Roof Rat (Black Rat)
- The roof rat (black rat) is the species of rat that carried bubonic plague-infected fleas, whose spread between 14th and 18th centuries killed almost 75 million people worldwide.
- The number of human lives taken by rat-borne disease is believed to be greater than the deaths caused by all wars combined.
- In its habitat, the black rat loves to climb and dwell in trees, especially pines and palm trees, where he builds nests out of sticks and leaves.
- The house rat is a highly adaptable creature that can survive in almost any kind of situation: being without water, falling from great heights, being exposed to radiation, and even ingesting some poisons.
- The roof rat has recently outranked the Norway rat as the most common species of rat living close to people, being particularly fond of high-moisture areas such as canals and sewers.
The roof rat (black( is a medium-sized rat with an average head-body length of 14-22 cm, a tail of 19 cm or longer (sometimes up to 28 cm), and a body weight between 75 g and 230g. It has relatively long ears, a pointed muzzle (the nasal bones are relatively narrow), and a body more slender than the brown rat. Its naked tail is almost always longer than its body, with over 200 rings. The fur is glossy, but not very dense, varying in color from grey to brown and black with a white ventral belly. The male’s body is larger than the female’s. Compared with the brown rat, the house rat has a lighter skull and finer fur.
Diet, Behavior & Habits
Although roof rats are omnivorous, their diet consists mostly of fruit, grains, and nuts (similar to that of tree squirrels). They also feed on other vegetation (including ornamental and native plants) and occasionally on invertebrates and small vertebrates or carrion. Their daily intake averages 15 g of food and 15 ml of water. Although their diet differs greatly from that of Norway rats, they will feed on almost anything if necessary. They are also big fans of animal feed and pet food. In the wild, black rats love fresh and dry fruit, seeds of all kinds, tree bark, and various plants, but they will not say no to insects, slugs, snails, and birds’ eggs. Excess food is stored at a certain distance from their nest.
Black rats are nocturnal creatures by nature, especially in the wild, but they are often active at all times when dwelling in dark corners of barns and warehouses. They build nests for their young using sticks and leaves, but it is not uncommon to dig burrows, as well. They are avid climbers, which allows them to build their homes in attics, roofs, and in arboreal habitats. Although they aren’t truly social in nature, black rats are rarely seen alone, often living in small, organized groups consisting of a dominant male and several males and females with their young. Dominant males have greater access to females and mate more often than subordinate males. They are very territorial and aggressive – although females have been reported to be more aggressive than males - and they will defend the integrity of their nest at any price.
breeds all year long if conditions are favorable, although summer and autumn are the most productive periods. They can produce up to 5 litters per year, each with 6 to 12 offspring, which have a gestation period of 21-29 days. One month after birth, rats no longer depend on others for feeding and protection; after 3 to 5 months, they become sexually active. Males contribute the least to the care of the young, which remain relatively helpless for the first couple of weeks of their lives when they eyes open, their fur begins to grow, and they are finally able to start foraging. They remain in the nest until they reach adulthood.
Their vision is not great (they are considered color-blind and able to distinguish only lightness from darkness), but they rely on their excellent senses of smell, taste, and touch to locate food sources, establish travel routes, and recognize other rats. They use their whiskers and hairs on their body as tactile sensors, enabling them to figure out travel routes and guide them through dark. They also have an excellent sense of balance, moving much faster and being more agile than Norway rats.
Signs of Infestation
There is often more difficult to recognize a roof rat infestation compared to a Norway rat infestation since the first may often live on superior floors, in attics, on the roof, above ceilings, or in crawlspaces, out of which they only venture to get food and water. As a result, it may be useless to inspect for droppings, urine, and tracks in order to diagnose an infestation. Smudge marks (the oil marks left by their bodies as they rub their fur off walls whenever traveling along aerial routes) may be encountered in food-processing and storage facilities.
On residential properties, black rats may:
- Tear up insulation
- Destroy electrical wiring
- Feed on and contaminate stored food
- Disable freezing units and refrigerators by gnawing on wiring
- Feed on and destroy ornamental plants and other vegetation
In certain agriculture areas, roof rats may:
- Cause considerable losses of tree crops (citrus, avocados, walnuts, almonds)
- Eat orange fruit while still standing on the branch
- Tear down the bark on some small trees and branches
- Feed on and destroy sugarcane crops
- Feed on newly-planted seed of plants, destroying future crops
- Cause certain damage to melon, berry, and vegetable crops when found in the proximity of already infested areas
Management & Control
There are no significant differences between management and control methods for roof rats and Norway rats. A successful control black rat strategy includes sanitation, rodent proofing, and population control.
Sanitation measures should be carried out regularly, otherwise progress obtained will be lost and rats will be quick to return. First of all, good housekeeping is a must, starting from reducing clutter to organizing gardening equipment and cleaning out garbage and debris regularly. If pets are fed outdoors, food bowls should not be left out all day long. The aim here is to reduce or eliminate all food and water sources
Roof rats have excellent climbing abilities, so trimming or thinning vegetation will make their quest of reaching superior floors of the house less easy. Poison ivy, honeysuckle, and other climbing vegetation should be kept within a safe distance from overhanging tree limbs. The same goes for vines and dense shrubbery, which make the ideal hiding place for rodents. In tree crops, it is essential to implement some cultural practices. First of all, remove pre-harvest fruit and nuts on the ground. Secondly, remove vegetation adjacent to crops that could provide shelter for rodents. Also look for nests built on branches or in burrows and remove them immediately.
. Rodent-proofing a building is often considered the most effective method of rat control and can be achieved through the following strategies:
- Seal all cracks and holes between and around plumbing and wiring that could ensure rats’ access through walls and the foundation
- Repair damaged ventilation screens around the foundation; also, check the integrity of indoor ventilation screens on roof and in attic
- Replace damaged screens under eaves
- Make sure all windows and doors have screen doors in good condition
- Use a spark arrester to cover all chimneys
- Ensure that all doors leading outside are weatherproofed and tight-fit
Poison baits, especially the anticoagulant bromadiolone- and brodifacoum-based varieties, are an excellent rodent control method when used in conjunction with trapping. They are slow-acting and may require baiting for several times before eliminating all living rats. Once ingested, the poison causes rats’ blood to lose its ability to clot, soon leading to severe internal bleeding and death. First symptoms are visible after a few days in order to ensure that the rodent will keep on eating it.
For trapping rats and mice in and around homes, trapping is definitely the method of choice, as it is less expensive, less labor-intensive, and generally safer than rodenticides. Snap or glue traps can be set and placed strategically in certain areas frequented by rats such as attics, basements, crawlspaces, etc. Effective baits include peanut butter, fruit, or nutmeats. However, don’t expect them to fall for it as soon as you place it near their nest – being afraid of change, rats will take their time to investigate new apparitions into their environment. Oftentimes, it is the positioning of traps that is the key factor in controlling rodents around the house. For roof rats, ideal locations include fences, pipes, ledges, shelves, and other aerial routes used by rats to come down from their nests and look for food.
Rats are very sensitive to changes in their environment, and even the most minor ones have the potential to make your property less attractive to these pesky creatures. Here are some useful tips:
- Use rodent-proof containers to secure trash and garbage
- Pick up fallen fruit immediately (especially citrus and nuts)
- Remove any attractants and water/food sources (don’t forget about bird feeders and pooling water around your yard)
- Store lumber and other materials away from the ground and walls
- Prune shrubbery so that the ground below them is clearly visible
- Remove dead fronds and aerial pathways provided by vines and branches, and fences
- Remove tree branches that overhang roofs
- Trim or completely remove plants that grow taller than one foot