It’s also smart to make use of your Igni sign (they’re weak to fire), coat your weapon with Insectoid Oil and attempt to attack the beasts from either the sides or the back to increase damage. It’s best to rely entirely on heavy sword strikes when going against an Endrega as they easily shrug off the faster attacks.
You have four varieties with these things: the smaller, regular Endregas, the harder-hitting warriors (increased damage and can knock you over with rushing attacks), the still harder-hitting guards and the monstrous queen Endrega. Much more dangerous than Nekkers, these heavily armored insectoids can take Geralt down with just a few good hits.
An Endrega is like a spider crossed with a silverfish that grew impossibly large off of a diet of human babies and your worst nightmares.