Animals That Start With X

The best-known animal beginning with X is the xerus, an African ground squirrel. Close behind it are Xenopus the African clawed frog, the X-ray tetra, and the xoloitzcuintli, Mexico's hairless dog breed.

That is close to the whole list, and it is worth saying plainly: X is by far the hardest letter in the alphabet for this. Of the 11,227 bird species in the IOC World Bird List, exactly five have English names beginning with X. Of the 6,871 mammal species in the Mammal Diversity Database, six do. Most "animals that start with X" lists pad themselves out with genus names, and this one will too — but it will tell you which is which.

The ones with real English names

X-ray tetra (Pristella maxillaris). A small South American characin from the Amazon and Orinoco basins, reaching about 4.5 cm. Its body is translucent enough that the backbone and swim bladder are visible from outside, which is where the name comes from. Common in home aquariums.

Xoloitzcuintli. The Mexican hairless dog, pronounced roughly "show-low-eets-QUEENT-lee" and usually shortened to xolo. The name combines Xolotl, the Aztec god of fire and lightning, with itzcuīntli, meaning dog. It comes in toy, miniature and standard sizes, from about 10 to 55 pounds, in hairless and coated varieties that can appear in the same litter. The American Kennel Club first registered one in 1887, dropped the breed in 1959 when numbers collapsed, and restored it to full recognition in the Non-Sporting Group in 2011. You can find it and several hundred others in our random dog breed generator.

Xantus's hummingbird (Basilinna xantusii). A hummingbird restricted to the southern half of Baja California. Named for John Xantus, a Hungarian naturalist who collected in Mexico and California in the 1850s and 1860s.

Xingu silky anteater (Cyclopes xinguensis), Xingu bristly mouse, Xochimilco marsh rice rat, Xanthippe's white-toothed shrew, Xico deermouse and the xeric four-striped grass rat. These six are the entire set of mammals whose primary common names start with X. Notice the pattern: Xingu is a river in Brazil, Xochimilco is a district of Mexico City. The letter arrives through place names.

Xingu scythebill, Xingu scale-backed antbird, Xinjiang ground jay and Xavier's greenbul are the other four X birds, alongside Xantus's hummingbird. Again: two Brazilian rivers, a Chinese region, and a person.

The ones that are genus names

These are real animals, but the X comes from scientific nomenclature rather than everyday English.

Xerus. African ground squirrels. Under the current Mammal Diversity Database taxonomy the genus holds only the unstriped ground squirrel, Xerus rutilus, with its former relatives such as the South African ground squirrel moved into Geosciurus. Older references keep all of them in Xerus, which is why the name is so widespread on lists like this.

Xenopus. Twenty species of African clawed frog from sub-Saharan Africa, entirely aquatic, with claws on the hind feet. Xenopus laevis and Xenopus tropicalis are among the most heavily used laboratory animals in developmental biology. The genus is also strikingly polyploid, with some species carrying up to twelve sets of chromosomes.

Xantusia. Night lizards of the southwestern United States and Baja California. The family Xantusiidae has roughly 34 species across three genera. They give birth to live young, have transparent immovable eyelids like a snake's, and are extreme microhabitat specialists — a particular kind of rock crevice, a particular fallen log. Our random reptile generator covers lizards, snakes, turtles and crocodilians.

Xenops. Small Neotropical ovenbirds. Seven species carry the word in their English names — streaked xenops, great xenops, slender-billed xenops — though it sits second rather than first.

Xylocopa, the carpenter bees, which bore nest tunnels into dead wood. Xiphias, the genus of the swordfish. And Xiphosura, the horseshoe crabs, which are not crabs at all but chelicerates, closer to spiders than to anything crustacean.

Xenarthra is worth knowing as a group name. It covers the 31 living species of anteaters, sloths and armadillos, and means "strange joints" — a reference to the extra articulations in their spines that no other mammal has. An armadillo is a xenarthran.

Why the list is so short

English has very few native words beginning with X. Almost everything in the dictionary under that letter is a Greek borrowing — xylophone, xenon, xenophobia — or an abbreviation like X-ray. Common animal names tend to be plain descriptive English or borrowings from local languages, so they inherit that scarcity directly.

Scientific names are more generous, because Greek roots beginning with X are productive: xanthos (yellow), xenos (strange or foreign), xeros (dry), xylon (wood), xiphos (sword). Plenty of genera start with X. But a genus name only becomes an everyday animal name occasionally, and usually only when the animal has no other name in general use.

That leaves place names and people's names as the main route into the letter. Xingu, Xinjiang, Xochimilco, Xantus, Xavier — nearly every genuine X animal traces back to one of those.

One that no longer counts

Xantus's murrelet used to appear on every list of X animals. In July 2012 the American Ornithologists' Union split it into two species, Scripps's murrelet and Guadalupe murrelet, on the basis of plumage, calls, genetics and a lack of interbreeding where the two meet. The name is no longer valid for any living species, so if you see it listed, the source is over a decade out of date.

The short version

For a school project or a quiz, xerus, Xenopus, X-ray tetra and xoloitzcuintli will serve. If you need something with a real English common name, the X-ray tetra and the xoloitzcuintli are the two safest answers.

To pull species from a much larger pool than one letter allows, try the random animal generator.