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Sources

Where the facts come from

Every factual claim on this site links to its source. This is the full list, and every place where the sources disagree.

How we checked

Each fact was written alongside its source. Our build script stores the source text and, for every fact, checks that the key words and figures really appear in it. 161 of 161 checks passed when this site was last built. All sources were read on 30 Oct 2026. Facts that can change (species counts, trends and records) carry “checked 30 Oct 2026” next to their source link.

Main sources: Butterfly Conservation, the Natural History Museum, London, the American Museum of Natural History, the Australian Museum, the Oxford University Museum of Natural History, Manx Wildlife Trust, the US Forest Service, the US National Park Service, the University of York, Utrecht University, Kew Gardens, a peer-reviewed paper in Proceedings of the Royal Society B, Britannica (its main article text only) and Merriam-Webster.

When sources disagree

Where trusted sources give different figures, we don’t pick one: we show them all, each with its source.

How many kinds of butterflies and moths are there?

Two trusted museums and reference works give different world totals. New species are still being found and named, so treat both as round figures.

How far do monarchs fly?

One figure is the usual journey from Canada to Mexico; the other is the farthest some monarchs fly. Both come from trusted sources, so we show both.

Do Painted Ladies fly back south?

Britannica’s article describes one-way emigrations. The 2009 radar study led by the University of York found Painted Ladies flying back south in autumn, high up and out of sight of people on the ground.

Is the Large Tortoiseshell back in Britain?

Both statements come from Butterfly Conservation. The butterfly has been declared resident again, but the official GB Red List has not yet been updated.

How many moth species does Britain have?

Butterfly Conservation says over 2,500 moths. The Oxford museum’s UK figure of 2,495 is for butterflies and moths together. The sources don’t explain the gap.

All sources (45)