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| Common Name | Scientific Name | Order | Family | Genus | Species | Author | notes |
|---|---|---|---|---|---|---|---|
| twospotted bumble bee | Bombus bimaculatus (Cresson) | HYMENOPTERA | Apidae | Bombus | bimaculatus | (Cresson) | |
| twospotted grass bug | Stenotus binotatus (Fabricius) | HEMIPTERA | Miridae | Stenotus | binotatus | (Fabricius) | |
| twospotted lady beetle | Adalia bipunctata (Linnaeus) | COLEOPTERA | Coccinellidae | Adalia | bipunctata | (Linnaeus) | |
| twospotted spider mite | Tetranychus urticae Koch | ACARI | Tetranychidae | Tetranychus | urticae | Koch | |
| twospotted stink bug | Perillus bioculatus (Fabricius) | HEMIPTERA | Pentatomidae | Perillus | bioculatus | (Fabricius) | |
| twostriped grasshopper | Melanoplus bivittatus (Say) | ORTHOPTERA | Acrididae | Melanoplus | bivittatus | (Say) | |
| twostriped walkingstick | Anisomorpha buprestoides (Stoll) | PHASMATODEA | Pseudophasmatidae | Anisomorpha | buprestoides | (Stoll) | |
| uglynest caterpillar | Archips cerasivorana (Fitch) | LEPIDOPTERA | Tortricidae | Archips | cerasivorana | (Fitch) | |
| unicorn caterpillar | Schizura unicornis (J.E. Smith) | LEPIDOPTERA | Notodontidae | Schizura | unicornis | (J.E. Smith) | |
| vagabond crambus | Agriphila vulgivagella (Clemens) | LEPIDOPTERA | Crambidae | Agriphila | vulgivagella | (Clemens) | |
| vagrant grasshopper | Schistocerca nitens nitens (Thunberg) | ORTHOPTERA | Acrididae | Schistocerca | nitens nitens | (Thunberg) | |
| Van Duzee treehopper | Vanduzea segmentata (Fowler) | HEMIPTERA | Membracidae | Vanduzea | segmentata | (Fowler) | |
| van Dyke bumble bee | Bombus vandykei Frison | HYMENOPTERA | Apidae | Bombus | vandykei | Frison | |
| vanda thrips | Dichromothrips corbetti (Priesner) | THYSANOPTERA | Thripidae | Dichromothrips | corbetti | (Priesner) | |
| variable cuckoo bumble bee | Bombus variabilis (Cresson) | HYMENOPTERA | Apidae | Bombus | variabilis | (Cresson) | |
| variable oakleaf caterpillar | Lochmaeus manteo (Doubleday) | LEPIDOPTERA | Notodontidae | Lochmaeus | manteo | (Doubleday) | |
| varied carpet beetle | Anthrenus verbasci (Linnaeus) | COLEOPTERA | Dermestidae | Anthrenus | verbasci | (Linnaeus) | |
| variegated cutworm | Peridroma saucia (Hübner) | LEPIDOPTERA | Noctuidae | Peridroma | saucia | (Hübner) | |
| vedalia | Rodolia cardinalis (Mulsant) | COLEOPTERA | Coccinellidae | Rodolia | cardinalis | (Mulsant) | |
| vegetable leafminer | Liriomyza sativae Blanchard | DIPTERA | Agromyzidae | Liriomyza | sativae | Blanchard | |
| vegetable weevil | Listroderes difficilis Germar | COLEOPTERA | Curculionidae | Listroderes | difficilis | Germar | |
| velvetbean caterpillar | Anticarsia gemmatalis Hübner | LEPIDOPTERA | Noctuidae | Anticarsia | gemmatalis | Hübner | |
| verbena bud moth | Endothenia hebesana (Walker) | LEPIDOPTERA | Tortricidae | Endothenia | hebesana | (Walker) | |
| verde plant bug | Creontiades signatus Distant | HEMIPTERA | Miridae | Creontiades | signatus | Distant | |
| vespiform thrips | Franklinothrips vespiformis (D.L. Crawford) | THYSANOPTERA | Aeolothripidae | Franklinothrips | vespiformis | (D.L. Crawford) | |
| vetch bruchid | Bruchus brachialis (Förster) | COLEOPTERA | Chrysomelidae | Bruchus | brachialis | (Förster) | |
| vexans mosquito | Aedes vexans (Meigen) | DIPTERA | Culicidae | Aedes | vexans | (Meigen) | |
| viburnum aphid | Aphis viburniphila Patch | HEMIPTERA | Aphididae | Aphis | viburniphila | Patch | |
| viburnum leaf beetle | Pyrrhalta viburni (Paykull) | COLEOPTERA | Chrysomelidae | Pyrrhalta | viburni | (Paykull) | |
| viceroy | Limenitis archippus (Cramer) | LEPIDOPTERA | Nymphalidae | Limenitis | archippus | (Cramer) | |
| violet aphid | Neotoxoptera violae (Pergande) | HEMIPTERA | Aphididae | Neotoxoptera | violae | (Pergande) | |
| violet sawfly | Ametastegia pallipes (Spinola) | HYMENOPTERA | Tenthredinidae | Ametastegia | pallipes | (Spinola) | |
| Virginia pine sawfly | Neodiprion pratti pratti (Dyar) | HYMENOPTERA | Diprionidae | Neodiprion | pratti pratti | (Dyar) | |
| Virginiacreeper leafhopper | Erythroneura ziczac Walsh | HEMIPTERA | Cicadellidae | Erythroneura | ziczac | Walsh | |
| Virginiacreeper sphinx | Darapsa myron (Cramer) | LEPIDOPTERA | Sphingidae | Darapsa | myron | (Cramer) | |
| Vosnesensky bumble bee | Bombus vosnesenskii Radoszkowski | HYMENOPTERA | Apidae | Bombus | vosnesenskii | Radoszkowski | |
| w-marked cutworm | Spaelotis clandestina (Harris) | LEPIDOPTERA | Noctuidae | Spaelotis | clandestina | (Harris) | |
| walkingstick | Diapheromera femorata (Say) | PHASMATODEA | Heteronemiidae | Diapheromera | femorata | (Say) | |
| walnut aphid | Chromaphis juglandicola (Kaltenbach) | HEMIPTERA | Aphididae | Chromaphis | juglandicola | (Kaltenbach) | |
| walnut blister mite | Aceria erinea (Nalepa) | ACARI | Eriophyidae | Aceria | erinea | (Nalepa) | |
| walnut caterpillar | Datana integerrima Grote & Robinson | LEPIDOPTERA | Notodontidae | Datana | integerrima | Grote & Robinson | |
| walnut husk fly | Rhagoletis completa Cresson | DIPTERA | Tephritidae | Rhagoletis | completa | Cresson | |
| walnut scale | Quadraspidiotus juglansregiae (Comstock) | HEMIPTERA | Diaspididae | Quadraspidiotus | juglansregiae | (Comstock) | |
| walnut shoot moth | Acrobasis demotella Grote | LEPIDOPTERA | Pyralidae | Acrobasis | demotella | Grote | |
| walnut sphinx | Laothoe juglandis (J.E. Smith) | LEPIDOPTERA | Sphingidae | Laothoe | juglandis | (J.E. Smith) | |
| walnut twig beetle | Pityophthorus juglandis (Blackman) | COLEOPTERA | Curculionidae | Pityophthorus | juglandis | (Blackman) | |
| wardrobe beetle | Attagenus fasciatus (Thunberg) | COLEOPTERA | Dermestidae | Attagenus | fasciatus | (Thunberg) | |
| warehouse beetle | Trogoderma variabile Ballion | COLEOPTERA | Dermestidae | Trogoderma | variabile | Ballion | |
| warehouse pirate bug | Xylocoris flavipes (Reuter) | HEMIPTERA | Anthocoridae | Xylocoris | flavipes | (Reuter) | |
| Warren root collar weevil | Hylobius warreni Wood | COLEOPTERA | Curculionidae | Hylobius | warreni | Wood | |
| warty grain mite | Aeroglyphus robustus (Banks) | ACARI | Glycyphagidae | Aeroglyphus | robustus | (Banks) | |
| watercress leaf beetle | Phaedon laevigatus (Duftschmid) | COLEOPTERA | Chrysomelidae | Phaedon | laevigatus | (Duftschmid) | |
| watercress sharpshooter | Draeculacephala mollipes (Say) | HEMIPTERA | Cicadellidae | Draeculacephala | mollipes | (Say) | |
| watercress sowbug | Lirceus brachyurus (Harger) | ISOPODA | Asellidae | Lirceus | brachyurus | (Harger) | |
| waterlily aphid | Rhopalosiphum nymphaeae (Linnaeus) | HEMIPTERA | Aphididae | Rhopalosiphum | nymphaeae | (Linnaeus) | |
| waterlily leaf beetle | Galerucella nymphaeae (Linnaeus) | COLEOPTERA | Chrysomelidae | Galerucella | nymphaeae | (Linnaeus) | |
| waterlily leafcutter | Synclita obliteralis (Walker) | LEPIDOPTERA | Crambidae | Synclita | obliteralis | (Walker) | |
| webbing clothes moth | Tineola bisselliella (Hummel) | LEPIDOPTERA | Tineidae | Tineola | bisselliella | (Hummel) | |
| webbing coneworm | Dioryctria disclusa Heinrich | LEPIDOPTERA | Pyralidae | Dioryctria | disclusa | Heinrich | |
| West Indian cane weevil | Metamasius hemipterus hemipterus (Linnaeus) | COLEOPTERA | Curculionidae | Metamasius | hemipterus hemipterus | (Linnaeus) | |
| West Indian flatid | Anormenis antillarum (Kirkaldy) | HEMIPTERA | Flatidae | Anormenis | antillarum | (Kirkaldy) | |
| West Indian fruit fly | Anastrepha obliqua (Macquart) | DIPTERA | Tephritidae | Anastrepha | obliqua | (Macquart) | |
| West Indian sweetpotato weevil | Euscepes postfaciatus (Fairmaire) | COLEOPTERA | Curculionidae | Euscepes | postfaciatus | (Fairmaire) | |
| western balsam bark beetle | Dryocoetes confusus Swaine | COLEOPTERA | Curculionidae | Dryocoetes | confusus | Swaine | |
| western bat bug | Cimex pilosellus (Hovarth) | HEMIPTERA | Cimicidae | Cimex | pilosellus | (Hovarth) | |
| western bean cutworm | Striacosta albicosta (Smith) | LEPIDOPTERA | Noctuidae | Striacosta | albicosta | (Smith) | |
| western bigeyed bug | Geocoris pallens Stål | HEMIPTERA | Geocoridae | Geocoris | pallens | Stål | |
| western black flea beetle | Phyllotreta pusilla Horn | COLEOPTERA | Chrysomelidae | Phyllotreta | pusilla | Horn | |
| western black widow spider | Latrodectus hesperus Chamberlin & Ivie | ARANEAE | Theridiidae | Latrodectus | hesperus | Chamberlin & Ivie | |
| western blackheaded budworm | Acleris gloverana (Walsingham) | LEPIDOPTERA | Tortricidae | Acleris | gloverana | (Walsingham) | |
| western blacklegged tick | Ixodes pacificus Cooley & Kohls | ACARI | Ixodidae | Ixodes | pacificus | Cooley & Kohls | |
| western bloodsucking conenose | Triatoma protracta (Uhler) | HEMIPTERA | Reduviidae | Triatoma | protracta | (Uhler) | |
| western boxelder bug | Boisea rubrolineata (Barber) | HEMIPTERA | Rhopalidae | Boisea | rubrolineata | (Barber) | |
| western cedar bark beetle | Phloeosinus punctatus LeConte | COLEOPTERA | Curculionidae | Phloeosinus | punctatus | LeConte | |
| western cedar borer | Trachykele blondeli Marseul | COLEOPTERA | Buprestidae | Trachykele | blondeli | Marseul | |
| western cherry fruit fly | Rhagoletis indifferens Curran | DIPTERA | Tephritidae | Rhagoletis | indifferens | Curran | |
| western chicken flea | Ceratophyllus niger (Fox) | SIPHONAPTERA | Ceratophyllidae | Ceratophyllus | niger | (Fox) | |
| western chinch bug | Blissus occiduus Barber | HEMIPTERA | Blissidae | Blissus | occiduus | Barber | |
| western cicada killer | Sphecius grandis (Say) | HYMENOPTERA | Crabronidae | Sphecius | grandis | (Say) | |
| western conifer-seed bug | Leptoglossus occidentalis Heidemann | HEMIPTERA | Coreidae | Leptoglossus | occidentalis | Heidemann | |
| western corn rootworm | Diabrotica virgifera virgifera LeConte | COLEOPTERA | Chrysomelidae | Diabrotica | virgifera virgifera | LeConte | |
| western damsel bug | Nabis alternatus Parshley | HEMIPTERA | Nabidae | Nabis | alternatus | Parshley | |
| western drywood termite | Incisitermes minor (Hagen) | ISOPTERA | Kalotermitidae | Incisitermes | minor | (Hagen) | |
| western field wireworm | Limonius infuscatus Motschulsky | COLEOPTERA | Elateridae | Limonius | infuscatus | Motschulsky | |
| western flower thrips | Frankliniella occidentalis (Pergande) | THYSANOPTERA | Thripidae | Frankliniella | occidentalis | (Pergande) | |
| western grape leafhopper | Erythroneura elegantula Osborn | HEMIPTERA | Cicadellidae | Erythroneura | elegantula | Osborn | |
| western grape rootworm | Bromius obscurus (Linnaeus) | COLEOPTERA | Chrysomelidae | Bromius | obscurus | (Linnaeus) | |
| western grapeleaf skeletonizer | Harrisina brillians Barnes & McDunnough | LEPIDOPTERA | Zygaenidae | Harrisina | brillians | Barnes & McDunnough | |
| western harvester ant | Pogonomyrmex occidentalis (Cresson) | HYMENOPTERA | Formicidae | Pogonomyrmex | occidentalis | (Cresson) | |
| western hemlock looper | Lambdina fiscellaria lugubrosa (Hulst) | LEPIDOPTERA | Geometridae | Lambdina | fiscellaria lugubrosa | (Hulst) | |
| western lawn moth | Tehama bonifatella (Hulst) | LEPIDOPTERA | Crambidae | Tehama | bonifatella | (Hulst) | |
| western lily aphid | Ericaphis scoliopi (Essig) | HEMIPTERA | Aphididae | Ericaphis | scoliopi | (Essig) | |
| western oak looper | Lambdina fiscellaria somniaria (Hulst) | LEPIDOPTERA | Geometridae | Lambdina | fiscellaria somniaria | (Hulst) | |
| western pine beetle | Dendroctonus brevicomis LeConte | COLEOPTERA | Curculionidae | Dendroctonus | brevicomis | LeConte | |
| western pine budworm | Choristoneura lambertiana (Busck) | LEPIDOPTERA | Tortricidae | Choristoneura | lambertiana | (Busck) | |
| western pine cone beetle | Conophthorus ponderosae Hopkins | COLEOPTERA | Curculionidae | Conophthorus | ponderosae | Hopkins | |
| western pine shoot borer | Eucosma sonomana Kearfott | LEPIDOPTERA | Tortricidae | Eucosma | sonomana | Kearfott | |
| western pine tip moth | Rhyacionia bushnelli (Busck) | LEPIDOPTERA | Tortricidae | Rhyacionia | bushnelli | (Busck) | |
| western pine tussock moth | Dasychira grisefacta (Dyar) | LEPIDOPTERA | Lymantriidae | Dasychira | grisefacta | (Dyar) | |
| western plant bug | Rhinacloa forticornis Reuter | HEMIPTERA | Miridae | Rhinacloa | forticornis | Reuter | |
| western poplar clearwing | Paranthrene robiniae (Hy. Edwards) | LEPIDOPTERA | Sesiidae | Paranthrene | robiniae | (Hy. Edwards) | |
| western potato flea beetle | Epitrix subcrinita LeConte | COLEOPTERA | Chrysomelidae | Epitrix | subcrinita | LeConte | |
| western potato leafhopper | Empoasca abrupta DeLong | HEMIPTERA | Cicadellidae | Empoasca | abrupta | DeLong | |
| western predatory mite | Galendromus occidentalis (Nesbitt) | ACARI | Phytoseiidae | Galendromus | occidentalis | (Nesbitt) | |
| western spotted cucumber beetle | Diabrotica undecimpunctata undecimpunctata Mannerheim | COLEOPTERA | Chrysomelidae | Diabrotica | undecimpunctata undecimpunctata | Mannerheim | |
| western spruce budworm | Choristoneura occidentalis Freeman | LEPIDOPTERA | Tortricidae | Choristoneura | occidentalis | Freeman | |
| western striped cucumber beetle | Acalymma trivittatum (Mannerheim) | COLEOPTERA | Chrysomelidae | Acalymma | trivittatum | (Mannerheim) | |
| western striped flea beetle | Phyllotreta ramosa (Crotch) | COLEOPTERA | Chrysomelidae | Phyllotreta | ramosa | (Crotch) | |
| western subterranean termite | Reticulitermes hesperus Banks | ISOPTERA | Rhinotermitidae | Reticulitermes | hesperus | Banks | |
| western tarnished plant bug | Lygus hesperus Knight | HEMIPTERA | Miridae | Lygus | hesperus | Knight | |
| western tent caterpillar | Malacosoma californicum (Packard) | LEPIDOPTERA | Lasiocampidae | Malacosoma | californicum | (Packard) | |
| western thatching ant | Formica obscuripes Forel | HYMENOPTERA | Formicidae | Formica | obscuripes | Forel | |
| western treehole mosquito | Aedes sierrensis (Ludlow) | DIPTERA | Culicidae | Aedes | sierrensis | (Ludlow) | |
| western tussock moth | Orgyia vetusta Boisduval | LEPIDOPTERA | Lymantriidae | Orgyia | vetusta | Boisduval | |
| western w-marked cutworm | Spaelotis bicava LaFontaine | LEPIDOPTERA | Noctuidae | Spaelotis | bicava | LaFontaine | |
| western wheat aphid | Diuraphis tritici (Gillette) | HEMIPTERA | Aphididae | Diuraphis | tritici | (Gillette) | |
| western yellowjacket | Vespula pensylvanica (Saussure) | HYMENOPTERA | Vespidae | Vespula | pensylvanica | (Saussure) | |
| western yellowstriped armyworm | Spodoptera praefica (Grote) | LEPIDOPTERA | Noctuidae | Spodoptera | praefica | (Grote) | |
| wharf borer | Nacerdes melanura (Linnaeus) | COLEOPTERA | Oedemeridae | Nacerdes | melanura | (Linnaeus) | |
| wheat curl mite | Aceria tosichella Keifer | ACARI | Eriophyidae | Aceria | tosichella | Keifer | |
| wheat head armyworm | Faronta diffusa (Walker) | LEPIDOPTERA | Noctuidae | Faronta | diffusa | (Walker) | |
| wheat jointworm | Tetramesa tritici (Fitch) | HYMENOPTERA | Eurytomidae | Tetramesa | tritici | (Fitch) | |
| wheat midge | Sitodiplosis mosellana (Géhin) | DIPTERA | Cecidomyiidae | Sitodiplosis | mosellana | (Géhin) | |
| wheat stem maggot | Meromyza americana Fitch | DIPTERA | Chloropidae | Meromyza | americana | Fitch | |
| wheat stem sawfly | Cephus cinctus Norton | HYMENOPTERA | Cephidae | Cephus | cinctus | Norton | |
| wheat strawworm | Tetramesa grandis (Riley) | HYMENOPTERA | Eurytomidae | Tetramesa | grandis | (Riley) | |
| wheat wireworm | Agriotes mancus (Say) | COLEOPTERA | Elateridae | Agriotes | mancus | (Say) | |
| wheel bug | Arilus cristatus (Linnaeus) | HEMIPTERA | Reduviidae | Arilus | cristatus | (Linnaeus) | |
| white apple leafhopper | Typhlocyba pomaria McAtee | HEMIPTERA | Cicadellidae | Typhlocyba | pomaria | McAtee | |
| white cutworm | Euxoa scandens (Riley) | LEPIDOPTERA | Noctuidae | Euxoa | scandens | (Riley) | |
| white fir needleminer | Epinotia meritana Heinrich | LEPIDOPTERA | Tortricidae | Epinotia | meritana | Heinrich | |
| white garden snail | Theba pisana (Müller) | STYLOMMATOPHORA | Helicidae | Theba | pisana | (Müller) | |
| white oak borer | Goes tigrinus (De Geer) | COLEOPTERA | Cerambycidae | Goes | tigrinus | (De Geer) | |
| white peach scale | Pseudaulacaspis pentagona (Targioni-Tozzetti) | HEMIPTERA | Diaspididae | Pseudaulacaspis | pentagona | (Targioni-Tozzetti) | |
| white pine aphid | Cinara strobi (Fitch) | HEMIPTERA | Aphididae | Cinara | strobi | (Fitch) | |
| white pine cone beetle | Conophthorus coniperda (Schwarz) | COLEOPTERA | Curculionidae | Conophthorus | coniperda | (Schwarz) | |
| white pine cone borer | Eucosma tocullionana Heinrich | LEPIDOPTERA | Tortricidae | Eucosma | tocullionana | Heinrich | |
| white pine sawfly | Neodiprion pinetum (Norton) | HYMENOPTERA | Diprionidae | Neodiprion | pinetum | (Norton) | |
| white pine weevil* | Pissodes strobi (Peck) | COLEOPTERA | Curculionidae | Pissodes | strobi | (Peck) | *Also called Englemann spruce weevil and Sitka spruce weevil |
| white-shouldered bumble bee | Bombus appositus Cresson | HYMENOPTERA | Apidae | Bombus | appositus | Cresson | |
| whitebacked garden spider | Argiope trifasciata (Forskal) | ARANEAE | Araneidae | Argiope | trifasciata | (Forskal) | |
| whitebanded elm leafhopper | Scaphoideus luteolus Van Duzee | HEMIPTERA | Cicadellidae | Scaphoideus | luteolus | Van Duzee | |
| whitecrossed seed bug | Neacoryphus bicrucis (Say) | HEMIPTERA | Lygaeidae | Neacoryphus | bicrucis | (Say) | |
| whitefringed beetles | Graphognathus spp. | COLEOPTERA | Curculionidae | Graphognathus | spp. | ||
| whitelined sphinx | Hyles lineata (Fabricius) | LEPIDOPTERA | Sphingidae | Hyles | lineata | (Fabricius) | |
| whitemargined cockroach | Melanozosteria soror (Brunner) | BLATTODEA | Blattidae | Melanozosteria | soror | (Brunner) | |
| whitemarked fleahopper | Spanagonicus albofasciatus (Reuter) | HEMIPTERA | Miridae | Spanagonicus | albofasciatus | (Reuter) | |
| whitemarked spider beetle | Ptinus fur (Linnaeus) | COLEOPTERA | Ptinidae | Ptinus | fur | (Linnaeus) | |
| whitemarked treehopper | Tricentrus albomaculatus Distant | HEMIPTERA | Membracidae | Tricentrus | albomaculatus | Distant | |
| whitemarked tussock moth | Orgyia leucostigma (J.E. Smith) | LEPIDOPTERA | Lymantriidae | Orgyia | leucostigma | (J.E. Smith) | |
| whiteshouldered house moth | Endrosis sarcitrella (Linnaeus) | LEPIDOPTERA | Oecophoridae | Endrosis | sarcitrella | (Linnaeus) | |
| whitespotted sawyer | Monochamus scutellatus scutellatus (Say) | COLEOPTERA | Cerambycidae | Monochamus | scutellatus scutellatus | (Say) | |
| Willamette spider mite | Eotetranychus willamettei (McGregor) | ACARI | Tetranychidae | Eotetranychus | willamettei | (McGregor) | |
| willow bark beetle | Trypophloeus striatulua (Mannerheim) | COLEOPTERA | Curculionidae | Trypophloeus | striatulua | (Mannerheim) | |
| willow beaked-gall midge | Rabdophaga rigidae (Osten Sacken) | DIPTERA | Cecidomyiidae | Rabdophaga | rigidae | (Osten Sacken) | |
| willow flea weevil | Rhynchaenus rufipes (LeConte) | COLEOPTERA | Curculionidae | Rhynchaenus | rufipes | (LeConte) | |
| willow redgall sawfly | Pontania promixa (Serville) | HYMENOPTERA | Tenthredinidae | Pontania | promixa | (Serville) | |
| willow sawfly | Nematus ventralis Say | HYMENOPTERA | Tenthredinidae | Nematus | ventralis | Say | |
| willow shoot sawfly | Janus abbreviatus (Say) | HYMENOPTERA | Cephidae | Janus | abbreviatus | (Say) | |
| Wilson sphinx | Hyles wilsoni (Rothschild) | LEPIDOPTERA | Sphingidae | Hyles | wilsoni | (Rothschild) | |
| wing louse | Lipeurus caponis (Linnaeus) | PHTHIRAPTERA | Philopteridae | Lipeurus | caponis | (Linnaeus) | |
| winter cutworm | Noctua pronuba (Linnaeus) | LEPIDOPTERA | Noctuidae | Noctua | pronuba | (Linnaeus) | |
| winter grain mite | Penthaleus major (Dugès) | ACARI | Eupodidae | Penthaleus | major | (Dugès) | |
| winter moth | Operophtera brumata (Linnaeus) | LEPIDOPTERA | Geometridae | Operophtera | brumata | (Linnaeus) | |
| winter tick | Dermacentor albipictus (Packard) | ACARI | Ixodidae | Dermacentor | albipictus | (Packard) | |
| woodrose bug | Graptostethus manillensis (Stål) | HEMIPTERA | Lygaeidae | Graptostethus | manillensis | (Stål) | |
| woods weevil | Nemocestes incomptus (Horn) | COLEOPTERA | Curculionidae | Nemocestes | incomptus | (Horn) | |
| woolly alder aphid | Prociphilus tessellatus (Fitch) | HEMIPTERA | Aphididae | Prociphilus | tessellatus | (Fitch) | |
| woolly apple aphid | Eriosoma lanigerum (Hausmann) | HEMIPTERA | Aphididae | Eriosoma | lanigerum | (Hausmann) | |
| woolly elm aphid | Eriosoma americanum (Riley) | HEMIPTERA | Aphididae | Eriosoma | americanum | (Riley) | |
| woolly pear aphid | Eriosoma pyricola Baker & Davidson | HEMIPTERA | Aphididae | Eriosoma | pyricola | Baker & Davidson | |
| woolly whitefly | Aleurothrixus floccosus (Maskell) | HEMIPTERA | Aleyrodidae | Aleurothrixus | floccosus | (Maskell) | |
| yellow and black potter wasp | Delta campaniforme campaniforme (Fabricius) | HYMENOPTERA | Vespidae | Delta | campaniforme campaniforme | (Fabricius) | |
| yellow bumble bee | Bombus fervidus (Fabricius) | HYMENOPTERA | Apidae | Bombus | fervidus | (Fabricius) | |
| yellow clover aphid | Therioaphis trifolii (Monell) | HEMIPTERA | Aphididae | Therioaphis | trifolii | (Monell) | |
| yellow garden spider | Argiope aurantia Lucas | ARANEAE | Araneidae | Argiope | aurantia | Lucas | |
| yellow head bumble bee | Bombus flavifrons Cresson | HYMENOPTERA | Apidae | Bombus | flavifrons | Cresson | |
| yellow mealworm | Tenebrio molitor Linnaeus | COLEOPTERA | Tenebrionidae | Tenebrio | molitor | Linnaeus | |
| yellow pecan aphid | Monelliopsis pecanis Bissell | HEMIPTERA | Aphididae | Monelliopsis | pecanis | Bissell | |
| yellow rose aphid | Rhodobium porosum (Sanderson) | HEMIPTERA | Aphididae | Rhodobium | porosum | (Sanderson) | |
| yellow scale | Aonidiella citrina (Coquillett) | HEMIPTERA | Diaspididae | Aonidiella | citrina | (Coquillett) | |
| yellow spider mite | Eotetranychus carpini borealis (Ewing) | ACARI | Tetranychidae | Eotetranychus | carpini borealis | (Ewing) | |
| yellow stem borer | Scirpophaga incertulas (Walker) | LEPIDOPTERA | Crambidae | Scirpophaga | incertulas | (Walker) | |
| yellow sugarcane aphid | Sipha flava (Forbes) | HEMIPTERA | Aphididae | Sipha | flava | (Forbes) | |
| yellow woollybear | Spilosoma virginica (Fabricius) | LEPIDOPTERA | Arctiidae | Spilosoma | virginica | (Fabricius) | |
| yellowbanded bumble bee | Bombus terricola (Kirby) | HYMENOPTERA | Apidae | Bombus | terricola | (Kirby) | |
| yellowfaced leafhopper | Scaphytopius loricatus (Van Duzee) | HEMIPTERA | Cicadellidae | Scaphytopius | loricatus | (Van Duzee) | |
| yellowfever mosquito | Aedes aegypti (Linnaeus) | DIPTERA | Culicidae | Aedes | aegypti | (Linnaeus) | |
| yellowheaded cutworm | Apamea amputatrix (Fitch) | LEPIDOPTERA | Noctuidae | Apamea | amputatrix | (Fitch) | |
| yellowheaded fireworm | Acleris minuta (Robinson) | LEPIDOPTERA | Tortricidae | Acleris | minuta | (Robinson) | |
| yellowheaded leafhopper | Xyphon flaviceps (Riley) | HEMIPTERA | Cicadellidae | Xyphon | flaviceps | (Riley) | |
| yellowheaded spruce sawfly | Pikonema alaskensis (Rohwer) | HYMENOPTERA | Tenthredinidae | Pikonema | alaskensis | (Rohwer) | |
| yellowmargined leaf beetle | Microtheca ochroloma Stål | COLEOPTERA | Chrysomelidae | Microtheca | ochroloma | Stål | |
| yellownecked caterpillar | Datana ministra (Drury) | LEPIDOPTERA | Notodontidae | Datana | ministra | (Drury) | |
| yellowshouldered lady beetle | Scymnodes lividigaster (Mulsant) | COLEOPTERA | Coccinellidae | Scymnodes | lividigaster | (Mulsant) | |
| yellowstriped armyworm | Spodoptera ornithogalli (Guenée) | LEPIDOPTERA | Noctuidae | Spodoptera | ornithogalli | (Guenée) | |
| Yosemite bark weevil | Pissodes schwarzi Hopkins | COLEOPTERA | Curculionidae | Pissodes | schwarzi | Hopkins | |
| yucca moth | Tegeticula yuccasella (Riley) | LEPIDOPTERA | Prodoxidae | Tegeticula | yuccasella | (Riley) | |
| yucca plant bug | Halticotoma valida Townsend | HEMIPTERA | Miridae | Halticotoma | valida | Townsend | |
| Yuma spider mite | Eotetranychus yumensis (McGregor) | ACARI | Tetranychidae | Eotetranychus | yumensis | (McGregor) | |
| zebra caterpillar | Melanchra picta (Harris) | LEPIDOPTERA | Noctuidae | Melanchra | picta | (Harris) | |
| Zimmerman pine moth | Dioryctria zimmermani (Grote) | LEPIDOPTERA | Pyralidae | Dioryctria | zimmermani | (Grote) |