What does the word "tiddlers" mean as used below?

" "Although we do not yet have the
capability to detect 'tiddlers' like the Earth, we
can establish theoretically which of the
exoplanetary systems are most likely to have an
'Earth'," said Professor Barrie Jones of The
Open University. "

Edit: I found this, in a site about a Dylan Thomas work. Does then "tiddlers" mean Earth
is a "little fish" as planets go?