Critter and Bug Smells simply adds smells to all critters and bugs to help creatures find them easier. More specifically, it gives critters and bugs CA 0. There's also a few tweaks to let CA 0 travel like other CAs. Otherwise it wouldn't travel properly. Since it uses CA 0, and only CA 0, it doesn't conflict with agents that use CA 19, like the New Toy Smell. It also has an auto-recovery script heavily inspired by the one from Snap out of it. So any unknown bugs don't stop critters and bugs from smelling.
If you're upgrading from version 1, either start a new world or remove the old version of the agent before installing the new one. I'd recommend starting a new world but that's mostly because I don't know if CACL can connect more then one agent type to a smell. If so, you might have some very confused norns if they look for a critter/bug and find a toy instead.
Here's a Creatures Caves download and an alternative download.