I first discussed this on Yog Radio; those wanting the audio can listen to that here.
Richard Marsh is one of those unlucky authors who seem to vanish from the scene through no fault of their own. Here he's created an Orientalist Victorian melodrama on a par with Dracula, which was published in the same year. Initially The Beetle was more popular than Stoker's bloodsucker, yet it's Stoker that gets remembered while Marsh languishes in obscurity.
I don't think that can be blamed on quality of output. Marsh and Stoker were equally prolific, more or less, and neither of them seem to have been successful with anything other than their 'name' works. Yes, Stoker's Lair of the White Worm and Jewel of the Seven Stars occasionally turns up in print, but I doubt that anyone reads those for fun. They're the sort of thing that a hard-core Stoker fan will devour just to say they've done it, but nobody else can stomach.
I also don't think Vampires can be blamed for this. Yes, Stoker kicked off the bloodsucker industry, with all the shlock that goes with it. Yet before Stoker there wasn't a vampire market; they turn up now and again, in Byron's (Polidori's?) poetry and Wuthering Heights, but to me that seems less an unstoppable tide and more a slight splash. Vampires, as we've come to know them, weren't inevitable.
No, I think Bela Lugosi's got a lot to answer for.
Well, him and Hollywood. The very first was, of course, Nosferatu, which wasn't a Dracula movie, honest luv, now stop trying to set fire to the film reels there's a good gel. That was just a teaser: the main event came in 1931, when Universal suddenly realized there was good money to be made in horror. Then followed a host of other shockers, some of which caught the audience's imagination, while others quietly died. Universal was willing to raid almost any crypt for inspiration, and it's not as though they were the only movie studio who saw the potential in chills. Film kicked the vampire up from the minors to the majors. So why was there no Beetle, to go with those invisible men and lupine horrors?
Well, there's the rub. It could have been The Beetle, but for one thing: it's not a cinematic property. Anyone who reads fantastic literature knows the problem. There are some stories that practically glow with genius, but when it comes to the big screen, they die on their feet. Moving pictures, by definition, move; there has to be action, and if most of the fun stuff is happening in the character's head, translating that to the silver screen will be a thankless task. Psychological portraits are extremely difficult to do, and the Beetle is one of those thorny subjects in which, bar one train crash, there isn't much action. Plenty of chills and gothic horror galore, but no screen shocks to go with it.
Yet it could be done, and perhaps will be done, one day. I can but hope!