Every fact in the three insect lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the facts are simplified or less certain: sources give different numbers of described insect species: about 900,000 according to the Smithsonian [1][2] and more than one million according to the Royal Entomological Society [6]; the total including undescribed species is unknown, with estimates from about 2 million to 30 million more [2]. The figure of 10 quintillion living insects is an estimate [2]. 'Three body parts and six legs' is true of adult insects; larvae such as caterpillars can look very different, and some insects have no wings [1][4]. The German study of flying insects (a fall of over 75% in 27 years) is one study in one country [8].
All sources
[1] What is an insect?
Smithsonian National Museum of Natural History · Reliability: High
Type: National natural history museum (teaching resource)
All insects have three main body parts (head, thorax and abdomen), six legs and a pair of antennae to sense things, and zero or two pairs of wings. Insects are arthropods: animals with an exoskeleton (a hard outer covering) and jointed legs. A spider, with eight legs, is not an insect. Ants and fleas are examples of insects without wings; beetles have hard wing cases (elytra) protecting the wings; flies have modified wings called halteres that help balance and steering. There are about 900,000 species of insects, around 10 quintillion individual insects, four out of every five animals is an insect, and insects have existed for over 400 million years.
Smithsonian Institution (Encyclopedia Smithsonian) · Reliability: High
Type: National museum (information sheet)
Some 900 thousand kinds of living insects are known. Undescribed species are estimated at 2 million (conservative) to 30 million. At any time an estimated 10 quintillion (10,000,000,000,000,000,000) individual insects are alive. Insects probably have the largest biomass of the land animals.
Museum of the Earth (Paleontological Research Institution, Ithaca) · Reliability: High
Type: Natural history museum
The head holds most of the sense organs, including the mouth, antennae and eyes; the thorax is the central body region; the abdomen is the last and largest. Antennae are used to taste and smell. Compound eyes are made of many tiny lenses; the more lenses, the sharper the vision. Most insects breathe through small holes on the sides of the body called spiracles. Insects have six segmented legs; most have four wings, but some have none.
Amateur Entomologists' Society · Reliability: Medium-high
Type: Entomological society (education fact file)
The exoskeleton cannot expand with growth, so it must be shed and a new one formed; moulting is called ecdysis and the stage between moults an instar. Complete metamorphosis: egg, larva, pupa, adult (butterflies, moths, bees, wasps, true flies, beetles). Incomplete metamorphosis: egg, nymph, adult (dragonflies, grasshoppers, earwigs, cockroaches, true bugs).
Arthropods have a sturdy chitinous exoskeleton and jointed appendages and periodically moult. Hexapods (insects) have six legs (three pairs) and three tagmata: head, thorax and abdomen, with one pair of antennae and a pair of compound eyes. Tracheae open to the surface through spiracles, and these fine tubes exchange gases directly between the air and the cells. Insects excrete with Malpighian tubules. Insects are the largest clade of arthropods in species diversity; an estimated 85% of all known species are arthropods. Chelicerates (such as spiders) have two body regions and no antennae; myriapods have from 10 to 750 legs.
More than one million insect species have been described, over half of all described living species; insects are the most abundant group of animals and live on all seven continents. About 84% of crops grown in Europe rely on pollinators such as bees, flies, wasps, beetles, butterflies and moths. Ladybirds control aphids. Insects are a major food for many birds, fish and mammals. Many insects break down dead and decaying material, helping to build fertile soil. Insects also transmit some serious diseases of people, animals and plants.
Natural History Museum, London · Reliability: High
Type: Natural history museum
Sink a clean yoghurt pot into flat ground near vegetation with its rim level with the soil; put some leaves inside so animals can hide; protect it from rain with a small roof on stones and do not place it where water runs in. Leave it overnight and check it in the morning before it gets warm; if set during the day, check at least every few hours. Tip the catch into a tray, record it and release the animals in a sheltered place. Catches include beetles, woodlice, millipedes, centipedes, earwigs, springtails and spiders. Woodlice have seven pairs of legs; pill millipedes have two pairs of legs per segment.
Used in: Ages 10–11 (experiment); Ages 15–16 (experiment)
[8] Speaking up for the little ones: why bugs need our help more than ever
Natural History Museum, London · Reliability: Medium-high
Type: Natural history museum (news article)
Without insects many plants would go unpollinated; insects help recycle nutrients and are food for birds. Insect traps in Germany recorded a fall of over 75% in flying insects over 27 years. Climate change and agriculture are given as causes of insect declines; pesticides, outdoor lighting and loss of habitat also harm insects.