According to Wikipedia:
A pack rat or packrat, aslo called a woodrat, can by any of the species in the rodent genus Neotoma. Pact rats have a rat-like appearance with long tails, large ears and large black eyes. Compared to deer mice, harvest mice, and grasshopper mice, pack rats are noticeably larger and are usually somewhat larger than cotton rats.
Each species of pack rat is generally restricted to a given type of habitat within its range. Pack rats live anywhere from low, hot, dry deserts to cold, rocky slopes above timberline. Pack rats build complex houses or dens made of twigs, cactus joints, and other materials. These contain several nest chambers, food caches, and debris piles. Dens are often built in small caves or rocky crevices, but when close by human habitations, woodrats will opportunistically move into the attics and walls of houses.
Bushy-tailed woodrats feed primarily on green vegetation, twigs, and shoots. Mexican pack rats eat seeds, fruits, acorns, and cactus.
Adult bushy-tailed woodrat males usually weigh 300-600 g with an average of 405 g, and adult females usually weigh 250-350 g with an average of 270 g. These ranges are relatively large because this species occupies a large geographic range, and its body size is closely correlated with climate. Average males range in size from 310-470 mm with the average being 379 mm and average females range fro 272-410 mm with the average being 356 mm.
Reproductive habits or rodents are variable in the wild and can become more so when domesticated. Most are born naked and helpless and must be cared for in nests. Some female pack rats have been known to deliver up to five litters per year with each litter having as many as five young. The offspring may open their eyes between 19-12 days after being born and are usually weaned between 14 and 42 days. After around 60 days, most become sexually active.
* Please note . . . Pets are not allowed.