I've used this brand of rat bait off and on for years.  In the past, the rats eat it and then they die (I know because I find them.)  This time, though, either they're taking these little blocks and building a "Rats of NIMH" castle, instead of eating it, or it's just not as potent as the old Tomcat baits I've used in the past.  I suppose, it might be working, and there are just hundreds of rats in this colony!  The baits disappear, but the next day, the rats are back in the bird feeders just like the day before.

Update.  Over two months of use now, and the nine pounds of bait is almost gone, but I can detect no reduction in rat activity.  I've recently learned that the active ingredient in this product, diphacinone, is one of the products known as first generation rodenticides, along with warfarin, pindone, and chlorophacinone.  Rats have been found in some cases to become resistant to these products.  In such cases, a 2nd gen product is needed.  Brodifacoum and Bromadiolone are two such products.  Of course, there are other reasons why this bait could be failing to do the job.  Here is a link to a U.C. Davis article: [...]  The article addresses several reasons for bait failure, and I'll address them all, including moving to another bait when I've used up the last of the Tomcat.

It's now October, so I've got to get rid of these things before the weather turns colder and they decide to move inside!
I've used this brand of rat bait off and on for years. In the past, the rats eat it and then they die (I know because I find them. )  This time, though, either they're taking these little blocks and building a "Rats of NIMH" castle, instead of eating it, or it's just not as potent as the old Tomcat baits I've used in the past. I suppose, it might be working, and there are just hundreds of rats in this colony! The baits disappear, but the next day, the rats are back in the bird feeders just like the day before. Update. Over two months of use now, and the nine pounds of bait is almost gone, but I can detect no reduction in rat activity. I've recently learned that the active ingredient in this product, diphacinone, is one of the products known as first generation rodenticides, along with warfarin, pindone, and chlorophacinone. Rats have been found in some cases to become resistant to these products. In such cases, a 2nd gen product is needed. Brodifacoum and Bromadiolone are two such products. Of course, there are other reasons why this bait could be failing to do the job. Here is a link to a U. C. Davis article: [... ]  The article addresses several reasons for bait failure, and I'll address them all, including moving to another bait when I've used up the last of the Tomcat. It's now October, so I've got to get rid of these things before the weather turns colder and they decide to move inside!