There are 127 insects that start with the letter O, from Oak Aphid to Orthoporus Millipede. Below you will find them listed alphabetically along with some general information about each. Click the toggle view buttons in the top right corner to switch between the card and the table view.
For each item you will find the following information
Order: The subclass the insects belongs to
Habitat: The places or type of weather the insects lives in
Scientific name: The designation that scientists use to catalog the species
Name: Oak Aphid
Order: Hemiptera
Habitat: Oak Trees
Scientific name: Myzocallis spp.
Name: Oak Gall Wasp
Order: Hymenoptera
Habitat: Oak Trees
Scientific name: Cynipidae
Name: Oak Lace Bug
Order: Hemiptera
Habitat: Oak trees
Scientific name: Corythucha arcuata
Name: Oak Leaf Phylloxera
Order: Hemiptera
Habitat: Oak trees
Scientific name: Phylloxera spp.
Name: Oak Leaf Skeletonizer
Order: Lepidoptera
Habitat: Oak Trees
Scientific name: Bucculatrix ainsliella
Name: Oak Leafminer
Order: Lepidoptera
Habitat: Oak trees
Scientific name: Phyllonorycter crastaegella
Name: Oak Lecanium Scale
Order: Hemiptera
Habitat: Oak trees
Scientific name: Parthenolecanium quercifex
Name: Oak Orb Weaver
Order: Araneae
Habitat: Deciduous forests
Scientific name: Neoscona crucifera
Name: Oaky Oak Borer
Order: Coleoptera
Habitat: Oak trees
Scientific name: Phymatodes difficilis
Name: Oblique-banded Leaf Roller
Order: Lepidoptera
Habitat: Deciduous forests
Scientific name: Choristoneura rosaceana
Name: Oblique-banded Looper
Order: Lepidoptera
Habitat: Forest
Scientific name: Choristoneura rosaceana
Name: Oblique-banded Owlet Moth
Order: Lepidoptera
Habitat: Forest
Scientific name: Pandemis limitata
Name: Oblique-lined Flower Longhorn Beetle
Order: Coleoptera
Habitat: Forest
Scientific name: Strangalia obliqua
Name: Obliquebanded Leafroller
Order: Lepidoptera
Habitat: Deciduous forests
Scientific name: Choristoneura rosaceana
Name: Oblong Winged Katydid
Order: Orthoptera
Habitat: Woodlands
Scientific name: Amblycorypha oblongifolia
Name: Obscure Bird Grasshopper
Order: Orthoptera
Habitat: Meadows
Scientific name: Schistocerca obscura
Name: Obscure Cicada
Order: Hemiptera
Habitat: Deciduous forests
Scientific name: Melampsalta pruinosa
Name: Obscure Clubtail
Order: Odonata
Habitat: Streams and rivers
Scientific name: Gomphus oklahomensis
Name: Obscure Crane Fly
Order: Diptera
Habitat: Wetlands
Scientific name: Tipula obscura
Name: Obscure Darkling Beetle
Order: Coleoptera
Habitat: Leaf Litter
Scientific name: Blapstinus spp.
Name: Obscure Flat Bug
Order: Hemiptera
Habitat: Woodlands
Scientific name: Aradus spp.
Name: Obscure Fungus Beetle
Order: Coleoptera
Habitat: Moist forests
Scientific name: Oxylaemus californicus
Name: Obscure Fungus Gnat
Order: Diptera
Habitat: Forest
Scientific name: Mycetophila obscura
Name: Obscure Fungus Weevil
Order: Coleoptera
Habitat: Decaying wood
Scientific name: Bactridium spp.
Name: Obscure Grasshopper
Order: Orthoptera
Habitat: Grasslands
Scientific name: Hippiscus obscurus
Name: Obscure Ground Beetle
Order: Coleoptera
Habitat: Leaf Litter
Scientific name: Harpalus spp.
Name: Obscure Ground Centipede
Order: Scolopendromorpha
Habitat: Soil
Scientific name: Scolopocryptops spp.
Name: Obscure Ground Hopper
Order: Orthoptera
Habitat: Grasslands
Scientific name: Tetrix spp.
Name: Obscure Ichneumon Wasp
Order: Hymenoptera
Habitat: Woodlands
Scientific name: Enicospilus spp.
Name: Obscure Leaf-footed Bug
Order: Hemiptera
Habitat: Forests
Scientific name: Leptoglossus spp.
Name: Obscure Looper
Order: Lepidoptera
Habitat: Wooded areas
Scientific name: Nematocampa resistaria
Name: Obscure Mosquito
Order: Diptera
Habitat: Wetlands
Scientific name: Anopheles spp.
Name: Obscure Rove Beetle
Order: Coleoptera
Habitat: Decaying matter
Scientific name: Atheta spp.
Name: Obscure Sac Spider
Order: Araneae
Habitat: Woodlands
Scientific name: Clubiona spp.
Name: Obscure Scarab Beetle
Order: Coleoptera
Habitat: Decaying matter
Scientific name: Oniticellus spp.
Name: Obscure Snipe Fly
Order: Diptera
Habitat: Marshes
Scientific name: Rhagio spp.
Name: Obscure Sphinx Moth
Order: Lepidoptera
Habitat: Forest
Scientific name: Sphinx poecila
Name: Obscure Springtail
Order: Collembola
Habitat: Soil
Scientific name: Oncopodura spp.
Name: Obscure Stink Bug
Order: Hemiptera
Habitat: Forests
Scientific name: Acrosternum spp.
Name: Obscure Tree Cricket
Order: Orthoptera
Habitat: Forest
Scientific name: Oecanthus obscurus
Name: Obscure Treehopper
Order: Hemiptera
Habitat: Forests
Scientific name: Publilia spp.
Name: Obscure Weevil
Order: Coleoptera
Habitat: Oak forests
Scientific name: Trigonoscuta obscura
Name: Obscured Brocade Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Lacanobia obscura
Name: Obstructed Fungus Beetle
Order: Coleoptera
Habitat: Forest
Scientific name: Agathengis obstructus
Name: Ocean Cockroach
Order: Blattodea
Habitat: Coastal areas
Scientific name: Parcoblatta lata
Name: Ocellated Cerambycid Beetle
Order: Coleoptera
Habitat: Forest
Scientific name: Oberea oculata
Name: Ocellated Crab Spider
Order: Araneae
Habitat: Forests
Scientific name: Thomisus onustus
Name: Ocellated Crane Fly
Order: Diptera
Habitat: Wetlands
Scientific name: Pedicia ocellata
Name: Ocellated Darkling Beetle
Order: Coleoptera
Habitat: Deserts
Scientific name: Eusattus reticulatus
Name: Ocellated Ground Beetle
Order: Coleoptera
Habitat: Woodlands
Scientific name: Dicaelus dilatatus
Name: Ocellated Hover Fly
Order: Diptera
Habitat: Forest
Scientific name: Syrphus ocellatus
Name: Ocellated Stink Bug
Order: Hemiptera
Habitat: Deciduous forests
Scientific name: Stiretrus anchorago
Name: Ocellated Tiger Beetle
Order: Coleoptera
Habitat: Sandy areas
Scientific name: Cicindela ocellata
Name: Ochraceous Calzada Moth
Order: Lepidoptera
Habitat: Grasslands
Scientific name: Erebidae
Name: Ochraceous Drab Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Erebidae
Name: Ochraceous Hermit Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Erebidae
Name: Ochraceous Hoaxer Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Erebidae
Name: Ochraceous Midget Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Depressariidae
Name: Ochraceous Pseudoscorpion
Order: Pseudoscorpionida
Habitat: Leaf litter
Scientific name: Chelifer cancroides
Name: Ochraceous Snout Moth
Order: Lepidoptera
Habitat: Grasslands
Scientific name: Pyralidae
Name: Ochre Ant
Order: Hymenoptera
Habitat: Forest
Scientific name: Lasius umbratus
Name: Ochre Butterfly
Order: Lepidoptera
Habitat: Forest
Scientific name: Nathalis iole
Name: Ochre Darkling Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Melandrya spp.
Name: Ochre Ground Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Chlaenius spp.
Name: Ochre Lacewing
Order: Neuroptera
Habitat: Forests
Scientific name: Hemerobius spp.
Name: Ochre Leaf Beetle
Order: Coleoptera
Habitat: Forests
Scientific name: Phyllobrotica spp.
Name: Ochre Longhorn Beetle
Order: Coleoptera
Habitat: Forests
Scientific name: Rhagium spp.
Name: Ochre Moth
Order: Lepidoptera
Habitat: Deciduous forests
Scientific name: Haploa clymene
Name: Ochre Planthopper
Order: Hemiptera
Habitat: Grasslands
Scientific name: Chloriona spp.
Name: Ochre Snout Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Hypena spp.
Name: Ochre Tortricid Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Epinotia spp.
Name: Ochre Wood Cricket
Order: Orthoptera
Habitat: Forests
Scientific name: Oecanthus spp.
Name: Ochre-cloaked Beetle
Order: Coleoptera
Habitat: Forests
Scientific name: Tenebrionidae
Name: Ochre-headed Ground Beetle
Order: Coleoptera
Habitat: Forest
Scientific name: Pterostichus ochropus
Name: Ochre-legged Darkling Beetle
Order: Coleoptera
Habitat: Deserts
Scientific name: Tenebrionidae
Name: Ochre-legged Grasshopper
Order: Orthoptera
Habitat: Grasslands
Scientific name: Acrididae
Name: Ochre-lined Darkling Beetle
Order: Coleoptera
Habitat: Deserts
Scientific name: Tenebrionidae
Name: Ochre-lined Tortoise Beetle
Order: Coleoptera
Habitat: Forests
Scientific name: Chrysomelidae
Name: Ochre-patched Ground Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Carabidae
Name: Ochre-patterned Darkling Beetle
Order: Coleoptera
Habitat: Deserts
Scientific name: Tenebrionidae
Name: Ochre-spotted Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Erebidae
Name: Ochre-tinted Darkling Beetle
Order: Coleoptera
Habitat: Deserts
Scientific name: Tenebrionidae
Name: Ochre-winged Beetle
Order: Coleoptera
Habitat: Forests
Scientific name: Tenebrionidae
Name: Ochreous Ground Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Amara spp.
Name: Ochreous Ladybird Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Coccinellidae
Name: Ochreous Leafhopper
Order: Hemiptera
Habitat: Forests
Scientific name: Empoasca spp.
Name: Ochreous Looper Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Geometridae
Name: Ochreous Pug Moth
Order: Lepidoptera
Habitat: Coniferous forests
Scientific name: Eupithecia ochreata
Name: Ochreous Quaker Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Noctuidae
Name: Ochreous Sallow Moth
Order: Lepidoptera
Habitat: Forest
Scientific name: Sunira verberata
Name: Ochreous Scavenger Beetle
Order: Coleoptera
Habitat: Decaying matter
Scientific name: Monotoma spp.
Name: Ochreous Spanworm Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Geometridae
Name: Ochreous Umbel Moth
Order: Lepidoptera
Habitat: Grasslands
Scientific name: Depressariidae
Name: Ochropus Ground Beetle
Order: Coleoptera
Habitat: Forests
Scientific name: Carabidae
Name: Octagonal Darkling Beetle
Order: Coleoptera
Habitat: Arid regions
Scientific name: Eleodes octangularis
Name: Octalasion Awl Moth
Order: Lepidoptera
Habitat: Grasslands
Scientific name: Hepialidae
Name: Octoblepharum Moss
Order: Bryophyta
Habitat: Forest
Scientific name: Octoblepharum albidum
Name: Ogre-faced Spider
Order: Araneae
Habitat: Tropical forests
Scientific name: Deinopis spinosa
Name: Ohio Leatherwing
Order: Coleoptera
Habitat: Deciduous forests
Scientific name: Chauliognathus pensylvanicus
Name: Olaus's Tortoise Beetle
Order: Coleoptera
Habitat: Forest
Scientific name: Cassida olauxi
Name: Old World Longhorn Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Achroia spp.
Name: Old World Webworm
Order: Lepidoptera
Habitat: Prairies
Scientific name: Loxostege sticticalis
Name: Olivaceous Owlet Moth
Order: Lepidoptera
Habitat: Forest
Scientific name: Bryophila algae
Name: Olive Fruit Fly
Order: Diptera
Habitat: Olive Groves
Scientific name: Bactrocera oleae
Name: Olive Jumping Spider
Order: Araneae
Habitat: Urban areas
Scientific name: Phidippus otiosus
Name: Olive-backed Pocket Mouse
Order: Rodentia
Habitat: Forest
Scientific name: Perognathus fasciatus
Name: Olive-brown Darkling Beetle
Order: Coleoptera
Habitat: Forest
Scientific name: Upis ceramboides
Name: Olive-gray Ground Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Harpalus spp.
Name: Olive-gray Shield Bug
Order: Hemiptera
Habitat: Forests
Scientific name: Aelia spp.
Name: Olive-green Carpet Beetle
Order: Coleoptera
Habitat: Homes
Scientific name: Anthrenus oliveirae
Name: Olive-green Emerald Moth
Order: Lepidoptera
Habitat: Forest
Scientific name: Geometra papilionaria
Name: Olive-green Snout Moth
Order: Lepidoptera
Habitat: Deciduous forests
Scientific name: Hypena olivacea
Name: Olive-sided Flycatcher
Order: Diptera
Habitat: Coniferous forests
Scientific name: Contopus cooperi
Name: Olive-tree Scale
Order: Hemiptera
Habitat: Olive trees
Scientific name: Parlatoria oleae
Name: Olive-tree Whitefly
Order: Hemiptera
Habitat: Olive trees
Scientific name: Aleyrodes olivinus
Name: Olynthus Beetle
Order: Coleoptera
Habitat: Grasslands
Scientific name: Olynthus spp.
Name: Ominous Beetle
Order: Coleoptera
Habitat: Rotting wood
Scientific name: Nicrophorus americanus
Name: Omnivorous Cockroach
Order: Blattodea
Habitat: Buildings
Scientific name: Blatta orientalis
Name: Opaque Darkling Beetle
Order: Coleoptera
Habitat: Deserts
Scientific name: Eleodes hispilabris
Name: Opaque Mantidfly
Order: Neuroptera
Habitat: Deciduous forests
Scientific name: Climaciella brunnea
Name: Ophicocordyceps Fungus Moth
Order: Lepidoptera
Habitat: Forests
Scientific name: Ophiocordyceps unilateralis
Name: Orange Dart
Order: Lepidoptera
Habitat: Deciduous forests
Scientific name: Axylia putris
Name: Orange Scavenger Fly
Order: Diptera
Habitat: Grasslands
Scientific name: Gymnonerius fuscus
Name: Orchard Longhorn Beetle
Order: Coleoptera
Habitat: Orchards
Scientific name: Prionus laticollis
Name: Oriental Cockroach
Order: Blattodea
Habitat: Urban areas
Scientific name: Blatta orientalis
Name: Ornate Fly
Order: Diptera
Habitat: Grasslands
Scientific name: Syrphidae
Name: Orthoporus Millipede
Order: Diplopoda
Habitat: Leaf litter
Scientific name: Orthoporus ornatus
| Name | Order | Habitat | Scientific name |
|---|---|---|---|
| Oak Aphid | Hemiptera | Oak Trees | Myzocallis spp. |
| Oak Gall Wasp | Hymenoptera | Oak Trees | Cynipidae |
| Oak Lace Bug | Hemiptera | Oak trees | Corythucha arcuata |
| Oak Leaf Phylloxera | Hemiptera | Oak trees | Phylloxera spp. |
| Oak Leaf Skeletonizer | Lepidoptera | Oak Trees | Bucculatrix ainsliella |
| Oak Leafminer | Lepidoptera | Oak trees | Phyllonorycter crastaegella |
| Oak Lecanium Scale | Hemiptera | Oak trees | Parthenolecanium quercifex |
| Oak Orb Weaver | Araneae | Deciduous forests | Neoscona crucifera |
| Oaky Oak Borer | Coleoptera | Oak trees | Phymatodes difficilis |
| Oblique-banded Leaf Roller | Lepidoptera | Deciduous forests | Choristoneura rosaceana |
| Oblique-banded Looper | Lepidoptera | Forest | Choristoneura rosaceana |
| Oblique-banded Owlet Moth | Lepidoptera | Forest | Pandemis limitata |
| Oblique-lined Flower Longhorn Beetle | Coleoptera | Forest | Strangalia obliqua |
| Obliquebanded Leafroller | Lepidoptera | Deciduous forests | Choristoneura rosaceana |
| Oblong Winged Katydid | Orthoptera | Woodlands | Amblycorypha oblongifolia |
| Obscure Bird Grasshopper | Orthoptera | Meadows | Schistocerca obscura |
| Obscure Cicada | Hemiptera | Deciduous forests | Melampsalta pruinosa |
| Obscure Clubtail | Odonata | Streams and rivers | Gomphus oklahomensis |
| Obscure Crane Fly | Diptera | Wetlands | Tipula obscura |
| Obscure Darkling Beetle | Coleoptera | Leaf Litter | Blapstinus spp. |
| Obscure Flat Bug | Hemiptera | Woodlands | Aradus spp. |
| Obscure Fungus Beetle | Coleoptera | Moist forests | Oxylaemus californicus |
| Obscure Fungus Gnat | Diptera | Forest | Mycetophila obscura |
| Obscure Fungus Weevil | Coleoptera | Decaying wood | Bactridium spp. |
| Obscure Grasshopper | Orthoptera | Grasslands | Hippiscus obscurus |
| Obscure Ground Beetle | Coleoptera | Leaf Litter | Harpalus spp. |
| Obscure Ground Centipede | Scolopendromorpha | Soil | Scolopocryptops spp. |
| Obscure Ground Hopper | Orthoptera | Grasslands | Tetrix spp. |
| Obscure Ichneumon Wasp | Hymenoptera | Woodlands | Enicospilus spp. |
| Obscure Leaf-footed Bug | Hemiptera | Forests | Leptoglossus spp. |
| Obscure Looper | Lepidoptera | Wooded areas | Nematocampa resistaria |
| Obscure Mosquito | Diptera | Wetlands | Anopheles spp. |
| Obscure Rove Beetle | Coleoptera | Decaying matter | Atheta spp. |
| Obscure Sac Spider | Araneae | Woodlands | Clubiona spp. |
| Obscure Scarab Beetle | Coleoptera | Decaying matter | Oniticellus spp. |
| Obscure Snipe Fly | Diptera | Marshes | Rhagio spp. |
| Obscure Sphinx Moth | Lepidoptera | Forest | Sphinx poecila |
| Obscure Springtail | Collembola | Soil | Oncopodura spp. |
| Obscure Stink Bug | Hemiptera | Forests | Acrosternum spp. |
| Obscure Tree Cricket | Orthoptera | Forest | Oecanthus obscurus |
| Obscure Treehopper | Hemiptera | Forests | Publilia spp. |
| Obscure Weevil | Coleoptera | Oak forests | Trigonoscuta obscura |
| Obscured Brocade Moth | Lepidoptera | Forests | Lacanobia obscura |
| Obstructed Fungus Beetle | Coleoptera | Forest | Agathengis obstructus |
| Ocean Cockroach | Blattodea | Coastal areas | Parcoblatta lata |
| Ocellated Cerambycid Beetle | Coleoptera | Forest | Oberea oculata |
| Ocellated Crab Spider | Araneae | Forests | Thomisus onustus |
| Ocellated Crane Fly | Diptera | Wetlands | Pedicia ocellata |
| Ocellated Darkling Beetle | Coleoptera | Deserts | Eusattus reticulatus |
| Ocellated Ground Beetle | Coleoptera | Woodlands | Dicaelus dilatatus |
| Ocellated Hover Fly | Diptera | Forest | Syrphus ocellatus |
| Ocellated Stink Bug | Hemiptera | Deciduous forests | Stiretrus anchorago |
| Ocellated Tiger Beetle | Coleoptera | Sandy areas | Cicindela ocellata |
| Ochraceous Calzada Moth | Lepidoptera | Grasslands | Erebidae |
| Ochraceous Drab Moth | Lepidoptera | Forests | Erebidae |
| Ochraceous Hermit Moth | Lepidoptera | Forests | Erebidae |
| Ochraceous Hoaxer Moth | Lepidoptera | Forests | Erebidae |
| Ochraceous Midget Moth | Lepidoptera | Forests | Depressariidae |
| Ochraceous Pseudoscorpion | Pseudoscorpionida | Leaf litter | Chelifer cancroides |
| Ochraceous Snout Moth | Lepidoptera | Grasslands | Pyralidae |
| Ochre Ant | Hymenoptera | Forest | Lasius umbratus |
| Ochre Butterfly | Lepidoptera | Forest | Nathalis iole |
| Ochre Darkling Beetle | Coleoptera | Grasslands | Melandrya spp. |
| Ochre Ground Beetle | Coleoptera | Grasslands | Chlaenius spp. |
| Ochre Lacewing | Neuroptera | Forests | Hemerobius spp. |
| Ochre Leaf Beetle | Coleoptera | Forests | Phyllobrotica spp. |
| Ochre Longhorn Beetle | Coleoptera | Forests | Rhagium spp. |
| Ochre Moth | Lepidoptera | Deciduous forests | Haploa clymene |
| Ochre Planthopper | Hemiptera | Grasslands | Chloriona spp. |
| Ochre Snout Moth | Lepidoptera | Forests | Hypena spp. |
| Ochre Tortricid Moth | Lepidoptera | Forests | Epinotia spp. |
| Ochre Wood Cricket | Orthoptera | Forests | Oecanthus spp. |
| Ochre-cloaked Beetle | Coleoptera | Forests | Tenebrionidae |
| Ochre-headed Ground Beetle | Coleoptera | Forest | Pterostichus ochropus |
| Ochre-legged Darkling Beetle | Coleoptera | Deserts | Tenebrionidae |
| Ochre-legged Grasshopper | Orthoptera | Grasslands | Acrididae |
| Ochre-lined Darkling Beetle | Coleoptera | Deserts | Tenebrionidae |
| Ochre-lined Tortoise Beetle | Coleoptera | Forests | Chrysomelidae |
| Ochre-patched Ground Beetle | Coleoptera | Grasslands | Carabidae |
| Ochre-patterned Darkling Beetle | Coleoptera | Deserts | Tenebrionidae |
| Ochre-spotted Moth | Lepidoptera | Forests | Erebidae |
| Ochre-tinted Darkling Beetle | Coleoptera | Deserts | Tenebrionidae |
| Ochre-winged Beetle | Coleoptera | Forests | Tenebrionidae |
| Ochreous Ground Beetle | Coleoptera | Grasslands | Amara spp. |
| Ochreous Ladybird Beetle | Coleoptera | Grasslands | Coccinellidae |
| Ochreous Leafhopper | Hemiptera | Forests | Empoasca spp. |
| Ochreous Looper Moth | Lepidoptera | Forests | Geometridae |
| Ochreous Pug Moth | Lepidoptera | Coniferous forests | Eupithecia ochreata |
| Ochreous Quaker Moth | Lepidoptera | Forests | Noctuidae |
| Ochreous Sallow Moth | Lepidoptera | Forest | Sunira verberata |
| Ochreous Scavenger Beetle | Coleoptera | Decaying matter | Monotoma spp. |
| Ochreous Spanworm Moth | Lepidoptera | Forests | Geometridae |
| Ochreous Umbel Moth | Lepidoptera | Grasslands | Depressariidae |
| Ochropus Ground Beetle | Coleoptera | Forests | Carabidae |
| Octagonal Darkling Beetle | Coleoptera | Arid regions | Eleodes octangularis |
| Octalasion Awl Moth | Lepidoptera | Grasslands | Hepialidae |
| Octoblepharum Moss | Bryophyta | Forest | Octoblepharum albidum |
| Ogre-faced Spider | Araneae | Tropical forests | Deinopis spinosa |
| Ohio Leatherwing | Coleoptera | Deciduous forests | Chauliognathus pensylvanicus |
| Olaus's Tortoise Beetle | Coleoptera | Forest | Cassida olauxi |
| Old World Longhorn Moth | Lepidoptera | Forests | Achroia spp. |
| Old World Webworm | Lepidoptera | Prairies | Loxostege sticticalis |
| Olivaceous Owlet Moth | Lepidoptera | Forest | Bryophila algae |
| Olive Fruit Fly | Diptera | Olive Groves | Bactrocera oleae |
| Olive Jumping Spider | Araneae | Urban areas | Phidippus otiosus |
| Olive-backed Pocket Mouse | Rodentia | Forest | Perognathus fasciatus |
| Olive-brown Darkling Beetle | Coleoptera | Forest | Upis ceramboides |
| Olive-gray Ground Beetle | Coleoptera | Grasslands | Harpalus spp. |
| Olive-gray Shield Bug | Hemiptera | Forests | Aelia spp. |
| Olive-green Carpet Beetle | Coleoptera | Homes | Anthrenus oliveirae |
| Olive-green Emerald Moth | Lepidoptera | Forest | Geometra papilionaria |
| Olive-green Snout Moth | Lepidoptera | Deciduous forests | Hypena olivacea |
| Olive-sided Flycatcher | Diptera | Coniferous forests | Contopus cooperi |
| Olive-tree Scale | Hemiptera | Olive trees | Parlatoria oleae |
| Olive-tree Whitefly | Hemiptera | Olive trees | Aleyrodes olivinus |
| Olynthus Beetle | Coleoptera | Grasslands | Olynthus spp. |
| Ominous Beetle | Coleoptera | Rotting wood | Nicrophorus americanus |
| Omnivorous Cockroach | Blattodea | Buildings | Blatta orientalis |
| Opaque Darkling Beetle | Coleoptera | Deserts | Eleodes hispilabris |
| Opaque Mantidfly | Neuroptera | Deciduous forests | Climaciella brunnea |
| Ophicocordyceps Fungus Moth | Lepidoptera | Forests | Ophiocordyceps unilateralis |
| Orange Dart | Lepidoptera | Deciduous forests | Axylia putris |
| Orange Scavenger Fly | Diptera | Grasslands | Gymnonerius fuscus |
| Orchard Longhorn Beetle | Coleoptera | Orchards | Prionus laticollis |
| Oriental Cockroach | Blattodea | Urban areas | Blatta orientalis |
| Ornate Fly | Diptera | Grasslands | Syrphidae |
| Orthoporus Millipede | Diplopoda | Leaf litter | Orthoporus ornatus |