40 Fun Facts About Life Cycles

Which reef fish, made famous by Finding Nemo, has a breeding male that turns female when the group's female dies?

Clownfish live in a strict size ranking around one anemone, so when the female is lost the male changes sex and the largest non-breeder steps up as the new male.

In which fish does the male carry the female's eggs in a pouch on his body until they hatch?

Seahorse fathers carry the eggs for 9 to 45 days, then release fully formed but very small young into the water.

Which sea animal has a species nicknamed 'immortal' because the adult can revert to its juvenile polyp stage?

Jellyfish of the species Turritopsis dohrnii can turn back into a seabed-bound polyp after reaching maturity, then grow up all over again.

Which cold-water fish, the longest-lived vertebrate known, is thought to reach breeding age at around 150 years old?

Greenland shark lifespans are estimated at 272 years or more, and the pups are born alive after a pregnancy thought to last 8 to 18 years.

Which North American insects spend 13 or 17 years underground as juveniles before emerging together in huge broods?

Cicadas of the periodical kind may owe those prime-number waits to their enemies: one idea is that 13 and 17 years are hard for predators with shorter cycles to match.

Which bird's male alone warms its one egg through the Antarctic winter, eating nothing for over two months?

Emperor penguin males lose around 12 kg during the fast, and in every other species of the family both parents take turns on the egg.

Which Australian mammal lays eggs instead of giving birth to live young, a trait shared only with echidnas?

Platypus eggs place the animal among the monotremes, and the egg-laying, beaver-tailed creature baffled the first European naturalists who examined it.

Which fish hatches in freshwater streams, matures in the ocean, and then swims back upriver to its birthplace to breed?

Salmon of every Pacific species die within days or weeks of spawning, and their bodies feed the streams where the next generation will hatch.

Which sea animal's mother guards her eggs in a den until they hatch and then dies, as the father already has?

Octopus parents breed just once: in most species the male dies after mating, and the female after tending her eggs to hatching.

What is the name for the legless, tailed young of a frog, a word that comes from 'toad' and 'head'?

Tadpole bodies are rebuilt for land: the tail is absorbed into the body, and the gut shortens as a plant diet gives way to hunting.

What is the name for a butterfly's hard-skinned pupa, a word that comes from the Greek for gold?

Chrysalis cases of many butterflies have a metallic gold sheen, which earned the name, while a cocoon is a separate silk casing spun mostly by moths.

What is the common name for the leaf-eating larval stage of butterflies and moths, known for its voracious appetite?

Caterpillar growth is explosive: a tobacco hornworm multiplies its weight ten-thousandfold in less than twenty days.

What is the name for the young of insects such as crickets and cockroaches, which resemble small wingless adults?

Nymph stages skip the pupa entirely, so the insect reaches adulthood through a series of gradual changes instead of one dramatic transformation.

Monarch butterfly larvae feed only on which plant, whose toxins make the insects taste bad to predators?

Milkweed leaves are where the females lay their eggs one at a time, and the plant's cardiac glycosides stay in the insect's body as a chemical defence.

What is the common name for the larva of a housefly or blowfly, used in forensics to estimate time of death?

Maggot development runs to a predictable timetable, so the stage reached by those found on a body helps investigators work out how long ago the person died.

Silkworms, the larvae of the domestic silk moth, feed almost entirely on the leaves of which tree?

Mulberry leaves give off an odour that attracts the larvae, which prefer the white species of the tree above all others.

Which insect's adults cannot feed, with the females of one species living for less than five minutes?

Mayfly adults exist only to breed: their digestive systems are filled with air, and all the eating is done earlier, during the underwater young stage.

Which biting insect lays its eggs in stagnant water, where the larvae hang at the surface to breathe through a siphon?

Mosquito life is mostly aquatic: the egg, larva and pupa all develop in water, and only the winged adult leaves it.

Which insect's aquatic young catch prey by shooting out an extensible lower lip armed with hooks and spines?

Dragonfly young keep the lip folded under the body, then fire it out at great speed using pressure from the abdominal muscles.

In a honeybee colony, which stingless male bees develop from eggs that have been left unfertilised?

Drones therefore have a mother but no father, while a fertilised larva becomes a queen only if it is fed solely on royal jelly.

Which insect undergoes incomplete metamorphosis, growing wing-buds through several stages with no pupal stage at all?

Grasshopper hatchlings already look like miniature adults and simply grow more like them at each stage, the wing-buds enlarging every time.

The axolotl, a zoo and aquarium favourite that never outgrows its larval form, is which kind of animal?

Salamander species normally transform for life on land, but the axolotl breeds while still a water-dwelling juvenile, a trait known as neoteny.

What is the botanical name for a 'seed leaf', the first leaf to appear from a sprouting seed?

Cotyledon number is how botanists sort the flowering plants into two great groups: monocots have one and dicots have two.

Which organs, which disappear as the lungs develop, allow a newly hatched frog to breathe underwater?

Gills begin on the outside of the body and are soon covered over by skin, before disappearing altogether as the front legs emerge.

European eels leave their rivers and cross the ocean to spawn in which sea of the North Atlantic?

Sargasso Sea waters were named the likely spawning ground by Danish researcher Johannes Schmidt in the early 1900s, and a later breeding project used a swimming machine to mimic the journey.

In American alligators, which condition inside the nest decides whether an egg hatches as a male or a female?

Temperature between about 32.5 and 33.5 °C produces males, while nests below 31.5 °C or above 34.5 °C produce females.

What is the name for the temporary sharp projection on a chick's bill, used to break out of the shell?

Egg tooth use is brief: after hatching it falls off or is absorbed into the growing bill, and baby crocodiles carry one on the snout for the same job.

Which bird lays its eggs in the nests of smaller species such as reed warblers, leaving them to raise its chick?

Cuckoo eggs are larger than those of the foster parents, yet in each type of host nest they resemble the host's own eggs.

What is the name for a young kangaroo, which is about the size of a lima bean when it is born?

Joey development is finished outside the womb: the tiny newborn climbs into the mother's pouch and usually stays there for about nine months.

Which animal has the longest pregnancy of any mammal, carrying its calf for around 22 months?

Elephant pregnancies run so long that the foetus gets extra time to develop, particularly its brain and trunk.

What is the term for the period a mammal's young spends developing inside the womb, about nine months in humans?

Gestation in humans is divided into three trimesters of roughly three months each, and labour that starts before 37 weeks counts as preterm.

Which temporary organ, joined to an unborn baby by the umbilical cord, attaches to the wall of the mother's womb?

Placenta tissue grows fast and lives briefly: it is shed after the birth, and in humans the cord tying it to the baby is about 55 to 60 cm long.

What is the name for the first cell of a new organism, formed when a sperm fuses with an egg?

Zygote DNA combines the genetic material of both parents, so this one cell holds all the instructions for a new individual.

What is the name for the process in which a seed takes up water, splits its coat, and begins to sprout?

Germination starts at the bottom: the first part of the plant to emerge from the seed is the embryonic root, known as the radicle.

What is the name for the transfer of grains from a flower's anther to a stigma, often carried out by bees?

Pollination is not only the work of insects: birds and bats do it too, and wind handles about 98% of the cases where no animal is involved.

Carrots and parsley flower only in their second growing season and then die, which makes them what type of plant?

Biennial crops grown for their roots or leaves are harvested after the first year, before they ever get the chance to flower and set seed.

Ferns have neither flowers nor seeds, so what do they release in order to reproduce?

Spores grow first into a short-lived plantlet called a prothallus, which makes the egg and sperm cells that produce the next leafy fern.

In flowering plants, which part of the flower typically swells and ripens into the fruit that surrounds the seeds?

Ovary walls ripen into the flesh of an orange, a tomato or a pumpkin, all of which count as fruits to a botanist.

Which tropical plant's fruit has a thick fibrous husk that keeps it afloat, letting ocean currents spread its seed?

Coconut fruits of the wild type are angular and ridged to float better, yet drift models suggest they could not have crossed the Pacific without human help.

Which marine reptiles are thought to use Earth's magnetic field to find their way back to their home beaches to nest?

Sea turtles in the most extreme cases return to lay their eggs on the very beach where they themselves hatched.