In the Doctor Who episode "School Reunion", the Doctor explains what the Krillitanes are:
They're a composite race. Just like your culture is a mixture of traditions from all sorts of countries, people you've invaded or have been invaded by. You've got bits of Viking, bits of France, bits of whatever. The Krillitanes are the same. An amalgam of the races they've conquered. But they take physical aspects as well. They cherry pick the best bits from the people they destroy. That's why I didn't recognise them. The last time I saw Krillitanes, they looked just like us except they had really long necks.
(For reference, at this point, this Krillitanes are rather large and bat-like.)
I'm somewhat confused by the last line. As far as I can tell, the Krillitanes have not taken over humans in any substantial quantities (besides eating a few) - and those deaths appear to have happened after the Krillitanes arrived in their bat-like form.
Why did the Krillitanes look like humans? Does the Doctor just mean that they looked like humans relative to their current form, or is he saying that the looked almost exactly like humans?