Interplanetary species

This article is based on canon information, but the article's title is conjectural and/or uses descriptions as the title, as there is currently no official name for the subject.

Concept art for multiple varieties of Spadehorn, an exotic creature native to Reach that resembles the bighorn sheep of Earth.

As space-faring sentient species began colonizing star systems throughout the Milky Way, many planets were discovered with thriving populations of identical or near-identical plant and animal species, some recognizable from the colonists' respective homeworlds. In many cases, this was a result of the Forerunner Conservation Measure and manipulation by the Lifeworker Rate. In other cases, the cause was not as clear.

On planets where native species were not identical, they largely tended to follow standard morphological baselines to those observed on Earth. Fish looked like fish, insects looked like insects. Amphibians, reptiles, avians, and mammals could all largely be grouped into the same class as their Earth counterparts, even if local environmental pressures caused them to evolve along alternative biological paths. For example, the Jiralhanae homeworld Doisac had a species of cattle which were used by the Jiralhanae similarly to Earth cattle, and the Kig-Yar homeworld Eayn had species of hawks and vultures. Some of the more exotic life forms could also be found distributed across multiple worlds.

Invasive ecology

"Atmospheric processors could nudge a generally suitable planet toward sustainability, but they couldn’t remake worlds."

— Halo: Contact Harvest

Agricultural livestock in a kiva on Reach.

In the process of terraforming worlds, humanity employed various methods to nudge local environments towards Earth-normal and sustain a growing population of colonists. Many of these involved the introduction of human agriculture and livestock, as well as forms of wild plant and animal life to balance ecosystems and atmospheric levels for human habitability. Some species were also likely introduced by accident after they stowed away aboard ships.

The following is a list of known Earth species that made their way onto alien planets through human action.

Flora Plant Locations introduced Agricultural crop Boundary, Harvest, Mamore, Reach Magnolias Harvest

Fauna Animal Locations introduced Agricultural livestock Boundary, Harvest, Reach, unidentified human colony Bats Harvest Crows Bliss Gophers Harvest Honeybees Harvest Owls Reach Starlings Harvest Wolves Reach, unidentified human colony

Earth-like ecology

The Earth-like forests of Circinius IV.

On other worlds, Earth-native species (or species which appeared visually identical) were discovered prior to modern human interference. On many planets, it was common to find terrestrial grasses, ferns, lichen, and algae. On others, more notable species were observed, sometimes dwelling alongside exotic, alien flora, other times part of ecosystems nearly identical to those of Earth.

The following is a list of known Earth species that exist on alien planets not as a result of modern human action.

Flora Plant Locations found Acacias Onyx Banana plant Arcadia Banyan trees Meridian, Onyx Black cottonwood Circinius IV Conifers Alpha Halo, The Ark, Delta Halo, Eridanus II, Heian, Nysa, Reach, Sedra, Trove, Warial, Zeta Halo Date palm Arcadia Douglas fir Reach Eastern white pine Trove Elephant ear Arcadia Hawthorn Circinius IV Hazelnut Circinius IV Huckleberry Circinius IV Juniper Concord Lamb's ear Arcadia, Trove Oaks Harvest Pacific dogwood Circinius IV Peppermint High Charity Red alder Circinius IV Sage Concord Sitka spruce Circinius IV Tobacco plant High Charity Vine maple Circinius IV Water lillies High Charity Western hemlock Circinius IV Western red cedar Circinius IV

Fauna Animal Locations found Butterflies The Ark, Reach, Trove, Zeta Halo Fireflies Reach

Exotic ecology

"There were these big damn plants, like tentacles. I swear, it was like the planet was fighting us, too."

— Lieutenant Caitlin de Sauveterre

Exotic plant life on Draetheus V.

Some forms of life were distinct from those found in Earth ecosystems, despite sharing (in most cases) morphological similarities. A number of these exotic organisms had similar ubiquity across multiple star systems. In some cases, life forms were discovered which resembled prehistoric fauna from Earth's Pleistocene epoch, and some may have actually been transplanted as a result of the Forerunner Conservation Measure, continuing to evolve long after they went extinct on Earth. Some exotic species, while first discovered on alien worlds, were transplanted to other planets as a result of interstellar trade.

The following is a list of known exotic species that existed on multiple planets and installations.

Flora

Plant	Name	Description	Locations found
	Swamp tree	A large bioluminescent plant found around Flood containment facilities on Halo rings and on the Covenant Holy City, High Charity.	Alpha Halo, Delta Halo, High Charity

Fauna

Animal	Name	Description	Locations found
	Blind wolf	Predatory pack hunters found on various Forerunner installations that primarily rely on sound to direct their attacks.	The Ark, unidentified Halo ring
	Brontothere	Originally found in east Africa in 97,445 BCE. Following their indexing by the Forerunners, brontotheres in the modern era can be found in a variety of biomes on Forerunners installations.	Prehistoric Earth, unidentified Halo ring
	Kig-Yar parasites	The Kig-Yar occasionally suffered parasitism from feather mites, tapeworms, and fleas, which were common nuisances across their colonies.	Kig-Yar colonies
	"Nightmare eel"	A large sea creature found in the Eridanus and Bhaakto systems in deep oceans where it hunts seafloor-dwelling organisms alongside the Paelosur.	Beta Gabriel, Alluvion
	Quadwing	A pterosaur-like creature with dual sets of wings that is ubiquitous across many Forerunner installations.	The Ark, Delta Halo, unidentified Halo ring
	Merse	Territorial aquatic creatures that resembled giant lily pads, they were placed on many worlds by Forerunner Lifeshapers, particularly the Librarian.	Bastion, prehistoric Earth, Nomdagro
	Moa	Large, flightless birds named after and resembling the extinct moa of Earth. They were domesticated by humans for use as pets and cuisine, and as a result are found on several other worlds. They are close to extinction on their native homeworld of Reach after the ecological catastrophe caused by the Fall of Reach.	Casbah,, Earth, Gannick 22, Reach
	Olfmeri	Airborne cetacean-like creatures that can be found on many Forerunner installations, known for their enigmatic grace and beauty.	The Ark, unidentified Halo ring
	Paelosur	A sightless cetacean found in the oceans of multiple worlds across the Inner and Outer Colonies, alongside the Qothal.	Beta Gabriel, Alluvion
	Pheru	Originating from Faun Hakkor, these friendly creatures were domesticated by ancient humans and Forerunners and spread across many of their worlds as pets, ultimately becoming a vector for the first Flood infection in the Milky Way.	Faun Hakkor, Forerunner ecumene
	"Space bird"	A flying species found on multiple human and Forerunner worlds.	Erebus VII, Eudemon, Requiem, Partition, Talitsa, Terceira
	Thorn beast	A docile herd herbivore used for food and other resources by the Covenant and the Jiralhanae in particular.	Doisac, Covenant worlds

Production notes

• The oxyaena was a creature fully modelled and textured for inclusion in Halo Wars. The Oxyaena was a prehistoric Earth mammal that lived during the Eocene.
• Halo: Reach featured a number of cut lifeforms which resemble highly speciated Earth organisms.