The Insect Limestone has long been known as a source of exquisitely preserved insects and other arthropods. It occurs on the north side of the Isle of Wight and is latest Eocene in age. A summary of the history of the study of the Insect Limestone is given, along with detailed stratigraphical and sedimentological information. This paper is the first in a thematic set of papers.

Latest Eocene fossil plant remains occur in concentrations within blue-grey micrite known as Insect Limestone near the base of the Bembridge Marls Member (Bouldnor Formation, Solent Group), Isle of Wight, southern England. Some of the previously reported taxa (collections in the Natural History Museum, London) are not preserved within the Insect Limestone. These (e.g., all Arecaceae (palms)) are excluded from the floral list. New non-destructive techniques have yielded additional taxonomic information. Leaves previously assigned to Ficus and Fagus are now incertae sedis. Wetland elements are abundant, particularly Typha, but also Acrostichum, Azolla, Potamogeton, Sparganium and others. Non-wetland elements are rare. Trees and shrubs included representatives of Betulaceae, Caprifoliaceae, Juglandaceae, Lauraceae, Rhamnaceae (the sclerophyllous Zizyphus), other flowering plants and several genera of conifers. There are rare specimens of possible herbaceous plants and propagules with plumes or awns, the latter possibly an early fossil record of Clematis. The common plant remains were probably derived from vegetation near a freshwater body, sometimes with slight brackish influence, whilst rarer elements were probably blown in from a greater distance. There is little evidence of plant–insect interaction; one leaf with small galls, a stem containing an insect larva and a possible association between stratiomyid flies and Typha.

Molluscs from the Insect Limestone of the Bembridge Marls Member are described. The gastropods Lymnaea (Galba) longiscata (Brongniart 1810), Planorbarius discus (Edwards 1852), Gyraulus similis Férussac, 1814, Hippeutis headonensis Jodot, 1942, Viviparus lentus (Solander 1766) and Viviparus angulosus (J. Sowerby 1817) indicate freshwater alkaline conditions. The cerithioid gastropod Tarebia acuta (J. Sowerby 1822) probably represent more brackish conditions. Polymesoda (Pseudocyrena) obovata (J. Sowerby 1817) is the only bivalve present. All were potentially washed into the depocentre. Despite a wide outcrop of the Insect Limestone on the Isle of Wight's northwest and northeast coasts, there are no records of molluscs other than from the Gurnard/Thorness Bay area on the northwest coast of the island.

The arachnids from the late Eocene Insect Limestone of the Isle of Wight are reviewed. Only spiders (Araneae) have been recorded, of which several dozen are known, mostly juveniles. Nearly all are araneomorphs; the putative mygalomorph Eoatypus woodwardii McCook, 1888 was removed from that infraorder by Selden (2001), but new specimens, yet to be described, could belong in this group. Among the adult specimens, which are thus identifiable to family level, most belong to the argyronetid water-spider Vectaraneus yulei Selden, 2001; some resemble araneids, and a small number can be referred to other families. New morphological information on the holotype of Vectaraneus is presented, and three other specimens are described in more detail here, in Segestriidae, Araneidae and Salticidae. Segestriids are nocturnal sedentary hunters living in tubular retreats in rock or bark crevices. Araneids are the archetypal weavers of orb webs. Salticids are the familiar jumping spiders; the one described here is an ant mimic. Their presence suggests a drier habitat was present somewhere in the source environment for the fossil biota, and they were probably inhabitants of the raised hammocks suggested for the Insect Bed palaeoenvironment.

The odonatan fauna of the Late Eocene of the Isle of Wight is revised. The following taxa are revised or described: the gomphaeschnids Oligoaeschna? anglica Cockerell & Andrews, 1916 and Anglogomphaeschna eocenica gen. et sp. nov.; the aeshnids ‘Oplonaeschna’ vectensis Cockerell & Andrews, 1916, Aeschnophlebia andreasi Nel et al., 2005, Oligaeschna wedmanni sp. nov., and a ‘Gynacanthinae’ species; Neophya legrandi sp. nov., first fossil representative of the Cordulephyidae; three undescribed ‘Corduliidae’; Eomacrodiplax incompleta gen. et sp. nov., first fossil representative of the Urothemistidae; the second representative of the Palaeogene family Bolcathoridae; a Thaumatoneuridae Dysagrionini species A; the megapodagrionid Oligoargiolestes oligocenum Kennedy, 1925; the two hypolestids Anglohypolestes fasciata gen. et sp. nov. and Eohypolestes hooleyi gen. et sp. nov.; the coenagrionid ‘Enallagma' oligocena Cockerell & Andrews, 1916, and three other undescribed species; Angloprotoneura emilielacroixi gen. et sp. nov., first fossil European representative of the damselfly family Protoneuridae; and the lestid Lestes aff. regina Théobald, 1937. This fauna has strong similarities with the Recent Afrotropical and Indo-Malayan Odonata, suggesting a warm palaeoclimate for the Late Eocene of the Isle of Wight. ‘Megalestes’ anglicus Cockerell, 1915 is a Zygoptera Lestiformia or Coenagrionomorpha of uncertain affinities.

Late Eocene fossil Psocodea from the Isle of Wight are studied and classified within three new genera and seven species (Wightipsocus acourti (Cockerell 1921) gen. nov. et n. comb., Wightipsocus intasi gen. et sp. nov., Wightipsocus rossi gen et sp. nov., Awightipsocus jarzembowskii gen. et sp. nov., Awightipsocus megaloi gen. et sp. nov. Awightipsocus minimus gen. et sp. nov. and Wightimicropsocus inexpectatus gen. et sp. nov.) without however attributing them to any family. A key for fossil Psocodea from the Isle of Wight is given.

Thirty-two thrips fossils were studied from the Bembridge Marls, late Eocene of the Isle of Wight, S. England. Two extant families are recorded, Aeolothripidae with two species and Thripidae with three species. Described as new are Sinaeolothrips Shmakov gen. n. (Aeolothrips brodiei Cockerell, 1917, type species), Aeolothrips jarzembowskii Shmakov sp. nov (Aeolothripidae) and Coccothrips hoffeinsorum Shmakov, sp.nov.(Thripidae: Panchaetothripinae). The genus Thrips is tentatively recorded as fossil for the first time. Taxonomic composition of thrips is close to the Recent ones.

The trichopteran assemblage of the Late Eocene Bembridge Marls is revised. six species in five genera and four families are identified, with four species and two genera described as new: (Beraeidae: Beraeodes vectensis Cockerell, 1921 and B. anglicus Cockerell, 1921; Phryganeidae: Bembridgea insularia gen. sp. nov.; Polycentropodidae: ?Plectrocnemia incompleta Sukatsheva, sp. nov.; Philopotamidae: Wormaldia longaeva Sukatsheva, sp. nov.; incertae familiae: Paleodicella anomala Sukatsheva, gen. sp. nov.). The assemblage is unique in being absolutely dominated by the generally uncommon family Beraeidae, and particularly by the single species Beraeodes vectensis. Except for a representative of ubiquitous Phryganaeidae, all the caddis-flies recorded apparently had oxy- and psychrophilous larvae confined to springs and cold streams (or else mosses near water), thus indicating the absence of fresh lakes or slow running waters near the depositional water body.

The types and undescribed material of the hymenopteran fossils of the Insect Bed of the Bembridge Marls from the Isle of Wight (UK) are critically revised and studied. A total of 1460 fossils are recorded and attributed to 20 families: Gasteruptiidae s.l. (1); Proctotrupidae (3); Diapriidae (24); Cynipidae (7); Figitidae (6); Pteromalidae (1); Agaonidae (3); Scelionidae (12); Platygastridae (2); Ichneumonidae (32); Braconidae (75); Bethylidae (3); Crabronidae (2); Sphecidae (1); Apidae (2); Scoliidae (1); Tiphiidae (2); Vespidae (4); and Formicidae (1220). Described as new are 51 species, 13 genera, two tribes and two subfamilies. Minimum number of species recorded (either as described species or representing higher taxa with no described species in the assemblage) is 118. The composition of the hymenopteran assemblage is most similar to that of Baltic amber and indicative of a well forested territory, as well as of a humid, equable (aseasonal but not very hot) climate, more typically equable than in the Baltic amber source area, judging from the absence of Aphidiinae and scarcity of aphids.