Tend the Pests is a spell that makes you sacrifice a creature you control in order to create X amount of pests where X is equal to that creature’s power.
Since it is a spell it triggers Dack Fayden’s Magecraft ability that lets you take control of an opposing creature until end of turn.
However, if there are no opposing creatures to take control (which causes Dack’s Magecraft prompt to never trigger) Tend the Pests doesn’t creates any pest tokens after you sacrifice your creature. As seen on this video:
If the opponent has creatures for you to take control but you chose not to do it, once again Tend the Pests will not create any pest tokens after you sacrifice your creature. As seen on this other video:
You need to wait until your opponent has creatures in play and chose to steal them when Dack’s Magecraft ability trigger in order for Tend the Pests to create any pest tokens after you sacrifice your creature. As seen on this last video:
All those videos were recorded during the same game so nothing changed besides what I decided to do with when Dack’s prompt triggered