Why do you need the white witch's DNA for?
Alex - DNA tells you a lot about how closely related one organism is to another. One example: when I thought I had discovered a new species of wasp, I couldn't really be sure if it was really different from its closest relatives. It looked a little different, but so do, for example, a beagle and a pit bull, even though they are the same species. So appearances can fool you.
But not DNA - we found that there were differences at the level of genes, a kind of proof that we had 2 species.
In the case of the white witch: If we had some moths collected from French Guiana, and some others from Mexico, the DNA could tell us it these were 2 different populations. If they are, then we know that moths from each population come from different places (an alternative hypothesis is that all white witches come from just one place).
But when we extracted DNA from samples of the wasps, we saw that we had 2 kinds of evidence. One