We have received several ensign wasp submissions lately. These small wasps are in the Order Hymenoptera (bees and wasps) and Family Evaniidae. Submitters will always note that they are seeing these wasps in the house and want to know if they are dangerous. The good news is that they are not dangerous unless you are a cockroach. Yes, these wasps indicate the presence of cockroaches in the house, usually American, smoky brown or oriental cockroaches. The wasps lay their own eggs in cockroach egg cases and the developing larvae consume the roach eggs. This is biological control in action. The presence of several ensign wasps usually indicates a significant cockroach problem and roach control measures should be undertaken.
Here is the Wikipedia page for ensign wasps. Here is our publication on Recognition and Control of Cockroaches by Wizzie Brown, Mike Merchant and Roger E. Gold.