Udea fulvalis
- Group
- Butterflies and moths
- Peak month
- July
- Records since 2000
- 266
Ugly Milkcap
- Group
- Fungi
- Peak month
- October
- Records since 2000
- 1,148
Ula mollissima
- Group
- True flies
- Peak month
- May
- Records since 2000
- 154
Ula sylvatica
- Group
- True flies
- Peak month
- July
- Records since 2000
- 277
Uleiota planatus
- Group
- Beetles
- Peak month
- May
- Records since 2000
- 298
Uloborus plumipes
- Group
- Spiders
- Peak month
- October
- Records since 2000
- 57
Ulomyia fuliginosa
- Group
- True flies
- Peak month
- July
- Records since 2000
- 94
Ulosa digitata
- Group
- Sponges
- Peak month
- May
- Records since 2000
- 126
Ulota crispula
- Group
- Mosses
- Peak month
- August
- Records since 2000
- 372
Ulota intermedia
- Group
- Mosses
- Peak month
- July
- Records since 2000
- 216
Ulothrix flacca
- Group
- Seaweeds and algae
- Peak month
- May
- Records since 2000
- 74
Ulothrix speciosa
- Group
- Seaweeds and algae
- Peak month
- June
- Records since 2000
- 59
Ulva clathrata
- Group
- Seaweeds and algae
- Peak month
- September
- Records since 2000
- 110
Ulva compressa
- Group
- Seaweeds and algae
- Peak month
- July
- Records since 2000
- 254
Ulva flexuosa
- Group
- Seaweeds and algae
- Peak month
- September
- Records since 2000
- 148
Ulva prolifera
- Group
- Seaweeds and algae
- Peak month
- June
- Records since 2000
- 255
Ulva pseudocurvata
- Group
- Seaweeds and algae
- Peak month
- September
- Records since 2000
- 99
Ulva rigida
- Group
- Seaweeds and algae
- Peak month
- August
- Records since 2000
- 111
Umbellifer Mildew
- Group
- Fungi
- Peak month
- September
- Records since 2000
- 1,403
Umbelopsis isabellina
- Group
- Fungi
- Peak month
- January
- Records since 2000
- 122
Umbilicaria cylindrica
- Group
- Lichens
- Peak month
- May
- Records since 2000
- 397
Umbilicaria polyrrhiza
- Group
- Lichens
- Peak month
- June
- Records since 2000
- 166
Unarmed Stick-insect
- Group
- Other insects
- Peak month
- September
- Records since 2000
- 193
Unbranched Bur-reed
- Group
- Flowering plants
- Peak month
- August
- Records since 2000
- 1,148
Unciola crenatipalma
- Group
- Crustaceans
- Peak month
- August
- Records since 2000
- 2,843
Unciola planipes
- Group
- Crustaceans
- Peak month
- July
- Records since 2000
- 645
Undulate Ray
- Group
- Fish
- Peak month
- October
- Records since 2000
- 3,705
Undulated False Lucine
- Group
- Molluscs
- Peak month
- September
- Records since 2000
- 1,567
Unguiculariopsis lettaui
- Group
- Fungi
- Peak month
- April
- Records since 2000
- 55
Unguiculariopsis thallophila
- Group
- Fungi
- Peak month
- January
- Records since 2000
- 153
Upland frenchman
- Group
- Beetles
- Peak month
- June
- Records since 2000
- 148
Upland Sandpiper
- Group
- Birds
- Peak month
- October
- Records since 2000
- 112
Upogebia deltaura
- Group
- Crustaceans
- Peak month
- August
- Records since 2000
- 2,332
Upogebia stellata
- Group
- Crustaceans
- Peak month
- May
- Records since 2000
- 217
Upright Brown Grimmia
- Group
- Mosses
- Peak month
- July
- Records since 2000
- 554
Upright Chickweed
- Group
- Flowering plants
- Peak month
- May
- Records since 2000
- 306
Upright Coral
- Group
- Fungi
- Peak month
- October
- Records since 2000
- 494
Upright Hedge-parsley
- Group
- Flowering plants
- Peak month
- July
- Records since 2000
- 3,778
Upright Pottia
- Group
- Mosses
- Peak month
- January
- Records since 2000
- 677
Upright Spurge
- Group
- Flowering plants
- Peak month
- July
- Records since 2000
- 54
Urban bluebottle blowfly, European blowfly
- Group
- True flies
- Peak month
- April
- Records since 2000
- 3,361
Urn Haircap
- Group
- Mosses
- Peak month
- July
- Records since 2000
- 4,682
Urocystis anemones
- Group
- Fungi
- Peak month
- May
- Records since 2000
- 143
Urocystis eranthidis
- Group
- Fungi
- Peak month
- April
- Records since 2000
- 79
Urocystis ranunculi
- Group
- Fungi
- Peak month
- September
- Records since 2000
- 150
Urocystis violae
- Group
- Fungi
- Peak month
- May
- Records since 2000
- 54
Uroleucon jaceae
- Group
- True bugs
- Peak month
- June
- Records since 2000
- 176
Uromunna petiti
- Group
- Crustaceans
- Peak month
- August
- Records since 2000
- 161
Uromyces acetosae
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 51
Uromyces airae-flexuosae
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 73
Uromyces behenis
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 68
Uromyces betae
- Group
- Fungi
- Peak month
- June
- Records since 2000
- 68
Uromyces fallens
- Group
- Fungi
- Peak month
- July
- Records since 2000
- 55
Uromyces geranii
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 194
Uromyces junci
- Group
- Fungi
- Peak month
- June
- Records since 2000
- 56
Uromyces lineolatus
- Group
- Fungi
- Peak month
- June
- Records since 2000
- 71
Uromyces pisi-sativi
- Group
- Fungi
- Peak month
- September
- Records since 2000
- 162
Uromyces polygoni-avicularis
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 75
Uromyces rumicis
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 272
Uromyces valerianae
- Group
- Fungi
- Peak month
- July
- Records since 2000
- 151
Uromyces viciae-fabae
- Group
- Fungi
- Peak month
- July
- Records since 2000
- 247
Urophora jaceana
- Group
- True flies
- Peak month
- June
- Records since 2000
- 446
Urophora stylata
- Group
- True flies
- Peak month
- June
- Records since 2000
- 226
Urothoe brevicornis
- Group
- Crustaceans
- Peak month
- June
- Records since 2000
- 1,096
Urothoe elegans
- Group
- Crustaceans
- Peak month
- June
- Records since 2000
- 6,137
Urothoe marina
- Group
- Crustaceans
- Peak month
- August
- Records since 2000
- 2,097
Urothoe poseidonis
- Group
- Crustaceans
- Peak month
- May
- Records since 2000
- 867
Urtica membranacea
- Group
- Flowering plants
- Peak month
- March
- Records since 2000
- 76
Usnea dasopoga
- Group
- Lichens
- Peak month
- March
- Records since 2000
- 85
Usnea dasypoga
- Group
- Lichens
- Peak month
- June
- Records since 2000
- 444
Usnea flammea
- Group
- Lichens
- Peak month
- April
- Records since 2000
- 703
Usnea wasmuthii
- Group
- Lichens
- Peak month
- May
- Records since 2000
- 449
Ustilago avenae
- Group
- Fungi
- Peak month
- June
- Records since 2000
- 190
Ustilago filiformis
- Group
- Fungi
- Peak month
- June
- Records since 2000
- 84
Ustilago striiformis
- Group
- Fungi
- Peak month
- May
- Records since 2000
- 50
Uzbekistanica vitis-viniferae
- Group
- Fungi
- Peak month
- August
- Records since 2000
- 1,620