In Fantastic Beasts And Where To Find Them, after arriving in New York City (and I think only after his collection of magical creatures escapes his suitcase), Newt Scamander notices a bright blue insect that looks a bit like a wasp, several times. What is this thing, and does it have any significance in the plot? Is it a local creature that he longs to capture and study, or something he had inadvertently brought with him?
It's apparently a beetle called a Billywig. This Insider piece describes it. Here is an extract from there:
The sapphire blue insect has a stinger and wings on its head that let it spin while it flies. People stung by Billywigs may levitate while having a mild case of giddiness.
I don't recall seeing it come out of the Newt's case, but I am thinking it is not local to NYC because people don't seem to be levitating there for no apparent reason. I think Newt longs to closely study all magical creatures, so I would think the billywig is included.
It's a Billywig. He brought it with him and it escaped from his case. Strangely, they never show him recapturing it, or explain what happened to it. http://harrypotter.wikia.com/wiki/Billywig