Must admit, last night it had it's eye on a rather docile but still buzzing fly on a window that she couldn't reach, so I created a ladder for her to get up to it, and watched her kill and eat it over the space of about 15 minutes.
Our spider and fly situation has really improved since we got them.
" the little one doesn't seem to be eating much yet. ....quite handy at catching flies"
you answered your own question ;-)