They procreate sexually, as far as anybody knows, much like elves, men, and dwarfs. According to the Silmarillion, Melkor (Morgoth to the Elves) would abduct and corrupt some of the Firstborn (the first Elves placed on Earth) in order to chastise his Valar "family"...
However, this does not explain how Morgoth was able to create so many orcs. Perhaps he used slave labor? Or maybe they just multiply really fast?
The Hobbit doesn't go into detail about this issue, but since it takes place before the beginning of the Second Age, when most modern fantasy races were created, we can assume that orcs were still evolving at that time. In fact, the earliest reference to orcs we have is from a poem by Taliesin, which dates back to around AD 600. So they probably didn't exist in large numbers yet.
In any case, whether they reproduced like humans or not is irrelevant to the story; what matters is that they are evil and want to destroy everything good and innocent.
In-fiction origins Tolkien wrote in The Fall of Gondolin, "all that race were bred by Melkor of the subterranean heats and slime." Orcs are East Elves (Avari) who were enslaved, tortured, and bred by Morgoth (as Melkor came to be known); they "multiplied" like Elves and men. In order to defeat Morgoth, a union was formed between some of his captives and Vala elves, which produced a new people: the Noldor.
Tolkien later confirmed this interpretation in a letter written in 1969: "Orcs were evil spirit beings whom Morgoth had created. Their origin is called the 'Fall of Gondolin.' They were the most terrible enemies that the Noldor ever faced...When Gondolin was destroyed by fire from the Air, many Orcs escaped into the wastelands of Middle-earth where they remained free for a time."
In a 1965 interview with John Quinn of The New York Times, Tolkien explained that Orcs were "evil spirits brought up by Morgoth [i.e., Satan] from the depths of Hell".
According to The Book of Lost Tales, orcs were "formed from the heats and slimes of the ground" by Morgoth's wizardry. Again, Tolkien revised this later since Morgoth could not produce life on his own. This gave rise to the most widely held belief that Orcs were developed from tainted elves. However, in a letter written in 1973, Tolkien stated that this was only his interpretation of how orcs came into being and that they might have been created by other means such as "fireballs from Palantir", "angels with evil intentions", or even "dwarfs".
In War of the Ring, it is revealed that Sauron bred orcs to serve him. They are described as "evil creatures, half-ogre, who live in darkness and eat anything that moves", which sounds like elf blood to me!
In LotR it is also said that Morgoth made some elvish women fall under his power so he could use them to breed new races. This is what caused the hatred between Orcs and Elves - before that time they were friends. Indeed, one of the earliest examples of friendship shown in literature is between two orc warriors who respect each other after a battle.
But anyway, back to our question...
Orcs are born ugly but can become handsome if given a chance. This is why many girls/women are attracted to orcs.
Saruman explains how the first Orcs were created, specifically by torturing and mutilating elves. That is the genesis narrative as told in the Silmarillion. The Uruk-Hai are bred in pods, similar to how fish are reared. The bodies develop in mud sacs until they are fully fledged men. Then they are taken out and given weapons with which to fight other Uruk-Hai.
In The Lord of the Rings, we are told that Orc blood tastes of iron and mud when mixed with human blood. This would make sense if they were born this way, but it's also possible that they are bred by Sauron to be violent and foul-tempered. He could even be using this knowledge of Elves' torture methods to create new breeds of Orc to do his bidding.
There are two types of Orcs: green and black. Green Orcs are used for fishing duties and farm work. They like to live in forests. Black Orcs serve either as guards or warriors. They like to live in cities. There are more black than green Orcs because they are more useful to Sauron. However, both types of Orc are tortured and mutated by Sauron to serve him.
It is possible that the origin story of the Elves and the Orcs is different in each book/storyline. But since we only have information about them from The Lord of the Rings, this article focuses on what Saruman says in that context.
Earthworms sexually reproduce by aligning their bodies and sharing sperm. Polychaetes, on the other hand, which are usually marine, reproduce asexually. One method is fission, which occurs when the worm creates a perfect duplicate of its DNA and then separates into two. The new individual has the same genetic makeup as the parent.
Another method is called "budding." In this case, part of the body wall splits along with some internal tissue to create a new individual who will eventually join the group of his or her own species. Earthworms use this method to divide in order to create clones of themselves that will grow into new worms. Humans also use this technique to produce twins or multiple births. It's also how tumors form because they are clusters of cells that have divided without control of growth signals.
Polychaetes can reproduce asexually by dividing at the molecular level. A fragment of their body wall divides into two new individuals that will continue to live and eat just like the original. These fragments may be small pieces of tissue or larger segments of the body wall. Some polychaete species can even regenerate entire organs such as intestines or lungs!
Some organisms, such as algae, reproduce by cloning. This means they split into two identical copies of themselves without merging with another organism. Algae usually clone by forming buds that break off to become independent plants.
Gorons are asexual and all-male creatures that reproduce through budding. They grow plants with seeds that contain all the information needed for new gorons to develop.
When one of them finds something interesting, they give it a good sniffing over. If they like the smell, they pluck some of the plant's leaves or flowers and eat them. This produces an intoxicating effect that makes them feel happy and excited! As soon as they recover from this effect, they go in search of more plants that they can eat. This process will be repeated until either the goron dies or finds another plant that it likes better. Gorons only eat plants that grow in Pandora's Realm because they don't exist anywhere else on Earth.
Since there are no females among the gorons, they use their intelligence to invent things that humans need. For example, they made tools used by hunters to catch animals for food. Some gorons work as traders; they travel around on the back of a griffin or dragon and sell their goods in towns and cities. Others take care of human beings. Some go as bodyguards for very important people while others work in hospitals. There are still other gorons that study science or technology and help humans understand how things work.