Last night during the second formicarium challenge the wolf spiders ran into my base and 4 or so of them never actually entered my nest. I didnt notice till everything was dead and there was a few red health bars left right under the holes to the nest on the surface map. I tried to swarm around then and nothing happend. I was actually able to fix it by entering arachnophobia mode. that seem to un-jar them. they died and the level ended.

hope this helps.