THE NATURALIST’S NOTEBOOK: What’s on the menu?
Exotic recipes from around the animal kingdom
CORRECTION TO THIS ARTICLE: A previous version of this article indicated that Charles Darwin promptly died from Chagas’ Disease, while his death is only speculated to have been caused by this disease.
Assorted small rocks
Many birds eat rocks. That sparrow pecking away at the sidewalk may be after sand and gravel, not just crumbs. The reason for this geophagy is that birds don’t have teeth, so they grind up their food using an organ called a gizzard, which is right next to the stomach. The gizzard must be filled with grit and small stones to break up the food while the gizzard churns.
In general, animals can’t photosynthesize. But there is at least one exception: a sea slug of the species Pteraeolidia ianthina. Sea slugs (also called nudibranchs) may be the showiest creatures on Earth. They look like a cross between a slug and a snowflake, and many species have such bright colors that they appear to glow. This particular one is blue-green, and it is filled with little algae that photosynthesize for it. Like a plant, it can sit in the sun all day and simply make its own food.
Poison ivy berries
Don’t try this at home. Most people are allergic to the chemical urushiol, which is found in all parts of the poison ivy plant, including the ghostly white berries. Surprisingly, however, urushiol is only a problem for us humans, as well as for some other primates. If you are a bird, poison ivy berries are tasty and nutritious, and a great way to stock up on food before the winter.
Disquieting as it may be, your own body is food for a large number of tiny creatures. The eyelash mite is one of them, a microscopic organism (1/3 of a millimeter long) that is found exclusively in the hair follicles of humans, especially around the face. About half of the population has them, and they don’t generally do any harm. But they are there, eating, sitting around, having sex on your eyebrows, and eventually dying. Curiously, though, they don’t poop at all; instead, they store up all their waste inside their bodies.
Birds in New England have a hard time during the winter. It’s cold and the food options are limited. There are some seeds and berries, but the insects have mostly gone into hiding or will hatch from eggs in the spring. The golden-crowned kinglet is a tiny bird whose song is a high-pitched squeak. It eats only insects, and it sticks around for the entire winter, rather than migrating south. This seems like a bad combination, but the kinglet is saved by a moth called the one-spotted variant. The caterpillars of this moth want to get an early start on eating leaves in the spring, so they hatch from their eggs in the fall and then stay out all winter on the branches of trees. Unlike most caterpillars, they can freeze solid with no ill effects, and they are camouflaged to look like twigs. Kinglets rely on these frozen caterpillars for food, hunting them diligently until spring, when the menu diversifies once again.
The shell of a dead tortoise
In Florida, there is a kind of tortoise called the gopher tortoise. The males fight with each other if they want the same female, and in these fights, one of the tortoises can get flipped over onto its back. In the sun, sometimes a flipped tortoise will die of heat and exhaustion before it can right itself. Now is the moment when the moth Ceratophaga vicinella steps in. It flies over and lays eggs on the dead tortoise, and little caterpillars hatch. They don’t eat the body of the tortoise. Instead, they work away at the shell. If you tried to pick up the tortoise at this point, you would discover that it is anchored to the ground by a network of silken tubes, within each of which a caterpillar is hiding and munching on tortoiseshell.
A number of birds live their whole lives at sea, eating things like fish and the carcasses of whales that float to the surface. Such birds, including albatrosses, petrels, and shearwaters, don’t come to land at all except to nest. As Tennyson’s Ancient Mariner discovered, the sea contains “water, water everywhere, but not a drop to drink.” Why isn’t this a problem for the albatross? Turns out that seabirds have a special organ called the salt gland, which concentrates the salt in seawater and excretes it through the nostrils at the base of the beak. This allows the albatross to drink nothing but saltwater.
There is a group of insects called “true bugs”. They include the stink bug, cicada, and aphid, and are technically the only insects that one should refer to as “bugs”. What sets them apart from other insects is their mouthparts: they can feed only through a stiff straw, which they normally keep folded away underneath the body. In most bugs, the straw is used for drinking the sap of plants, which is why gardeners hate aphids. However, some bugs drink the juices of animals instead. The ambush bug hides inside a flower and grabs any butterfly or other insect that happens by. Since most insects are not naturally drinkable, the ambush bug injects them with liquefying enzymes before inserting its straw and sucking them up. What’s left is a shriveled carcass that is barely recognizable.
A few of these carnivorous bugs attack mammals, including humans. Darwin experimented with one of these, an assassin bug from South America. He was curious to see what happened when the insect bit him, so he let it bite him repeatedly. As it turned out, that particular species carries a nasty illness called Chagas’ Disease, which is speculated to have caused Darwin’s death.
The Namibian desert is an unspeakably dry place. It never rains, but the desert is next to the ocean, which means that fog appears once or twice a month, rolls over the desert without condensing into droplets, and disappears again. There is a beetle in the genus Stenocara that manages to lives here. To obtain moisture, it waits for the fog to come, then uses its own back as a water-gathering device. Hydrophilic bumps on the beetle’s carapace serve to condense water, and hydrophobic troughs then channel the water into the beetle’s mouth. The technology on this beetle’s back is so advanced that the U.S. Army is working to replicate it.