(My understanding is that) Humans at present do not have sufficient mastery of the natural process to create an animal or insect from scratch.
In theory however, our knowledge of evolution and genetics raises the possibility of being able to engineer a species (such as a fly) based on manipulating the genetic code. The power of science is being able to take a natural process and harness it for human purposes. We look at the shape of a birds wings and may discover the laws of thermodynamics- so eventually we may be able to reproduce the "lift" for a man made object.
Here's leonardo Da Vinci sketch of a birds wing:
Here's a sketch he made for a flying machine based on trying to identify the structures in a birds wing (or a bats wing), such as bones and feathers:
In the case of evolution we have already manipulated the process to an extent by using breeding, such as breeding chickens for increased meat yield. This process was already under way in the agricultural revolution in the 18th and 19th century. Darwin called it "domestic selection", the man-made eqivilent of "natural selection".
The leap darwin took was borrowing the mechanism of competing for resources to understand changes in population from thomas malthus. Malthus' theory of population was originally intended for understaing the limits of food supply on humans. Darwin applied it to animals as the mechanism of "natural selection".
Now- the same principle of understanding and reproducing a natural process by science can be applied to the "origin of species". For example- we cloned a sheep in 1996:
https://en.m.wikipedia.org/wiki/Dolly_(sheep)
The difference between artifically cloning an animal and altering the genetic code (at a guess) is an order to magnitude of control over the process. Its not technologically impossible.
Now, lets take your scenario for a second. Assume all life on earth (excluding yourself) died out. With enough time, resources and knowledge it is
possible to genetically engineer life. Its a physical process and we can theoretically repeat it in a laboratory. The process of abiogenesis is the one in which non-organic matter is turned into living organic matter. Hypothetically, we could eventually do it in a laboratory.
https://en.m.wikipedia.org/wiki/Abiogenesis
The wonder of genetics is that all life on earth is essentially built from the same genetic building blocks. Manipulating the genes of a fly, you could reverse engineer species from genetic material, or perhaps produce new species of fly or maybe another species entirely using the same building blocks.
This is an atheists view (a pretty radical one maybe) but not one based on being intimately familiar with the deatils in biology. my understanding is what you are asking is not impossible, but still technologically maybe a few decades away (and raises alot of ethical questions about how we use these technologies). But its not impossible.