Can flies become flies directly without passing through the larval segment and only laying eggs?

No, it must go through the larval stage.

This is a question that I would definitely break with conventional wisdom, but it is something I have seen with my own eyes. When I was a child, in the summer, there were a lot of flies in the house, and it was common to kill it. There was an experience that I still remember vividly, and I still think about it very clearly:

After eating, just after clearing the table, a big fly with a green head and green tail landed on it; I hate this green one the most, maybe it just came from the latrine——— before it could stand firm, I slapped it down, and when I raised my hand, I saw that a few small flies had been squeezed out of its tail, and I was about to use my fingers to flick it, but they didn't even turn over one of them, as if there was a suction on the side, and flew away from the table diagonally above. "Curious," I was startled and watched them fly away. When I looked at this fly again, it was still trembling, so I took its wings in the air, and gently pressed its dorsal abdomen, at this time, a string of small flies emerged from its tail, did not sink, but slowly flew away diagonally, like a scene of blowing soap bubbles, because their small green is no less than an adult fly, and the body also emits milky white fluorescence, and the visual sense of fluttering obliquely above is more colorful than soap bubbles!

This is what I saw when I was a child, so I'm sure of it: flies can also be produced directly from the mother, and even without the cumbersome front curve of feathering or anything, an adult fly can fly out with one wing.

Strictly speaking, flies lay eggs because their uterus is formed as eggs

However, flies' eggs often hatch early before they are expelled (which may also be affected by factors such as temperature).

Therefore, sometimes flies stop on food and feces, and some white and moving maggots will drop (disgusting to think).

And then there's the big, black fly that you can see all the time, and if you see it coming into your house, don't kill it, but get rid of it, and I've tried it many times, and after killing it, I saw the maggots crawl out -- and its eggs should be easy to hatch.

PS: All of the above are common flies. In fact, there are some species of the family Mesophilidae and the family Parasiticidae. Their eggs hatch early in the maternal reproductive tract, so they produce larvae directly, called pseudoviviparity.

Golden yellow, a little smaller than sesame seeds, are fly eggs.

Banana-shaped or oval-shaped, about 1 mm long, with two crests on the dorsal surface of the egg shell, the thinnest membrane between the crests, from which the larvae emerge when hatching.

The peak of spawning is at 17:00 to 19:00 every day.

The length of the pre-oviposition period (i.e. the time from emergence, to the first oviposition) of female flies is closely related to the ambient temperature: an average of 9 days at 15, only a few days at 35, and no eggs at 15 or less. After mating, female flies often crawl into the breeding crevices such as human and animal feces, and extend out of the ovipositor tube to lay eggs in the depths of the breeding organisms, so that the eggs can be fully protected by the silver jujube.

Development:

The development time of the egg is 8 24 hours, which is related to the ambient temperature and humidity, and the egg does not develop under the 13 or 13 holes, and dies if it is lower than 8 or higher than 42.

The incubation time of eggs decreases with increasing temperature in the following ranges: 22 hours, 20 hours; 25 hours, 16-18 hours; 28 hours, 14 hours; 35 hours, only 8-10 hours. The humidity of the growing substrate also has an effect on the hatchability of the eggs:

When the relative humidity is 75% and 80%, the hatching rate is the highest. Hatchability is significantly reduced below 65% or above 85%.