H. gigas is OW and does not have urticating hairs. OW species still can get bald spots though for a variety of reasons, (stress from shipping, etc.) Most t's look pretty ragged prior to a molt. I wouldn't worry about it as long as it is acting normally. The bald spot will disappear with the next molt. Of course, by then, you probably won't be seeing much but a hole in the substrate and an occasional leg sticking out of it.