang it by the window.

Many small stalls in Hong Kong, Macau and Taiwan use this method to drive away flies. What is the principle behind this?

Because flies have compound eyes and are very sensitive, and water bags and coins can scatter light, which looks dizzy to flies. When we hang the water bag by the window, the flies dare not fly in.

Yellow board trap

Flies are attracted to yellow things, so you can hang a few yellow sticky insect boards at home to effectively eliminate flies.

UV light trapping

For thousands of years, insects have relied on the sun's ultraviolet rays to fly, and ultraviolet rays have a strong visual response in almost all insects. Studies on the complex electro-optical responses of many species of flies have shown that flies are most sensitive to the spectrum around 365nm, and ultraviolet rays at 365nm are harmless to humans.

Therefore, you can place a 365nm ultraviolet lamp at home, which can also have a good trapping effect.

Smell trap

Prepare a small bowl, add a spoonful of brown sugar, pour some beer, then cover it with plastic wrap, make a small hole on it, and you have completed a trap for catching flies.

Because flies will be attracted by the smell of brown sugar and beer, they will drill into the bowl and cannot get out.

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