Black spot on my front walk.....

[moose35]

what could it be...

hmmm...maybe we need a closer look

it looks like its moving.

yep ants....

moose

 

[chebe2]

Ants!!!!!

Down here in louisiana they do this all the time when it rains for a few days!

 

[H. laoticus]

wow, impressive gathering of ants!

What causes them to do that? Evacuation?