Although sometimes called "collectors," a benign term equating them to collectors of baseball cards or teacups, a more accurate term is "animal hoarder." It is now considered to be a distinct mental disorder. It is most often characterized by an individual amassing a large number of pets, failing to provide them with proper food, water, shelter, veterinary care, and sanitation, resulting in squalid living conditions for both the animals and the hoarder. The hoarder also fails to act on the animals’ deteriorating condition, which often includes severe starvation, dehydration, parasite infestation, rampant disease, attacks among animals, cannibalization, and uncontrolled breeding, making the situation even worse over time. Sanitary conditions often deteriorate to the point where living and food preparation areas no longer server their original purpose, as clutter, urine and feces accumulate in living spaces.

At Tufts University in Boston, a group call the Hoarding of Animals Research Consortium (HARC) is studying the many cases of animal hoarding reported each year. The group consists of professionals in psychology, sociology, veterinary medicine, and animal protection. Their goal is to work collaboratively in hoarding cases to achieve a more humane and lasting intervention. Because hoarding has only recently been recognized as a clinical condition, there is no single protocol for treatment as yet.

The majority of hoarders are women and the most commonly hoarded animals are cats. Some, as we see in the examples above, are couples. Nearly all hoarders are self-proclaimed animal lovers and believe they are rescuing the animals from some terrible fate.