Eeeek! Bugs in my seeds!

Someone please tell me what's going on... I harvested my hardy pink hibiscus seeds a couple of weeks ago, made sure they were dried out enough, then put them in a brown coin envelope. I have a basket with alphabetized index cards and stuck them in there for a couple more weeks. This morning I went to collect a few of my seed envelopes for trades and brought them into our home office and set them on the desk. I did a few other things, but kept hearing a strange noise coming from the desk area and about 3 hours later curiosity got the best of me and started to investigate. I looked all over my desk and realized the noise was coming from those envelopes. I picked them up one by one, shook them, and suddenly when I picked up the hibiscus seed envelope I saw some tiny black insects crawling all over it. I opened up the envie and it was filled with these bugs, some of which flew away. They're almost as small as knats, but darker and heavier. I took the envie outside and dumped it into a plastic container, shook it around and watched as all those bugs scrambled about with some flying away. There were hundreds of them. I noticed most of my seeds had tiny holes in them, too. Did the bugs come out of the seeds, or were they burrowing into the seeds? What in the world are they anyway?

JoAnn