Wormhole Threshers are particularly dangerous Threshers, whose main form of attacking is to suck in players, then protrude spikes from their body, dealing constant damage until they die.
Whenever you see a Wormhole Thresher (easily noticeable by their dark color and large white spikes), it is important to focus on them first. Not only can they deal serious damage but their suction ability can be a little disorienting and make fighting more difficult. Further, if your battle begins to go poorly, you likely won't be able to escape until the Wormhole Thresher has been dealt with.