Armoured Rat

Nov 25

Hoplomys gymnurus

The armoured rat is covered in sharp spines that can grow as long as 3 cm (1.2 in) — a great defence against the snakes and ocelots that share its wet rainforest habitat. Additionally, if all else fails, this rat can drop its tail to confuse or distract a predator.

Armoured and Quilled

Mammals are often considered the softest and cuddliest of all animals. Birds are covered in rigid feathers, reptiles and fish in firm scales, amphibians are slick and slimy, and insects brandish hard exoskeletons. Meanwhile, a mammal has only a layer of squishy skin covered by a fluffy coat of fur or hair. However, there are armoured exceptions — mammals you probably wouldn't want to cuddle.

A nine-banded armadillo (*Dasypus novemcinctus*) on the left and a giant pangolin (*Smutsia gigantea*) on the right.

These can be roughly divided into two groups; the purely defensive tanks and the painful pincushions. The former group includes mammals that enclose their soft bodies within an external covering of tough material. These are the pangolins, with their scaley chainmail armour made of keratin (the same material our nails and hair are made of), and the armadillos, with their bony shells, bound by collagen fibres and likewise covered in a layer of keratin scales. Rolled tight into a ball, with all their soft parts concealed, these mammals might as well be inedible rocks to most predators.

Clockwise from top left; an East Asian porcupine (*Hystrix brachyura*), desert hedgehog (*Paraechinus aethiopicus*), lowland streaked tenrec (*Hemicentetes semispinosus*), and a short-beaked echidna (*Tachyglossus aculeatus*).

Then there are the pincushions; those mammals that strongly discourage predation by inflicting pain. Hedgehogs and porcupines are the most famous and widespread spiky mammals. Australia and New Guinea have echidnas — long-snouted marsupials that hunker down in the ground, leaving nothing but their spiny backs exposed. There are also the little-known tenrecs of Madagascar — a family of hedgehog and shrew-looking creatures that aren't closely related to either — some of which have spines. All of these disparate mammalian groups separately converged on the same defensive strategy; modifying their fur into sharp, keratinized quills — evidence of an especially useful adaptation.¹ So perhaps it's unsurprising that a notoriously adaptable group of rodents, the rats, have gotten in on the trend.

Furry and Spiny Rats

Some 60 species of rats live the world over. Your typical rats are found in the genus Rattus, characterised by long-snouted faces, naked tails, and somewhat dumpy, furred bodies — they are differentiated from mice by their larger and heavier physiques. This group is technically known as "Old World Rats" because they're native throughout Europe, Africa, and Asia — however, the all-too-familiar brown rat (Rattus norvegicus) and black rat (Rattus rattus) have made themselves at home in the Americas as well. But don't worry, the New World has its native rats too; including pack, or wood rats (genus Neotoma), rice rats (genus Oryzomys), and cotton rats (genus Sigmodon) — they're just not nearly as prolific as the Rattus invaders.

You may not be inclined to cuddle any kind of rat, but you'd definitely have a better time with, say, a brown or wood rat than any of the appropriately named "spiny rats". These quilled critters don't form a single related group but are instead scattered throughout the rodent family tree. Each varies in their degree of "spininess". Many, like the spiny rats of Southeast Asia (genus Maxomys), simply have slightly bristlier-than-normal fur. Others, like the spiny rats from Japan's Ryukyu archipelago (genus Tokudaia), have more pronounced, grooved spines. The rainforests of South America, deadly as they can be, are home to bristly rats that live in the trees (genus Echimys), spiny rats that scurry along the forest floor (genus Proechimys), and prickly oddities that almost look made-up (Echimys chrysurus). But no rat species, in the Old World or the New, boasts spines as impressive as the armoured rat.

Clockwise from top left; a brown rat (*Rattus norvegicus*), black rat (*Rattus rattus*), hispid cotton rat (*Sigmodon hispidus*), and dusky-footed woodrat (*Neotoma fuscipes*).

Clockwise from top left; a Musschenbroek's spiny rat (*Maxomys musschenbroekii*), Napo spiny rat (*Proechimys quadruplicatus*), Amami spiny rat (*Tokudaia osimensis*), and artwork of a white-faced spiny tree rat (*Echimys chrysurus*).

The Armoured Rat

The armoured rat outdoes hedgehogs at their own game. Its body — otherwise quite typical for a rat — is covered in a coat of spines that can each grow as long as 3 centimetres (1.2 in). The species is sometimes considered a member of the Neotropical spiny rats (genus Proechimys) but due to its unmatched spininess among rats, it's typically placed alone in a separate genus; Hoplomys, from the two Ancient Greek words ὅπλον (hóplon), meaning "armour", and μῦς (mûs), meaning "mouse/rat".

It is still a Neotropical rat — that is, a rat that lives in the Neotropics. Its range begins in Central America, in southern Honduras, and trickles southwards, just reaching northwestern Ecuador but never spilling east of the Andes. Its world cycles through two distinct seasons, dry and wet. For four months, from mid-December to April, it rains relatively little. But the rat prefers its home lush and wet. And when it gets wet, it gets very wet — with the Chocó rainforest of western Colombia considered the wettest forest in the world. May marks the beginning of the wet season and brings an average rainfall of 2,600 mm (102 in) — 90% of all rain that will fall onto these pluvial forests.

The armoured rat revels in the downpour. It scampers through the rainforest alongside swelling streams that flow down steep slopes and wind between fallen logs. Pathways, elaborately constructed through the vegetation, ferry the rat safely on its nighttime commutes between its burrow and foraging grounds. It bounds along with a lopping gait — able to spring 22 cm (8.6 in) straight into the air — but it never ventures far from a river or wetland, since it can't tolerate dry habitats for long.

Its diet is largely fruit — bananas and mangoes, avocados and wild figs — which hang most abundantly at the beginning of the wet season. But it won't turn its head at a crunchy beetle or grasshopper. What the rat doesn't eat, it brings back to store in its burrow. This abode is built into the bank of a stream, consisting of a tunnel that extends some 1.5 to 2 metres (5 - 6.6 ft) to a cosy nesting chamber at the end, kept dry with a matting of vegetation — there's also a separate "restroom" chamber for defecation (since the armoured rat is a civilized rodent). This under-dwelling is also the safest place to raise a pack of pups.

While some armoured rats breed year-round, others will time their breeding to concise with the rain. Females totter about with bulging bellies between February to July, pregnant with a litter of one to three pups. The little ratlets are sheltered in the dark of the burrow and fed by their mother for some three to four weeks. By the time they're weaned off her milk, their fur has already begun to develop into brambles of stabbing spines.

You might expect a back full of bristles to dissuade most predators, but a few cunning hunters still stalk the armoured rat, including lithe wildcats like ocelots and jaguarundis, and various snakes, among them the largest of all vipers; the South American bushmaster. Few hedgehogs have to face such deadly foes. Without its "armour", the armoured rat would surely make for a more appetising meal, but it doesn't solely rely on its spines. Confronted with a threat, the armoured rat utters a forceful battle cry (“whee-unk”), but, if somehow that doesn't frighten its foe, the rat will drop its writhing tail to distract the attacker while it makes its getaway. Unfortunately, this is a one-time trick.

¹ The spines of hedgehogs, echidnas, and tenrecs are deeply rooted while the quills of porcupines can easily detach to impale the skin of an attacker.
You can learn more about hedgehogs, porcupines and their quills from the long-eared hedgehog!

**Where Does It Live?**

⛰️ Primarily in forests near water, but also in palm swamps and on abandoned farmlands.
📍 Central and South America; from northern Honduras to northwest Ecuador.

‘Least Concern’ as of 05 May, 2016.

IUCN

Size // Small
Length // 22 - 32 cm (8.6 - 12.6 in)
Weight // 220 - 820 grams (0.5 - 1.8 lbs)
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: 2 years (average in wild), up to 7 years (in captivity)
Diet: Omnivore
Favourite Food: Fruit 🍌
Class: Mammalia
Order: Rodentia
Family: Echimyidae
Genus: Hoplomys
Species: H. gymnurus

The armoured rat lives in Central and South America — from southern Honduras to northwestern Ecuador.

This rodent lives in tropical forests, usually near water, but it's also found in palm swamps and on patches of abandoned farmland.

Its diet is fruit; greatly enjoying bananas, mangoes, avocadoes and wild figs. But it spices things up with the occasional insect — a beetle or grasshopper — and some soft seeds and green plant matter.

It's known to cache extra food inside its burrow — usually a simple horizontal tunnel dug into the bank of a stream. Inside is a nesting chamber, made soft and dry with a matting of vegetation, and a separate chamber for relieving itself.

A mother rat raises her ratlets inside her burrow. They stay with her for three to four weeks, and by the time they've been weaned off of her milk, their fur has already begun to develop into stabbing spines.

The armoured rat's spines can grow as long as 3 centimetres (1.2 in), but sometimes they're not enough to deter a predator. In such cases, the rat might give a frightening yell (“whee-unk”), and if worse comes to worst, it can drop its tail to distract the predator while it runs away. Unfortunately, the tail doesn't grow back.

The armoured rat is usually placed alone in the genus Hoplomys — from the two Ancient Greek words ὅπλον (hóplon), meaning "armour", and μῦς (mûs), meaning "mouse/rat".

There are various other spiny rats scattered around the world and in different taxonomic families. There are the spiny rats of Southeast Asia (genus Maxomys), the spiny rats from Japan's Ryukyu archipelago (genus Tokudaia), as well as others from South America that live in the trees (genus Echimys) and scurry along the ground (genus Proechimys).