Not only are flies dirty insects, but they also challenge the limits of human tolerance with their not-so-short "attacks". However, the life span of flies is extremely short, generally only seven days, can be said to be the world's shortest life expectancy of insects, their survival time is only about 10 days, but they have a long life cycle. Flies generally only seven days of life although flies and mosquitoes are two kinds of insects, but their lives are very short. Generally speaking, they only live about 7 days, because the female flies have to bear the heavy responsibility of reproducing, so their lives can be up to 30 days. Flies can reproduce up to 20,000 offspring in a lifetime. Although flies have a short lifespan, they are very efficient at laying eggs and reproducing. Although flies have a short life span, they are very efficient at laying eggs. Flies have the physiological characteristic that they can lay eggs for a lifetime after a single mating. This calculates that a female fly can give birth to more than 20,000 small flies in a lifetime, which is why we always think that flies can not be killed, because we think that if a fly is killed, then its life will be terminated.