Flies are one of nature's scavengers, so they feed on everything from decaying meat and feces to rotting fruit and other insects. Most use sponge-like mouth parts and a specialized straw-like structure, known as a proboscis, to slurp up their food. This strategy works remarkably well for meals that are already in liquid form. But what about solids?
It turns out that flies begin such meals by vomiting on them. Their vomit contains a mix of saliva, enzymes, and digestive juices, which make short work of rotting apples or bits of decaying hamburger. Those flies that feed on other insects use sharp, blade-like structures like mandibles to pierce their skin first; they then proceed to suck their vital juices. They also use the many fine hairs that cover their mouth parts to get a small taste of the food they happen to be walking on.
Fungi come in all shapes and sizes. While most fungi live off decaying matter in the soil, others form symbiotic relationships with various plants, insects, and algae, providing a source of food and nutrients in exchange for a habitat and protection. In some cases, those relationships are rather one-sided.
The genus Cordyceps is made up entirely of endoparasitoids--parasites that develop inside of their host. These invade an insect, replacing its tissue and organs with their mycelia (a mass of thread-like hyphae that absorb nutrients from the environment) and stroma (a stalk-like fruiting body).
Cordyceps unilateralis, the species shown here, is able to control its ant host from within, forcing it to climb up a plant and settle near the top, whereupon the ant dies. By then, the spores attached to the fungus' fruiting body, which has emerged from the ant's head, have almost fully matured. When the time is right, they rain down on more unsuspecting ants, restarting the cycle.
Clams are among a large group of species, including sharks and whales, that feed by straining out bits of food from seawater. Like all clams, the giant clam, Tridacna gigas, pumps in water through a siphon, and transports it to the gills through the beating motion of short, hair-like cilia. A layer of mucus on the gills catches any food particles, and they are moved to the clam's mouth. A second siphon expels the filtered water.
The clam has another trick up its shell to supplement its diet. Thousands of tiny algae called zooxanthellae--responsible for the beautiful colors--reside within the clam's mantle tissues and photosynthesize during the day, when the clam opens up. In exchange for providing their host with an additional source of carbohydrates, the zooxanthellae get shelter and protection from predators.
When a team of researchers from the Monterey Bay Aquarium Research Institute descended into the nearby Monterey Canyon to study a gray whale carcass, they didn't expect to see much except some decaying bones and a few scavengers. What they found instead were large communities of what looked like bright red feathers surrounded by tufts of algae.
Upon closer inspection, they realized the "feathers" looked a lot like the plumes of giant tube worms--and in fact they perform the same role: absorbing oxygen from seawater. The feathery things belonged to two new species of worms--Osedax rubiplumus and Osedax frankpressi (seen in the picture)--which use them as gills. The worms were were all female; the male worms, they soon discovered, lived inside the females' bodies and were little more than microscopic bundles of sperm.
Like tube worms, these creatures lack mouths and a full digestive tract. They also form a symbiotic relationship with a strain of bacteria that lives at the base of their bodies. The bacteria infiltrate the whale bones and break down their oils and fats to provide food for their hosts. In return, the worms share some of the oxygen that they take up from the surrounding water.
Imagine having a head that's too small to swallow your food. That is the dilemma facing the moray eel, a predator famous for its nasty bite and ability to devour large prey. Because of its relatively small head, the eel can't create the suction that most bony fishes need to swallow their prey.
Fortunately, the eel has come up with a neat strategy to circumvent this problem: an extra set of jaws, known as the pharyngeal jaws, located deep in its throat. After firmly grasping its prey with its front teeth, it extrudes its pharyngeal jaws (yes, just like Aliens) to drag it to the back towards the stomach.
The moray eel also has a strategy to handle still larger prey: It ties itself in a knot around its victim and proceeds to rip into it, biting off large chunks at a time.
The giant tube worm (Riftia pachyptila) lives around hydrothermal vents, which are formed by superheated, mineral-rich water coming into contact with cold seawater. They can grow up to eight feet in length.
While they lack a mouth, stomach, intestines, and anus, they do have a red plume that contains a lot of blood vessels and pulls nutrients like carbon dioxide, oxygen, and hydrogen sulfide from the water.
These nutrients are used by bacteria that live deep inside the tube worm's trophosome to synthesize a variety of organic compounds. The worm then feeds on these chemicals, though exactly how it does so still is not entirely known.
When times get tough, the tough join forces. At least that's the tactic employed by dictyoselids, a group of unicellular slime molds. When food supplies run low, they unite to form a multicellular entity, known as a pseudoplasmodium, or slug, to conserve resources. Once the slug finds the right environment and settles down, it forms an elongated stalk comprising many spores.
The individual spores are dormant slime molds that activate once there's food again. To feed, individual molds engulf bacterial cells whole through a process known as phagocytosis. Dictyoselids surround their prey with their pseudopods--small extensions of the cell membrane that are also used in locomotion--and internalize them in compartments called vacuoles. Enzymes in the vacuoles then digest the bacteria, after which the molds absorb the nutrients.
In the image, a slime mold (shown in white) is engulfing a yeast cell (shown in red). The green enclosure is a vacuole.
The starfish may not look the part, but it is a formidable predator. Its favorite prey includes mussels, oysters, and other shellfish.
All starfish come equipped with two stomachs in their mouths: the cardiac stomach and the pyloric stomach. When a starfish encounters its prey, it uses the tiny tube feet that line the underside of its arms to pry open the shell.
A small opening is all it needs to spit out its cardiac stomach and insert it into the victim's shell. The bivalve sits helplessly as the digestive juices slowly decompose its soft tissues.
Once the process is complete, the starfish takes back its cardiac stomach and moves the partially digested food to its pyloric stomach, then on into the intestines.
Some of the strangest eating habits belong to plants rather than animals. While most extract vital nitrogen from the soil, carnivorous plants like sundews (shown in the picture) obtain it by trapping and devouring small insects.
The sundew gets its name from the sticky secretions that adorn its hair-like glands. Flies and other small insects, attracted by the secretion's sweet smell, are lured to the plant's glands, only to find themselves hopelessly stuck.
Try as they might to escape, the insects eventually succumb to a combination of exhaustion and asphyxiation as the sundew's mucilage seeps into and clogs their spiracles--the holes in their skin through which they breathe. The sundew slowly rolls up the edges of its leaves, further ensnaring the trapped, and releases a cocktail of digestive juices containing potent enzymes, which slowly begin to decompose the prey. After a few days, the insects are reduced to a rich nutrient soup, which the sundew happily absorbs.