they look like aliens
they are ancient
they live on land
they might be living in your next door forest, in fact
under your very nose, or shoe
(scary music here)
The slime molds.
Their real name is "Physarum polycephalum" which, as you know only too well, means "many-headed slime mold"
which, aside from anything else, provides us with a fabulous name to call someone you don't like.