Muggles' Guide to Harry Potter/Magic/Skrewt

Overview
Blast-Ended Skrewts are creatures that look like deformed, shell-less lobsters, with no visible head, that periodically boost themselves forwards with an explosion in their tail.

Extended Description
Hagrid has somehow secured several hundred of these creatures just after they hatch, and proposes to have Harry's class look after them as they grow. And they do grow through the course of the book, developing shells and bad tempers, though it seems that we never discover what exactly they eat, apart possibly from each other – though we started the year in early September with several hundred, by the end of October they have started killing each other (by Hallowe'en there are only twenty left, in individual boxes), and only three grow to maturity. Of these three, at least one is in the Third Task maze, where it is reportedly over six feet long. One of them evidently does not survive its time in the maze, as later Hagrid asks the Trio if they want to visit the two remaining Skrewts.

The Skrewts come in two varieties: one with an apparent stinger, which Hagrid presumes is male, and one with suckers which might be for sucking blood, which is presumed female.

They have caused many injuries to the students who look after them.

Rita Skeeter describes the Skrewts as "highly dangerous crosses between manticores and fire crabs."

Analysis
It is difficult to say exactly what the purpose of Blast-Ended Skrewts is in our story. Largely they seem to be used to highlight the character differences between the Trio, who assist Hagrid in caring for these creatures even as they grow and become more dangerous, and the rest of the class, who cower in Hagrid's hut while Hagrid and the Trio round up escaped Skrewts. They are also used to show Hagrid's continuing child-like enthusiasm for the more dangerous of magical creatures. They provide some insight into the sorts of effort required to determine the characteristics of newly-discovered or newly-created magical species. On a smaller scale, they provide a hook which Rita Skeeter can use to schedule an interview with Hagrid, and also a dangerous creature for Harry to face in the Third Task maze. Of all of these, it seems that the illumination of character is the only one that can be considered useful to our story; Rita could have hung her interview request on pretty much anything Hagrid chose to do, and there were already large numbers of dangerous creatures available to the Tournament organizers.

Questions

 * 1) Did Blast-Ended Skrewts actually exist as a species, or were they the result of cross-breeding by Hagrid alone (as Rita Skeeter seems to imply)?