True things about roof rats that are genuinely hard to believe, in two flavors: Awwducational (a cute fact with a picture) and Today I Learned (a surprising fact with a source you can check). Every claim links to its source, and the numbered notes at the bottom link straight to the research. A few facts rest on our own colony’s experience and carry an internal source tag, meaning we have not yet found an outside citation that meets Reddit’s sourcing bar for them.
Aww, but true
Rats laugh when they play (and when you tickle them)
Here is a fun one: rats are ticklish. Young rats chirp out a stream of ultrasonic ‘laughter’ at around 50 kHz while they play, and if you tickle one, it laughs the same way and then chases your hand asking for more. Researchers measure it as a real, reward-seeking burst of joy.[1][2] That work was done on lab rats, so whether our roof rats laugh just the same is something I would love to find out.
Source: Tickling induces reward in adolescent rats (Physiology & Behavior (PubMed)) · More: our open question on roof-rat tickling and laughter
Rats will free a trapped friend, just to help
Rats are kinder than people give them credit for. Put a rat next to a cagemate trapped in a little restrainer and, after a few days, it learns to pop the latch and let its friend out, with nothing in it for itself. Offer it a pile of chocolate at the same time and it still frees the trapped rat first, then shares the chocolate.[3] Try to remember that the next time someone calls a rat a pest.
Source: Empathy and pro-social behavior in rats (Science (PubMed)) · More: our open question on roof-rat empathy
Rats replay their day in their sleep, a bit like dreaming
Your rat almost certainly dreams. After it runs a maze and then drifts into REM sleep, its brain replays the very same patterns, in the same order and over the same stretch of time, as when it was awake.[4] So when you catch those little paws twitching in its sleep, it may well be running that maze all over again.
Source: Temporally structured replay of awake hippocampal activity during REM sleep (Neuron (PubMed))
Roof rats are born to climb, and happiest upside-down
The roof rat did not earn its name by accident: it is a tree-dwelling species, built to climb. Ours will scoot along the underside of a wire cage top almost as easily as they walk the floor, then turn around and do it again just for the fun of it. Give them a tall cage with ropes and hammocks and you will see it every day. This one is our own colony’s everyday observation, not something I can point to a study for just yet.
Internal source: What makes roof rats different (Blonde Roof Rat (our own colony)) · More: how climbing shapes the project’s story
Today I learned
Rats physically cannot vomit
Rats physically cannot throw up. They have neither the anatomy nor the brain wiring for it, so a rat can’t vomit up something bad or even burp up trapped gas.[5] That is exactly why a smart rat nibbles just a crumb of anything new first: it can’t undo a bad decision, so it hedges its bets.
Source: Why can’t rodents vomit? A comparative behavioral, anatomical, and physiological study (PLoS ONE (PubMed))
The gene that makes a rat blonde also helps run its lungs, blood, eyes, and kidneys
The single gene behind our blonde roof rats, Rab38, is a busy little thing. The same gene helps build the lung’s surfactant, the clotting granules in blood platelets, the pigment layer of the eye, and the kidney’s protein-recycling machinery (a role in eye pigment is inferred from a related gene, not shown directly).[6][7][8][9] Every piece of that is published on its own, but stitching them into one ‘six jobs from one gene’ story is my synthesis, so I am flagging it as internal until a single paper ties the whole bow.
Internal source: How roof rat coat color works (Blonde Roof Rat (our synthesis of published sources)) · More: the ambroxol page’s Rab38 story
#A rat’s red ‘tears’ are not blood, and a stuffy nose is the real emergency
If you ever see a rusty-red crust around a sick rat’s eyes or nose, it isn’t blood. In Norway rats it is porphyrin, a pigment they leak when stressed or unwell. In a roof rat, watch for CLEAR discharge, not red. “I’ve never seen any roof rat get porphyrin. Their discharge is clear, and if you see it, it is usually a sign of serious infection.” What to watch for instead, in his words: “They don’t have that red discharge that Norway rats have, but sunken eyes and (very bad) runny nose mean the same thing.” (the breeder, from his own account) So on a roof rat you are watching for the wrong thing if you are watching for red at all. (the breeder, from his own account)[10] The thing that should actually worry you is a stuffy nose, because rats can only breathe through their noses, so a blocked one is a genuine emergency.
Source: Basic Information Sheet: Rat (Lafeber Veterinary)
#
Citrus peel oil harms male rats’ kidneys, but not females’
Here is a strange one: the oil in citrus peel (d-limonene) damages the kidneys of male rats only. It binds a protein that only males make, so the females are completely unaffected.[11] That is why citrus is on our do-not-give list: citrus fruits, or fruits with significant amounts of d-limonene (mangos, for example: Google if unsure.) May be OK for female Roof Rats.
Source: Risk assessment of d-limonene: male rat-specific renal tumorigens (PubMed)
Rats re-eat some of their own droppings, on purpose, for vitamins
This one sounds gross but it is not a problem: rats make a special soft dropping and eat it again, on purpose. It is how they get their vitamins B12 and K2, which their gut makes too far down the line to absorb the first time around.[12][13] So don’t scrub the cage spotless and don’t be alarmed, it is just a rat topping up its vitamins.
Source: Coprophagy and vitamin B12 in the rat (PubMed) · More: the glossary note on B12 and coprophagy
Almonds, a treat rats love, can kill them
Almonds look like health food, but they are loaded with oxalate, and a rat that gorges on high-oxalate nuts can go straight into kidney failure.[14][15] We discovered that Kidney disease can be triggered by eating a large amount of almonds in one sitter, which we assume was due to oxalates. A rat here found the almond stash and gorged before anyone could stop him, and was dead of kidney failure a couple of months later. So definitely avoid almonds with their skins on, because the skins are where the oxalate is, and never leave large quantities of treats someplace where the rats may find them and gorge themselves. Treats that are safe in moderation may be harmful in large amounts, and your rats will not restrain themselves.
Source: Diet-induced oxalate nephropathy from excessive nut and seed consumption (PubMed)
A black rat’s coat comes from an ‘always-on’ gene, the mirror of human red hair
The black coat of a wild black rat comes from a change in its pigment receptor, MC1R, that jams it permanently ‘on.’[16][17] That is the exact opposite of what gives people red hair, where the very same receptor is switched off.[18] Same gene, opposite switch, opposite result. Genetics has a sense of humor.
Source: Origin of agouti-melanistic polymorphism in wild black rats inferred from Mc1r (PubMed) · More: the black rat and MC1R
#
Roof rats are more like cats than dogs
The pet rat everyone knows, the Norway rat, is a pack animal that wants a pile of friends. Roof rats are a different animal. In our colony they are territorial and independent, each one acting like the place belongs to him, more cat than dog. It is why you can’t just toss two together and expect them to work it out the way Norway rats do; they often won’t. This is our own colony’s finding, and since it runs against the standard rat literature, I am flagging it as internal until someone documents it properly.
Internal source: Roof rat bonding and behavior (Blonde Roof Rat (our own colony)) · More: the same lesson in Lessons from Failures
Breeding animals to be friendly makes them turn spotty and floppy-eared
Here is a strange package deal. When a famous Russian experiment bred silver foxes for nothing but tameness, the calm ones started showing up with white patches, floppy ears, and curlier tails, none of which anyone was selecting for. Breeding for a gentle temperament seems to drag a whole ‘domestication look’ along with it.[19] It is why our own tamest roof rats so often turn up with a white tail tip.
Source: Early canid domestication: the farm-fox experiment (American Scientist) · More: our own domestication-syndrome hypothesis
#Mushrooms make their own vitamin D in sunlight, just like your skin
Leave mushrooms out in the sun and they do exactly what our skin does: turn UV light into vitamin D. A plain white button mushroom can jump to hundreds of IU after about 15 minutes of midday sun,[20] and rats fed those sun-charged mushrooms actually absorb the vitamin D and build bone with it.[21] A cheap, natural way to round out a rat’s diet.
Source: UV-exposed mushroom vitamin D2 is bioavailable and supports bone growth in rats (PubMed) · More: what roof rats can eat
#Broccoli’s famous cancer-fighting compound is destroyed by cooking, before it even forms
Raw broccoli does not actually contain sulforaphane, the compound everyone praises it for. It gets built on the spot by an enzyme, myrosinase, the moment you chop or chew the plant,[22] and that enzyme is wrecked by heat, so thoroughly cooked broccoli can’t make any.[23] If you want the benefit, for you or your rats, serve it raw or barely steamed.
Source: Myrosinase (which forms sulforaphane) is destroyed by cooking heat (PubMed)
#Rats may have taken the blame for the Black Death unfairly
Everyone ‘knows’ that rats and their fleas spread the Black Death. But when researchers modeled how fast the medieval plague actually moved across Europe, the rats could not keep up.[24] Rat-borne plague spreads in a slow, patchy way, killing waves of rats first, yet the Black Death raced through towns far faster than that. The study argues the real drivers were human parasites, our own body lice and fleas, passing the bacterium from person to person. Seven hundred years later, the rat is still trying to clear its name.
Source: Rats cannot have been intermediate hosts for Yersinia pestis during medieval plague epidemics in Northern Europe (Journal of Archaeological Science) · More: the plague question on the MC1R page
#A mealworm can be turned into a vitamin D pill just by leaving it in the sun
You already know your own skin makes vitamin D in sunlight. It turns out bugs do the same trick. Insects put under UVB light build real vitamin D in their bodies,[25] and a UVB-treated yellow mealworm becomes a standout source of D3, the same form we use.[26] So the humble mealworm, already a favorite rat treat, doubles as a tiny vitamin pill if it has seen a little sunshine first.
Source: Evidence of vitamin D synthesis in insects exposed to UVb light (PubMed) · More: what roof rats can eat
#Believe it or not: roof rats and the law
One Canadian province has been ‘rat-free’ since 1950, and even a tame pet rat is illegal there
Picture a whole province where your pet rat is contraband. Alberta has kept itself essentially rat-free for over 70 years, and the law takes no prisoners: the entire genus Rattus is banned, with no exception for tame, captive-bred, or pet rats. A pet rat found there can be legally seized and destroyed and its owner fined. They even run a 310-RATS hotline so the neighbors can turn you in.
Source: History of rat control in Alberta (Government of Alberta) · More: our Alberta roof rat law page
#The pet roof rat is on the ‘100 worst invasive species’ list, so some countries ban it while its near-twin is a normal pet
Our sweet pet roof rat has a rap sheet: the black rat is one of just 100 animals and plants on the IUCN’s list of the world’s worst invasive species, mostly for the island bird colonies it has raided over the centuries. Because of that label, some countries, like the Philippines, ban keeping one as a pet, even though the nearly identical fancy rat (a different species) is sold freely. The ban is about the list, not the tame little guy in your hands.
Source: 100 of the World’s Worst Invasive Alien Species (IUCN Invasive Species Specialist Group (GISD)) · More: our Philippines roof rat law page
#In Britain you can legally own a roof rat, but releasing one is a crime, even by accident
In Britain you can legally own a roof rat, but letting one loose is a crime, even by accident. The species sits on Schedule 9 of the Wildlife and Countryside Act 1981, which makes releasing it or even letting it escape a strict-liability offence, so intent doesn’t matter. Honestly, that matches our own hard rule anyway: keep them, love them, but never, ever let one out.
Source: Wildlife and Countryside Act 1981, Schedule 9 (legislation.gov.uk) · More: our United Kingdom roof rat law page
#A 2003 monkeypox outbreak is why you still can’t import an African rodent into the US
One bad shipment in 2003, and the rule is still on the books. That year, imported African rodents carried monkeypox into the United States through the pet trade, infecting people who had bought prairie dogs kept nearby. The CDC responded by banning imports of all African rodents, and that ban is still in force today. It is also why a roof rat coming from an African country gets turned away at the Canadian border.
Source: Bringing an Animal into the U.S. (African rodent import ban) (U.S. Centers for Disease Control and Prevention)
#In Switzerland it is illegal to keep just one rat!
Swiss animal-welfare law treats rats, along with guinea pigs, mice, and other “social species,” as animals that suffer when kept alone, so you are required to keep at least two. The same rules that protect the fancy rat cover the roof rat. It is, in effect, illegal to let a social animal be lonely. Which means that if someone had a territorial male roof rat, Switzerland would legally require the owner to place another roof rat in the same cage with him, even if that resulted in injury or death of their pets. Possibly this rule was created by the same folks who also legally require you to shake hands with everyone when you walk into a room? LOL! So while you can legally keep roof rats in Switzerland as pets, make sure you get bonded males or females, and hope they never start fighting, later.
Internal source: our roof rats are territorial, which is what makes this a catch-22 (Blonde Roof Rat (our own colony finding))
#In a couple of places, the only pet rat the law allows is a white one
In Alaska and in the city of Denver, whether a pet rat is legal can come down to the color of its coat. Both use a ‘clean list’: you may keep only an animal written onto the list by name, and everything else is barred. The one rat on Alaska’s list is the albino lab rat, the pink-eyed white one, and a roof rat of any color is not on it. Denver goes further and names a color outright, permitting only the ‘Domestic laboratory rat (Rattus rattus albino strain).’ So in Denver a snowy-white roof rat can be a legal pet while its agouti littermate, same species, same cage, is contraband a block away.
Source: 5 AAC 92.029 (Alaska clean list: only ‘White rat Rattus norvegicus Var. albinus’); Denver R.M.C. 8-72(b)(7)(j) (‘Domestic laboratory rat (Rattus rattus albino strain)’) (Alaska Board of Game / City and County of Denver) · More: our Alaska roof rat law page
#References
- [1] Burgdorf J, Panksepp J. “Tickling induces reward in adolescent rats.” Physiology & behavior 2001;72(1-2):167-73. PubMed.
- [2] LaFollette MR, O’Haire ME, Cloutier S, et al. “Rat tickling: A systematic review of applications, outcomes, and moderators.” PLoS One 2017;12(4):e0175320. PubMed.
- [3] Ben-Ami Bartal I, Decety J, Mason P. “Empathy and pro-social behavior in rats.” Science 2011;334(6061):1427-1430. PubMed.
- [4] Louie K, Wilson MA. “Temporally structured replay of awake hippocampal ensemble activity during rapid eye movement sleep.” Neuron 2001;29(1):145-156. PubMed.
- [5] Horn CC, Kimball BA, Wang H, et al. “Why can’t rodents vomit? A comparative behavioral, anatomical, and physiological study.” PLoS One 2013;8(4):e60537. PubMed.
- [6] Zhang L et al. “Rab38 targets to lamellar bodies and normalizes their sizes in lung alveolar type II epithelial cells.” American Journal of Physiology. Lung Cellular and Molecular Physiology 2011;301:L461-L477. PubMed.
- [7] Ninkovic I et al. “The role of Rab38 in platelet dense granule defects.” Journal of Thrombosis and Haemostasis 2008;6(12):2143-2151. PubMed.
- [8] Loftus SK et al. “Mutation of melanosome protein RAB38 in chocolate mice.” Proceedings of the National Academy of Sciences 2002;99(7):4471-4476. PubMed.
- [9] Rangel-Filho A et al. “Rab38 modulates proteinuria in model of hypertension-associated renal disease.” Journal of the American Society of Nephrology 2013;24(2):283-292. PubMed.
- [10] LafeberVet. “Basic Information Sheet: Rat.” link.
- [11] Hard GC et al. “Risk assessment of d-limonene: an example of male rat-specific renal tumorigens.” Critical Reviews in Toxicology 1994. PubMed.
- [12] Morgan TB, Gregory ME, Kon SK, Porter JW. “Coprophagy and vitamin B12 in the rat.” British Journal of Nutrition 1964;18:595-602. PubMed.
- [13] Groenen-van Dooren MM et al. “Bioavailability of phylloquinone and menaquinones after oral and colorectal administration in vitamin K-deficient rats.” Biochemical Pharmacology 1995;50(6):797-801. PubMed.
- [14] Garland V, Herlitz L, Regunathan-Shenk R. “Diet-induced oxalate nephropathy from excessive nut and seed consumption.” BMJ Case Reports 2020;13(11). PubMed.
- [15] Pal A, Aydin-Ghormoz E, Lightle A, et al. “Diet-induced hyperoxaluria: a case based mini-review.” Clinical Nephrology Case Studies 2024;12:52-57. PubMed.
- [16] Kambe Y et al. “Origin of agouti-melanistic polymorphism in wild black rats (Rattus rattus) inferred from Mc1r gene sequences.” Zoological Science 2011;28:560-567. PubMed.
- [17] Benned-Jensen T, Mokrosinski J, Rosenkilde MM. “The E92K melanocortin 1 receptor mutant induces cAMP production and arrestin recruitment but not ERK activity indicating biased constitutive signaling.” PLoS ONE 2011;6(9):e24644. PubMed.
- [18] Mogil JS, Wilson SG, Chesler EJ, et al. “The melanocortin-1 receptor gene mediates female-specific mechanisms of analgesia in mice and humans.” Proceedings of the National Academy of Sciences 2003;100(8):4867-4872. PubMed.
- [19] Trut L. “Early Canid Domestication: The Farm-Fox Experiment.” American Scientist 1999;87(2):160. DOI.
- [20] Urbain P, Jakobsen J. “Dose-response effect of sunlight on vitamin D2 production in Agaricus bisporus mushrooms.” Journal of Agricultural and Food Chemistry 2015;63:8156-8161. DOI.
- [21] Calvo MS, Babu US, Garthoff LH, Woods TO, Dreher M, Hill G, Nagaraja S. “Vitamin D2 from light-exposed edible mushrooms is safe, bioavailable and effectively supports bone growth in rats.” Osteoporosis International 2013;24:197-207. PubMed.
- [22] Zhang Y et al. “A major inducer of anticarcinogenic protective enzymes from broccoli: isolation and elucidation of structure.” Proceedings of the National Academy of Sciences 1992;89(6):2399-2403. PubMed.
- [23] Okunade OA et al. “Thermal and pressure stability of myrosinase enzymes from black mustard (Brassica nigra L. W.D.J. Koch. var. nigra), brown mustard (Brassica juncea L. Czern. var. juncea) and yellow mustard (Sinapsis alba L. subsp. maire) seeds.” Food Chemistry 2015;187:485-490. PubMed.
- [24] Hufthammer AK, Walløe L. “Rats cannot have been intermediate hosts for Yersinia pestis during medieval plague epidemics in Northern Europe.” Journal of Archaeological Science 2013;40(4):1752-1759. DOI.
- [25] Oonincx DGAB et al. “Evidence of vitamin D synthesis in insects exposed to UVb light.” Scientific Reports 2018;8:10807. PubMed.
- [26] Nölle N, Hörnstein A, Lambert C. “Vitamin D fortification of selected edible insect species through UVB-treatment.” Food Chemistry 2024;444:138679. PubMed.