Yesterday, when I went out to mail something, I found a couple pretty tall sand mounds on either side of one of my front walkway cement blocks. They looked like ants had built high rise hotels over night as I didn't recall seeing them the previous day.
So, I tried the trick of dumping boiling water on the mounts to get the ants to move (and kill some along the way as any colony making them that big, that fast, had to be a lot). So I washed both away and planned to see if they came back.
Much to my surprise, within a couple hours, the mounds were almost back. I'd never seen ants build a mount that fast. So then I decided to go for the bug killer spray. I dumped some over one mound. Then as I started dumping onto the other mound - much to my surprise, a giant female bumblebee emerged from the far side of the sand!
I quickly backed away into the house as the bumble flew off over the front yard.
I know bumblebees are mostly docile, and it was the only one that emerged, so I think it was a young female looking for a place to hibernate in a couple months. I hope I didn't accidentally kill it with the insecticide, but there's no way she's taking up residence under my front sidewalk - way too dangerous for anyone coming to my door - and me, as I have an allergy to bee stings.
I'll keep monitoring to see if she comes back or if she was scared away (hopefully not dead!). If she comes back, I'll try watering her out by using my hose to make the space not livable so she finds someplace else with less human traffic. Must admit - that was a first.
I've seen bumblebees flying around the house, just never burrowing under a sidewalk. I had a nest/hive in my backyard this summer in some thatch I dumped back there, I left it alone as they helped pollinate my garden and it was in the corner of the lot - easy to avoid.
Was amazed at how fast that thing built its home in the sidewalk cracks - never seen anything like it.