These tiny (roughly 3mm or less) arachnids are clustered on some slime mould (Fuligo septica). Their name comes from their superficial resemblance to true scorpions, but note that they have no tail. They are also entirely harmless to humans and, in fact, help by preying on ants, booklice, moth larvae, etc.

Both Barry and Isabelle noticed these arachnids and pointed them out to others. Although these creatures are very common, they are not usually noticed until they sit on something like this slime mould which makes them stand out more. On the leaf pile they blend right in. The slime mould, often called dog's vomit (which it does resemble when fresh!), is very common and has appeared on any leaf pile at the garden over the years. In the woods around Ottawa I most often see it on logs and stumps.