When attacked, they create an electric barrier by spitting out many electrically charged threads.
(From Bulbapedia)Galvantula's body consists of a head and abdomen. Its head is yellow on top and light purple on the bottom. It has two large, blue, forward-facing eyes with black pupils, and four, smaller, simple eyes sitting in a 2x2 pattern on its forehead. It has two long pedipalps connected from the underside of its head, which are blue and hairless on their lower half and covered in thick yellow fur on the upper half. Galvantula's body is covered in yellow and light purple fur on top with blue fur under its abdomen. Four tufts of hair sprout from under its abdomen and grow upward. Two large tufts sprout from the left and right of the rear, while two smaller ones sprout from each side. The fur on its back is light purple and with three thick, yellow stripes running up from its rear. Despite being based on a spider, Galvantula has only four legs. Each leg is connected to the head by a blue upper half. The lower half is covered in yellow fur and forms a bell-shape over its blue, conical feet.
Galvantula, and its pre-evolution Joltik, are the only Pokémon that can learn Electroweb by leveling up. Galvantula in particular likes to use electrically charged silk to ensnare prey. The electricity stuns the victim, allowing Galvantula to consume the target at its leisure. Its pedipalps are very strong, allowing Galvantula to hold down unruly prey. It also uses electric webs to defend itself from threats. As seen in the anime, Galvantula is not particularly aggressive unless provoked. If bothered, it may attack in groups. It has been shown to be extremely caring and protective of its pre-evolution, Joltik, and will aggressively find ways to help it.