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How Does Life Work?

Symbiosis and Interliving
What For? How?

click to find answers

For Cleaning
For Protection & Shelter

Ants:Masters of Interliving

Giraffes and Acacias
For Reproduction
Wheels Within Wheels
To Pioneer & Fix Nitrogen

Interliving for Food


Remora fish on the belly of a shark, waiting for scraps
Leaf-cutter ants garden fungus to eat
and feed leaves to the fungus. The little ant atop the leaf is a small warrior.
Barnacles living on the fin of a humpbacked whale. Many whales have barnacles glued to their lips. One species of barnacle lives only glued onto the barnacles that live on whale-lips.
A barnacle open and filter-feeding. As whales move through water, barnacles have a continuously changing menu.



Epiphyte lichen living on an alder branch in a rainforest in a mountain valley. The algal partner in this Lobaria lichen is a nitrogen-fixing cyanobacterium (nostoc). These lichens are a major source of nitrogen in old-growth forests. The lichen's food is sunlight, plus minerals from the branch and mosses. The forest's food is nitrogen. Epiphyte licorice ferns living on a temperate rainforest tree trunk with mosses. They get sunlight at this height, and the moss substrate serves as water source. Thery don't hurt the tree: like all epiphytes, they use trees as homes with good light.
A huge number of epiphytes growing on a tree branch in a tropical rainforest
Coral reef polyps open and filter feeding. Reef-building corals need more carbon to build reefs than filter-feeding provides. So they found a partner. See photo on right.
Photosynthetic algae called zooxanthellae live inside each coral polyp and make food which the corals cannot thrive without.

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Interliving for Cleaning and Food
An oxpecker bird eating ticks from a pleased antelope. Magpies do the same task for sheep and cattle in temperate zones.
A cleaner shrimp at his station on a coral reef, waiting for a customer A cleaner wrasse eating parasites from a hatchetfish that has come to be cleaned

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Interliving for Shelter & Protection


An oakleaf gall made by a tiny wasp that pollinates oak flowers. When she stings a leaf to lay an egg, she also injects chemical instructions to grow a gall that will feed and protect her larva. Notice the emergence hole at center.
Fig wasps ready to emerge from a fig. The wasps will leave to pollinate fig flowers, which are, oddly, inside the fig. Notice the long ovipositor which pierces the green fig to lay eggs and pollinate at the same time. Their larvae will thrive inside the fig, protected. For more, go here.
A niche in a dead tree made by a pileated woodpecker. A chickadee spent many winter nights in this niche, out of below-zero winds. It left behind many droppings and one feather. Woodpeckers make new nest cavities in trees each year, which are later used by many birds. Interlivings are not intentional or conscious the way we humans think we are. Goldenrod gall. A little fly pierces the growing tip and lays an egg. When the egg hatches the grub begins to eat, which chemically stimulates the plant to grow a swollen ball in its stem. This gives the grub food and protection until it is an adult and can chew its way out and pollinate goldenrod flowers. The gall above was opened last winter by a downy woodpecker, which specialize in grub extraction. Most grubs do become adults. Adults hang around the goldenrod top, live about 2 weeks, mate, lay eggs, and die.
This weevil in the rainforest shows how lives live on and with each other. The lichens on its back are themselves small ecosystems where live myriad small creatures, from water bears to nematodes to protozoans, and they all have bacteria living in their guts. All macro-life, whether tree or insect or you, is a vast home for many interliving organisms. Adapted from E.O. Wilson, Biophilia

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Ants: Masters of Interliving

Acacia trees grow thorns to repel herbivores, which works on mammals, but not on insect leaf-eaters or vines. So, an interliving with ants was eventually born.

Some acacias adapted swollen thorns to grow large enough to be homes for ants. If anything, mammal or insect, starts eating leaves, ants swarm it and drive it away. If a vine or epiphyte tries to colonize, the ants sting it until it dies.
Acacia gives ants more than thorns to live in. She feeds them sweet sap through special organs called nectaries.
Here three ants sip nectar from their host tree.
Beltian bodies grow at the tips of acacia leaves and provide ants oils and proteins. This incredible adaptation suggests how very long ants and acacias have been partners. Ants also attack vines and epiphytes. When this small acacia's ants were killed, the vine quickly overwhelmed the tree, which died for lack of light.
A remarkable mutualism has evolved between an ant, a butterfly caterpillar, and an acacia in the American southwest. The caterpillars have nectar organs the ants drink from, and the ants allow the caterpillars to eat acacia leaves. The ants provide protection for both plant and caterpillar. Photo © Gregory G. and Mary Beth Dimijian
Butterfly-ant symbioses have been found in two butterfly families but it is most striking in the Lycaenidae. The Lycaenidae make up approximately 30% of known butterflies, and within the family more than half of the species interlive as caterpillars with ants. The ants receive sugars and amino acids from the caterpillars.
Ants "farm" aphids, tiny sapsucking insects. Ants feed on sweet nectar from the aphids, protect them from enemies, and even move them to new pastures. A single ant shepherd surveys its herd of aphids
Here ants farm mealybugs on a leaf, which secrete honeydew for the ants.

Ant tending leafhopper larva,
as two adult leafhoppers
emerge from pupa stage below.
Amazing photo © Leon Higley


Click to enlarge the amazing ant images below,
copyright © Dale Ward. Used by permission.
More at


Dorymyrmex bicolor eating honeydew
from a barrel cactus
click to enlarge
Dorymyrmex bicolor taking honeydew from newly molted leafhopper young
click to enlarge
Dorymyrmex bicolor taking honeydew from adult leafhopper
click to enlarge
Detail of nectary on mesquite. The nectar is seasonal. Click to enlarge
This honeypot ant is a living larder filled with honeydew to insure colony survival.
click to enlarge
ants tending aphids on milkweed leaf
in desert southwest
click to enlarge
ant eats nectar on a sunflower leaf
click to enlarge
notice how viscous and sticky the sunflower nectar is
click to enlarge

ants on mesquite tend small sucking insects, such as scale, for honeydew
click to enlarge
native fire ants drinking from nectaries on barrel cactus click to enlarge

Some ants, mostly tropical, but also some in SW desert US, farm fungus. Foragers carry leaves and stems to the nest. Others lick it with anti-bacterial saliva, chew it into mushy pellets and innoculate it with strands of the fungus they have depended on for 25 million years. This fungus does not exist outside ant nests. They are mutually interdependent.

Like most ant species, leafcutters have different sizes of workers in the nest. Some have tiny fierce minima workers that ride the heads of foragers to protect them from parasitic flies that lay their eggs on ant necks so the larva can eat the ant's brain.

Some leaf-cutters have nests as deep as 18 feet with many millions of inhabitants.
All are the children of the queen ant. In one genera, she is as large as a mouse (see below)

Trachymyrmex arizonensis take greens to nest, grow symbiotic fungus on it,
eat the fungus.
click to enlarge
Huge Atta species queen on one fungus garden in her nest in Central America

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Giraffes and Acacias

All acacia trees have thorns. Those pictured above, with ants, have swollen thorns. Most acacias on the African savannas have unswollen thorns.

If acacias are the most common tree on a savanna, giraffes must eat acacia leaves. Together they have evolved a system for coexistence.

Acacia trees and a giraffe are perfect symbols of African savannas. Acacia leaves and unswollen thorns.
Giraffes can eat around the thorns, for awhile. See text below pictures. It is no accident that there is no foliage below the reach of a giraffe's neck.
Giraffes have a long prehensile tongue that cleverly winds around leaves and plucks them without even touching thorns . A satisfied giraffe, with a mouthful of acacia leaves. A giraffe puts away about sixty-five pounds of acacia leaves on a good day.

When a giraffe begins to browse acacia leaves, the tree immediately begins pumping alkaloids into all its leaves which make its leaves nasty-tasting and sickening. So the giraffe only gets to eat a few acacia leaves from that tree. Here is where the story gets interesting.

When the acacia begins its chemical defense, it releases a signal into the air, and all of the acacia trees downwind of the injured tree immediately begin to pump their own leaves full of poison too. You get a picture of a lot of hungry giraffes.

Giraffes, however, have found a way to browse acacias. They begin upwind and graze against the wind. They can still only get a few leaves from each tree before the leaves become too bitter, but as long as they work with the wind, they do get a meal.

This relationship is clearly not symbiosis in the traditional sense, but just as clearly it is co-evolved interliving. Although it is based in self-interest, the cooperation here is real. Both members of this collaboration get what they need.

This giraffe/acacia pattern of interliving turns out to be a common one. It’s quite ordinary, we are beginning to discover, for plants to be responsive to animals (especially insects) in many ways.

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Interliving to Aid Reproduction

Cedar Waxwing eating berries. The seed will pass through its gut scarred just enough to ensure germination.

This magnified seed evolved its hooks to catch on fur and feathers so it could spread far and wide.
This dung beetle rolls its nursery to a burial site. She has laid an egg inside.
Burdock fruit covered with tiny hooks. The inventor of Velcro used burdock seedhead as a model.
This bee is already loaded with pollen, but takes time for one more daisy.
A honeybee pollinates a goldenrod
The mockingbird benefits from berries that ripen in synchrony with fall migration. It will disperse the plant's seeds for miles, so both bird and bush benefit.

This orchid interlives with both mycorrhiza and insects. Its flower mimics a female wasp, and combined with a scent of the female wasp that the plant creates, the orchid gets pollinated.


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Termites: Wheels Within Wheels

Termites are incredible insects. They are keystone species in African grasslands and savannas.

There are two groups of termites. Let's call them Loggers and Farmers.

Logger termites live by eating wood, but cannot digest it. Inside their gut live many protozoans who swallow bits of wood as it passes through. But they can't digest cellulose either. The protozoans rely on a certain bacterium in their own tiny gut to transform wood into an energy source for a) themselves, b) the protozoan, and c) the termite itself. Interliving organisms nest inside each other like Russian dolls.

Farmer termites eat wood also, as much as they can. But they don't even try to digest it. Instead, they carry it into the mound where they have fungus farms, and they regurgitate all their wood onto the fungus, which digests it. The termites then eat the tiny fruiting bodies of the fungus. Evolved termites interlive with fungus pretty much like humans interlive with corn.

A fungus garden inside a Farmer termite mound
termites en masse
Termite warrior castes have massive mandibles
Termites don't get sun. In deserts they build covered above-soil tunnels to get to dead wood without dying from sun.
A single termite, enlarged
The Trichonympha protozoan that lives in the Logger Termite gut. Bacteria inside this creature actually digest the cellulose. A symbiote within a symbiote within a termite!

For humans, termites are a danger to buildings. Together with their interliving partners, termites play the vital role of decomposing wood. Most biomass in deserts is dead shrub wood. Without termites there would be few life nutrients recycled in deserts.

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Interliving to Pioneer and Feed: Lichens

Until recently, lichens were the only example of Interliving that science was generally aware of. But lichens were regarded as an oddity; they were once called "the trash of the vegetable world. " In fact, the lichen interliving of algae and fungus is uniquely valuable in several biomes. In old growth forests, lichens are a primary source of nitrogen, a critical plant nutrient. In desert ecosystems lichens do the same job. Lichens are good ecological canaries, for most will only grow where the air is not polluted.

Old man's beard lichen dangles from Douglas fir.
Like many organisms, lichens find tree bark a clean, well-lighted place to live.
These lichens pioneers on desert rock are slowly eating bits of rock away. A lichen on a twig. It likes it there.
Lichens and moss colonizing a cedar stair tread on a deck. Algae are also present, showing 3 "stages" of succession Reindeer moss lichen of the taiga and tundra, nutritious food of caribou.
Lichens pioneering a granite boulder have all the time in the world to turn it into soil. On northern mountains and once-glaciated areas, geologists use lichen-dating to study advances and recessions of glaciers. Some lichens are extremely old. Lichen on Utah slickrock, which is porous and a fair source of water in the high desert. Lichens have no problem estivating (going dormant) when they dry up.



It becomes clear, as we look at example after example of Interliving, that these arrangements for survival have evolved. In other words, they have resulted from organisms finding mutual advantage in living together and in response to each other over long periods of time. They have become so good at cooperating that in many cases they cannot live alone. It is evident that species do not evolve alone; they evolve in response to one another. The community, not the species alone or the pair of species, is what evolves. We are barely beginning to glimpse how densely interwoven are the mutual ties within living communities. Reciprocity is the rule of life, not the occasional exception.


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Explore Further


Explore the Biosphere

Biosphere: Introduction
Biosphere as Place: Introduction
Biosphere as Ocean: Life Zones
Biosphere as Ocean Floor: Benthic Biomes One
Biosphere as Ocean Floor: Benthic Biomes Two
Biosphere on Land: Terrestrial Biomes
Biosphere on Land: Anthropogenic Biomes
Biosphere as Process: Introduction
Biosphere Process: Floating Continents, Tectonic Plates
Biosphere Process: Photosynthesis
Biosphere Process: Life Helps Make Earth's Crust
Biosphere Process:
Rock Cycle--Marriage of Water and Rock
Biosphere Process: Marriage of Wind and Water
Biosphere Process: Gas Exchange
Biosphere as An Expression of Spirit
The Ecological Function of Art
The Earth Goddess
The Tree of Life
The Green Man
Earth Art
Biosphere as Community
Biosphere Microcosm: Bacteria and Archaea
The Procaryote Domain
Biosphere Microcosm: Germs
Biosphere Community: The Eucaryote Domain
Biosphere Community: Protists 1: Algae
  Biosphere Community: Protists 2: Protozoa
Biosphere Community: Plants: What's New?
Biosphere Community: Kinds of Plants--Major Groups
Biosphere Community: Plant Defense
Biosphere Community: Plant Pollination
Biosphere Community: Plant Seed Dispersal
Biosphere Community: Kingdom Animals
Biosphere Community: Kingdom Fungi
Biosphere Community: Six Great Extinctions
Return to Ecology Index


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