That always bothered me. Reapers converted harvesters, but why not klixen? Imagine that terrifying skull face amplified with reaper tech. Yeah, I'd be about as terrified as when I viewed full banshee anatomy.
True story: My memory went hazy and I threw "klixen" into Google's image search (uncensored results as always) without adding "Mass Effect"...and then I had a good laugh before correcting the mistake.