Eight hundred and eighteen of the 873 painted lady butterflies recorded in three springs of transect counting at Gibraltar turned up in a single year. That is 94 per cent of a three year total landing in 2006 alone. Before you plan anything around this migration, that one ratio tells you most of what you need to know. The painted lady does not arrive on a timetable. It arrives in pulses. In a quiet year you can stand in the right place, in the right week, on a perfect morning, and see almost nothing. The only butterfly count from Gibraltar dense enough to argue with is [a three year transect study at Windmill Hill Flats](https://www.eje.cz/artkey/eje-201404-0013_Species_composition_and_dynamics_in_abundance_of_migrant_and_sedentary_butterflies_Lepidoptera_at_Gibraltar_d.php), published in the European Journal of Entomology in 2014 by Keith Bensusan and Charles Perez of the Gibraltar Ornithological and Natural History Society with British and Polish co-authors. The method was plain. Line transects of 130 metres, two of them in 2006 and 2007 and one in 2008, walked every day from 25 April to 5 June, three times a day at roughly 10am, 1pm and 4pm, recording every butterfly within 3 metres of either side. That came to 414 separate transect surveys. The result was 2,508 butterflies of 19 species. The painted lady was the most numerous single species at 873 individuals, 34.8 per cent of everything counted. Together with the clouded yellow and the red admiral, the three migratory species accounted for around 70 per cent of every butterfly seen. All the resident species combined made up the remaining 30 per cent. |Species|Individuals|Share of all butterflies|Surveys it appeared in| |Painted lady|873|34.8%|34.5%| |Clouded yellow|692|27.6%|50.7%| |Common blue|450|17.9%|28.5%| |Red admiral|184|7.3%|19.1%| |Small white|69|2.8%|12.8%| |Swallowtail|66|2.6%|11.4%| |Green striped white|50|2.0%|7.7%| |All 19 species|2,508|100%|414 surveys| Read the last column, because it is the one that changes how you plan. The painted lady was the most abundant butterfly on the site and yet it showed up in only 34.5 per cent of surveys, while the clouded yellow, with 181 fewer individuals, appeared in 50.7 per cent of them. The painted lady averaged 2.11 butterflies per survey with a standard deviation of 7.78. A number scattered that badly is not a trickle. It is mostly nothing, interrupted by a great deal at once. The counts also hand you a date. Painted lady, clouded yellow and red admiral all peaked between Julian days 130 and 140, which is 10 to 20 May. The median date for the painted lady was day 135, which is 15 May. If you get one week in Gibraltar for this, that is the week. For scale, GONHS lists [609 species of Lepidoptera recorded in Gibraltar](https://www.gonhs.org/wildlife/fauna/lepidoptera) up to 30 October 2020, the great majority of them moths. Gibraltar's butterfly fauna at the time of the study stood at 32 species, and 22 of those had been recorded regularly at this one patch of 12 hectares. No individual painted lady completes the circuit. The species runs it as a relay, and the butterfly returning to a place is several generations removed from the one that left it. The distances have kept growing as the fieldwork has pushed further south. Hydrogen isotope work [published in 2018](https://www.sciencedaily.com/releases/2018/06/180613102004.htm) showed sub Saharan origins for migrants collected around the Mediterranean in February, evidence of a northward trans Saharan spring leg, and put the annual circuit at 12,000 km with two Sahara crossings. A 2021 analysis called it [the longest annual insect migration circuit known](https://pmc.ncbi.nlm.nih.gov/articles/PMC8256005/) at 12,000 to 14,000 km. Then came seven field expeditions across six African countries in the Decembers and Januarys between 2017 and 2020, whose authors write that their results [expand the Palearctic African migratory annual cycle up to 15,000 km](https://pmc.ncbi.nlm.nih.gov/articles/PMC10120051/). We are quoting that last one rather than paraphrasing it, because the wording is ambiguous about whether 15,000 km is the new total or the size of the extension, and we would rather hand you the sentence than guess at it. What is not in doubt is the direction of travel. You will still see 12,000 km quoted almost everywhere, including in headlines written this year. That was the 2018 figure, and every study since has made the circuit longer. A 2024 isotope study of 118 specimens collected either side of the Sahara [describes the annual cycle as 8 to 10 overlapping generations](https://pmc.ncbi.nlm.nih.gov/articles/PMC11626715/) of continuous movement and breeding. Autumn legs exceeded 3,000 km, some of them 3,500 km from northern Europe to West Africa. A generation takes roughly a month in the warmth of the Afrotropics and an adult lives a few weeks, so the butterfly leaving the Sahel in February is four or five generations removed from the one that left