Species Recorded | Taxon | Scientific Name | Common Name | Records | Latest |
| amphibian | Ichthyosaura alpestris | Alpine Newt | 2 | 2010 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon | an Ichneumon species (unidentified) | 45 | 2025 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon confusor | an ichneumon wasp | 1 | 2020 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon gracilicornis | an ichneumon wasp | 1 | 2003 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumonidae | an Ichneumonidae species (unidentified) | 12 | 2023 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon lugens | an ichneumon wasp | 1 | 2022 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon sarcitorius | an ichneumon wasp | 10 | 2023 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon stramentarius | an ichneumon wasp | 3 | 2019 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon stramentor | an insect - hymenopteran | 2 | 2007 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ichneumon suspiciosus | an ichneumon wasp | 2 | 2006 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ischnus | an Ischnus species (unidentified) | 1 | 2015 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Ischnus inquisitorius | an Ischnus species | 1 | 2021 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Itoplectis alternans | an ichneumon wasp | 3 | 2003 |
| ant, bee, wasp, sawfly or ichneumon (and others) | Itoplectis maculator | an ichneumon wasp | 2 | 1997 |
| beetle | Ilybius | an Ilybius species (unidentified) | 3 | 2011 |
| beetle | Ilybius ater | a water beetle | 64 | 2021 |
| beetle | Ilybius chalconatus | a water beetle | 15 | 2011 |
| beetle | Ilybius fenestratus | a water beetle | 1 | 1999 |
| beetle | Ilybius fuliginosus | a water beetle | 18 | 2023 |
| beetle | Ilybius guttiger | a water beetle | 2 | 2012 |
| beetle | Ilybius montanus | a water beetle | 1 | 1999 |
| beetle | Ilybius quadriguttatus | a water beetle | 86 | 2013 |
| beetle | Ischnodes sanguinicollis | a click beetle | 1 | 1979 |
| beetle | Ischnomera | an Ischnomera species (unidentified) | 2 | 2013 |
| beetle | Ischnomera cyanea | a thick-legged flower beetle | 25 | 2024 |
| beetle | Ischnomera sanguinicollis | a thick-legged flower beetle | 7 | 2021 |
| beetle | Ischnopterapion | an Ischnopterapion species (unidentified) | 1 | 2021 |
| beetle | Ischnopterapion loti | a seed weevil | 31 | 2017 |
| beetle | Ischnopterapion modestum | a seed weevil | 1 | 1999 |
| beetle | Ischnopterapion virens | a seed weevil | 26 | 2019 |
| beetle | Ischnosoma splendidum | an insect - beetle (Coleoptera) | 2 | 2020 |
| beetle | Isochnus foliorum | a weevil | 2 | 1985 |
| beetle | Isomira murina | a darkling beetle | 17 | 2023 |
| bird | Ichthyaetus melanocephalus | Mediterranean Gull | 2997 | 2022 |
| bird | Ixobrychus minutus | Little Bittern | 4 | 2020 |
| bug | Iassus lanio | a leafhopper | 20 | 2023 |
| bug | Idiocerus | an Idiocerus species (unidentified) | 3 | 2018 |
| bug | Idiocerus herrichi | a leafhopper | 7 | 2022 |
| bug | Idiocerus lituratus | a leafhopper | 4 | 2022 |
| bug | Idiocerus stigmaticalis | a leafhopper | 5 | 2023 |
| bug | Ilyocoris cimicoides | Saucer bug | 165 | 2023 |
| bug | Ischnodemus sabuleti | a ground bug | 22 | 2022 |
| bug | Issus coleoptratus | a beetle bug | 69 | 2025 |
| caddis fly | Ithytrichia | an Ithytrichia species (unidentified) | 1 | 1997 |
| crustacean | Idotea granulosa | a crustacean | 2 | 1940 |
| dragonfly, hawker or damselfly | Ischnura | an Ischnura species (unidentified) | 1 | 2011 |
| dragonfly, hawker or damselfly | Ischnura elegans | Blue-tailed Damselfly | 2906 | 2025 |
| dragonfly, hawker or damselfly | Ischnura pumilio | Scarce Blue-tailed Damselfly | 34 | 2023 |
| fungus | Inocybaceae | an Inocybaceae agaric (unidentified) | 1 | 2023 |
| fungus | Inocybe | a Inocybe agaric (unidentified) | 17 | 2002 |
| fungus | Inocybe abjecta | an agaric | 1 | 1998 |
| fungus | Inocybe acuta | an agaric | 1 | 2001 |
| fungus | Inocybe adaequata | an agaric | 19 | 2013 |
| fungus | Inocybe albomarginata | an agaric | 2 | 2002 |
| fungus | Inocybe assimilata | an agaric | 3 | 2000 |
| fungus | Inocybe asterospora | an agaric | 47 | 2021 |
| fungus | Inocybe auricoma | an agaric | 2 | 2008 |
| fungus | Inocybe bongardii | an agaric | 5 | 2010 |
| fungus | Inocybe calamistrata | an agaric | 2 | 1998 |
| fungus | Inocybe calospora | an agaric | 6 | 2010 |
| fungus | Inocybe cervicolor | an agaric | 2 | 2008 |
| fungus | Inocybe cincinnata | an agaric | 6 | 2007 |
| fungus | Inocybe cincinnata var. cincinnata | an agaric | 11 | 2012 |
| fungus | Inocybe cincinnata var. major | an agaric | 11 | 2011 |
| fungus | Inocybe cookei | an agaric | 13 | 2013 |
| fungus | Inocybe corydalina | an agaric | 1 | 2000 |
| fungus | Inocybe curvipes | an agaric | 5 | 2009 |
| fungus | Inocybe descissa | an agaric | 1 | 2000 |
| fungus | Inocybe dulcamara | an agaric | 3 | 2008 |
| fungus | Inocybe duriuscula | an agaric | 5 | 2014 |
| fungus | Inocybe erubescens | Red-staining Inocybe | 8 | 2013 |
| fungus | Inocybe eutheles | an agaric | 2 | 1996 |
| fungus | Inocybe fibrosoides | an agaric | 3 | 2006 |
| fungus | Inocybe flavella | an agaric | 3 | 2008 |
| fungus | Inocybe flocculosa | an agaric | 49 | 2009 |
| fungus | Inocybe fraudans | an agaric | 16 | 2010 |
| fungus | Inocybe fuscidula | an agaric | 5 | 2021 |
| fungus | Inocybe fuscidula var. fuscidula | an agaric | 14 | 2014 |
| fungus | Inocybe geophylla | an agaric | 50 | 2023 |
| fungus | Inocybe geophylla var. geophylla | an agaric | 76 | 2014 |
| fungus | Inocybe geophylla var. lilacina | an agaric | 91 | 2023 |
| fungus | Inocybe glabripes | an agaric | 1 | 2008 |
| fungus | Inocybe godeyi | an agaric | 8 | 2011 |
| fungus | Inocybe griseolilacina | an agaric | 11 | 2010 |
| fungus | Inocybe haemacta | an agaric | 7 | 2006 |
| fungus | Inocybe hirtella var. bispora | an agaric | 2 | 2008 |
| fungus | Inocybe hirtella var. hirtella | an agaric | 3 | 1998 |
| fungus | Inocybe hystrix | an agaric | 6 | 1994 |
| fungus | Inocybe lacera var. lacera | an agaric | 2 | 1993 |
| fungus | Inocybe maculata | an agaric | 36 | 2012 |
| fungus | Inocybe margaritispora | an agaric | 13 | 2010 |
| fungus | Inocybe mixtilis | an agaric | 28 | 2014 |
| fungus | Inocybe napipes | Bulbous Fibrecap | 7 | 2014 |
| fungus | Inocybe nitidiuscula | an agaric | 29 | 2010 |
| fungus | Inocybe oblectabilis | an agaric | 5 | 2004 |
| fungus | Inocybe obscura | an agaric | 3 | 2003 |
| fungus | Inocybe obscurobadia | an agaric | 1 | 2008 |
| fungus | Inocybe obsoleta | an agaric | 1 | 2014 |
| fungus | Inocybe paludinella | an agaric | 1 | 1999 |
| fungus | Inocybe phaeodisca | an agaric | 2 | 2014 |
| fungus | Inocybe phaeodisca var. geophylloides | an agaric | 6 | 2014 |
| fungus | Inocybe phaeodisca var. phaeodisca | an agaric | 5 | 2009 |
| fungus | Inocybe phaeoleuca | an agaric | 27 | 2012 |
| fungus | Inocybe posterula | an agaric | 1 | 2003 |
| fungus | Inocybe praetervisa | an agaric | 31 | 2010 |
| fungus | Inocybe pseudoreducta | an agaric | 1 | 2010 |
| fungus | Inocybe pusio | an agaric | 16 | 2021 |
| fungus | Inocybe putilla | an agaric | 1 | 2014 |
| fungus | Inocybe pyriodora | an agaric | 28 | 2001 |
| fungus | Inocybe quietiodor | an agaric | 2 | 2006 |
| fungus | Inocybe rimosa | Split Fibrecap | 102 | 2013 |
| fungus | Inocybe salicis | an agaric | 1 | 2009 |
| fungus | Inocybe sindonia | an agaric | 27 | 2021 |
| fungus | Inocybe soluta | an agaric | 1 | 2008 |
| fungus | Inocybe splendens | an agaric | 18 | 2013 |
| fungus | Inocybe squamata | an agaric | 9 | 2007 |
| fungus | Inocybe stellatospora | Woolly Fibrecap | 2 | 2013 |
| fungus | Inocybe subcarpta | an agaric | 1 | 1990 |
| fungus | Inocybe tabacina | an agaric | 2 | 1997 |
| fungus | Inocybe tenebrosa | an agaric | 1 | 1994 |
| fungus | Inocybe tigrina | an agaric | 1 | 1995 |
| fungus | Inocybe trechispora | an agaric | 1 | 1999 |
| fungus | Inocybe whitei | an agaric | 1 | 2008 |
| fungus | Inocybe xanthomelas | an agaric | 10 | 2014 |
| fungus | Inonotus hispidus | a basidiomycete fungus | 22 | 2021 |
| fungus | Ischnoderma benzoinum | a basidiomycete fungus | 2 | 2010 |
| lichen | Illosporiopsis christiansenii | a lichen | 3 | 2020 |
| lichen | Inoderma subabietinum | a lichen | 1 | 2013 |
| moss | Isothecium | a mouse-tail moss (unidentified) | 1 | 2012 |
| moss | Isothecium alopecuroides | Larger Mouse-tail Moss | 34 | 2023 |
| moss | Isothecium myosuroides | Slender Mouse-tail Moss | 57 | 2023 |
| moss | Isothecium myosuroides var. myosuroides | a slender mouse-tail moss | 6 | 2003 |
| moth or butterfly - butterfly | Issoria lathonia | Queen of Spain Fritillary | 1 | 1994 |
| moth or butterfly - macro moth | Idaea | an Idaea species (unidentified) | 1 | 2013 |
| moth or butterfly - macro moth | Idaea aversata | Riband Wave | 4622 | 2025 |
| moth or butterfly - macro moth | Idaea aversata ab. remutata | Riband Wave (unbanded form) | 106 | 2023 |
| moth or butterfly - macro moth | Idaea biselata | Small Fan-footed Wave | 1379 | 2025 |
| moth or butterfly - macro moth | Idaea degeneraria | Portland Ribbon Wave | 1 | 2011 |
| moth or butterfly - macro moth | Idaea dilutaria | Silky Wave | 283 | 2024 |
| moth or butterfly - macro moth | Idaea dimidiata | Single-dotted Wave | 1418 | 2024 |
| moth or butterfly - macro moth | Idaea emarginata | Small Scallop | 49 | 2023 |
| moth or butterfly - macro moth | Idaea fuscovenosa | Dwarf Cream Wave | 74 | 2021 |
| moth or butterfly - macro moth | Idaea rusticata | Least Carpet | 18 | 2025 |
| moth or butterfly - macro moth | Idaea seriata | Small Dusty Wave | 1322 | 2025 |
| moth or butterfly - macro moth | Idaea straminata | Plain Wave | 22 | 2020 |
| moth or butterfly - macro moth | Idaea subsericeata | Satin Wave | 23 | 2017 |
| moth or butterfly - macro moth | Idaea trigeminata | Treble Brown Spot | 402 | 2024 |
| moth or butterfly - macro moth | Ipimorpha retusa | Double Kidney | 12 | 2014 |
| moth or butterfly - macro moth | Ipimorpha subtusa | Olive (moth) | 64 | 2023 |
| moth or butterfly - micro moth | Incurvaria masculella | a longhorn moth | 71 | 2024 |
| moth or butterfly - micro moth | Incurvaria oehlmanniella | a longhorn moth | 14 | 2016 |
| moth or butterfly - micro moth | Incurvaria pectinea | a longhorn moth | 2 | 1990 |
| moth or butterfly - micro moth | Incurvaria praelatella | a longhorn moth | 10 | 2018 |
| moth or butterfly - micro moth | Infurcitinea argentimaculella | a micro-moth | 8 | 2023 |
| moth or butterfly - micro moth | Isotrias rectifasciana | a tortrix moth | 7 | 2021 |
| moth or butterfly - moth (macro or micro not listed) moth | Incurvariidae | an Incurvariidae species (unidentified) | 1 | 2011 |
| plant | Iberis amara | Wild Candytuft | 4 | 1989 |
| plant | Iberis sempervirens | Perennial Candytuft | 13 | 2023 |
| plant | Iberis umbellata | Garden Candytuft | 16 | 2016 |
| plant | Ilex | a holly (unidentified) | 10 | 2024 |
| plant | Ilex aquifolium | Holly | 6366 | 2025 |
| plant | Ilex aquifolium x perado = I. x altaclerensis | Highclere Holly | 6 | 2019 |
| plant | Ilex cornuta | a flowering plant | 1 | 2000 |
| plant | Impatiens | an Impatiens species (unidentified) | 2 | 2013 |
| plant | Impatiens balfourii | a balsam | 1 | 1993 |
| plant | Impatiens capensis | Orange Balsam | 12 | 2019 |
| plant | Impatiens glandulifera | Himalayan Balsam | 1630 | 2024 |
| plant | Impatiens parviflora | Small Balsam | 26 | 2019 |
| plant | Inula conyzae | Ploughman's-spikenard | 587 | 2023 |
| plant | Inula crithmoides | Golden-samphire | 20 | 2009 |
| plant | Inula helenium | Elecampane | 37 | 2019 |
| plant | Ipomoea purpurea | Common Morning-glory | 1 | 1928 |
| plant | Ipomoea tricolor | a flowering plant | 1 | 2014 |
| plant | Iris | an iris (unidentified) | 26 | 2020 |
| plant | Iris foetidissima | Stinking Iris | 740 | 2024 |
| plant | Iris foetidissima var. citrina | a flowering plant | 1 | 1998 |
| plant | Iris germanica | Bearded Iris | 20 | 2016 |
| plant | Iris orientalis | Turkish Iris | 3 | 2019 |
| plant | Iris pseudacorus | Yellow Flag | 1759 | 2024 |
| plant | Iris sibirica | Siberian Iris | 5 | 2019 |
| plant | Iris sp. cultivar | a garden iris | 2 | 2000 |
| plant | Iris spuria | Blue Iris | 2 | 1999 |
| plant | Iris tuberosa | Snake's-head Iris | 19 | 2014 |
| plant | Iris versicolor | Purple Iris | 1 | 2017 |
| plant | Isatis tinctoria | Woad | 11 | 2023 |
| plant | Isolepis cernua | Slender Club-rush | 6 | 2012 |
| plant | Isolepis setacea | Bristle Club-rush | 83 | 2016 |
| plant | Iva xanthiifolia | Marsh-elder | 2 | 2003 |
| springtail | Isotoma | an Isotoma species (unidentified) | 1 | 2013 |
| springtail | Isotoma riparia | a springtail (Collembola) | 1 | 2017 |
| springtail | Isotoma viridis | a springtail (Collembola) | 3 | 2012 |
| springtail | Isotomurus palustris | a springtail (Collembola) | 1 | 2011 |
| stonefly | Isoperla grammatica | a stonefly | 4 | 2025 |
| tick or mite (acarine) | Ixodes | an Ixodes species (unidentified) | 10 | 2023 |
| tick or mite (acarine) | Ixodes (Exopalpiger) trianguliceps | Vole or Shrew tick | 1 | 2016 |
| tick or mite (acarine) | Ixodes (Ixodes) frontalis | a hard tick | 2 | 1975 |
| tick or mite (acarine) | Ixodes (Ixodes) hexagonus | Hedgehog tick | 2 | 2022 |
| tick or mite (acarine) | Ixodes (Ixodes) ricinus | Sheep Tick | 183 | 2024 |
| tick or mite (acarine) | Ixodida | a tick (unidentified) | 4 | 2016 |
| true fly - | Ilione albiseta | a snail-killing fly | 13 | 2022 |
| true fly - | Ilythea spilota | a shore fly | 1 | 2001 |
| true fly - | Imantimyia albiseta | a fly | 7 | 2002 |
| true fly - | Incertella zuercheri | a fly | 1 | 2000 |
| true fly - | Ischiolepta pusilla | a lesser dung fly | 1 | 1994 |
| true fly - cranefly | Ilisia maculata | a cranefly | 6 | 2022 |
| true fly - midge, gnat or mosquito | Iteomyia capreae | a gall midge | 5 | 2020 |
| true fly - midge, gnat or mosquito | Iteomyia major | a gall midge | 2 | 2020 |
| woodlouse | Idotea chelipes | a sea slater | 5 | 1940 |
| woodlouse | Isopoda | a woodlouse or slater (unidentified) | 193 | 2017 |