Vulcans are monsters that use take over to turn people into monsters. They like women. In Fairy Tail, they are seen as perverted apes and appeared twice in the manga and anime.
Vulcans are perverted ape-like creatures who lust after women (so far child and up to adult) and food (IE: Happy's egg). Their power are using Take Over to turn people into monsters, using bare hands/ brute strength, or use weapons.
Vulcan(s), who are created by Hiro Mashima, have no current information on what inspires the author to create him.
In Fairy Tail anime, the Vulcans made 3 appearances. The first appearance was in the second episode where Natsu and Lucy tried to find Macao since he disappeared on a mission. They travel to Mt. Hakobe. During that time, the Vulcan that used a Take Over on Macao kidnapped Lucy. After the Vulcan shoves Natsu off the mountain and says, "Don't need men. Only want women." This is evidence that they lust after girls. The Vulcan even went so far as to fight with Lucy's celestial spirit, Taurus, over who she belonged to. While they appear to be stupid lustful apes, they can also be fairly clever. After Taurus is out of commission, the Vulcan picks up the fallen ox's axe and uses it to fight Natsu. This also occurs in chapter three of the manga.
The second appearance is in episode 20, "Natsu and the Dragon Egg". The forest variant of Vulcans, Gorian, goes after what Natsu believes is a dragon egg. Natsu then challenges the Vulcan to a fight while Lisanna tends to the egg. The Vulcan is also very boastful. When Natsu says that he'll beat Gorian with only his fists because the Vulcan is only fighting with his fists, Gorian swats him away like a fly. Then he laughs, "Beat me? How?" They are also easy to irritate. After Natsu pisses him off, Gorian threw a tantrum and that led to his defeat.
In episode 73 (Rainbow of Sakura), Erza, Gray, and Natsu fight multiple white Vulcans similar to the vulcan in the second episode. Natsu wants answers out of the vulcan about the herb they are looking for. Later in the episode, a vulcan is seen spectating the battle between large winged creature (a dragon or gargoyle shape) and Natsu, Gray, and Era.