The definition of the Palaearctic part of the Holarctic region follows Beaman (1994):
- Iceland and Macaronesia are included. In Mauritania, the islands of the Banc d’Arguin, and the Cap Blanc peninsula are included, and then the boundary follows the 21°N line across Africa from the Atlantic to the Red Sea coast (but locally extending southwards to include all of Libya, and Chad north of 19°N). The whole of the Arabian peninsula is included. In southern Asia the boundary runs from the Makran coast of Pakistan at Ras Ormara northwards to the Harboi Hills and the mountains of Quetta, and along the Sulaiman Range. The line then runs along the mountainous borderlands of Pakistan and Afghanistan, the main range of the Himalayas, the mountains at the extreme northernmost tip of Myanmar, the Lijiang Range in northern Yunnan and the mountainous western margins of the Red Basin of Sichuan [species included are limited to those known to occur at or above: 2000m in northwestern Pakistan and adjacent Afghanistan, the northwestern Himalayas (Pakistan/Kashmir) and central/northern Sichuan; 2500m in the western Himalayas (Himachal Pradesh), northern Yunnan and southern Sichuan; and 2800m in the eastern Himalayas (Nepal to Arunachal Pradesh) and northernmost Myanmar]. In eastern China, the boundary follows the Yangtze/Huang Ho watershed in southern Gansu, the Qinlang Shan in Shaanxi, and then the 34°N line to the Yellow Sea coast. On the Pacific fringe, the Nansei, Daito, Kazan and Ogasawara Islands are included.
- [For the purposes of this checklist, the Socotra archipelago is additionally included within the Palaearctic. It is part of the Middle East, as defined by Porter & Aspinall (2010) and by OSME ('the OSME region'), and politically (as part of the Republic of Yemen). However those species restricted to the Socotra archipelago are clearly indicated.]
The definition of the Nearctic part follows Voous (1977):
- Greenland, Canada, St.-Pierre-et-Miquelon, the Continental US (Alaska and the Lower 48), the non-tropical states of Mexico (Baja California, Baja California Sur, Sonora, Chihuahua, Durango, Zacatecas, Aguascalientes, Guanajuato, Querétaro, México, Distrito Federal, Coahuila and Nuevo León), the Bahamas, and Bermuda.
The Atlantic and Pacific Oceans north of the Tropic of Cancer (except for the Hawaiian Ridge area) are included within the Holarctic region.