- Mabel Orchard Orbweaver
- Magnificent Frigatebird
- Magnolia Green Jumping Spider
- Magnolia Warbler
- Magpie-lark
- Maize Calligrapher
- Malachite
- Malayan Night Heron
- Mallard
- Mallow Scrub-Hairstreak
- Mallow Skipper
- Mandarin Duck
- Mantled Howler Monkey
- Map
- Maple Looper Moth
- Maple Spanworm Moth
- Marbled Carpet Moth
- Marbled Cellar Spider
- Marbled Crab
- Marbled Godwit
- Marbled Orbweaver
- Marbled White
- Marbled White-spot
- Margined Calligrapher
- Margined Leatherwing Beetle
- Margined White
- Marine Blue
- Marmalade Hover Fly
- Maroon-legged Lion Fly
- Marsh Fritillary
- Marsh Frog
- Marsh Rabbit
- Marsh Sandpiper
- Marsh Tit
- Marsh Wren
- Masked Hunter
- Masked Lapwing
- Masked Tityra
- Masked Water-Tyrant
- Master's Dart
- Mazarine Blue
- Meadow Argus
- Meadow Brown
- Meadow Fritillary
- Meadow Grasshopper
- Meadow Pipit
- Meadow Plant Bug
- Meadow Scorpionfly
- Meadow Spittlebug
- Meal moth
- Mediterranean Acrobat Ant
- Mediterranean Banded Centipede
- Mediterranean Conehead Mantis
- Mediterranean Damselfish
- Mediterranean Gull
- Mediterranean House Gecko
- Mediterranean Katydid
- Mediterranean Mantis
- Mediterranean Rainbow Wrasse
- Mediterranean Spiny False Wolf Spider
- Mediterranean Spotted Chafer
- Medium Egret
- Merlin
- Metric Paper Wasp
- Mexican Duck
- Mexican Fritillary
- Mexican Grass-carrying Wasp
- Mexican Jay
- Mexican Long-nosed Armadillo
- Mexican Treefrog
- Middle Spotted Woodpecker
- Migrant Hawker
- Migrant Hover Fly
- Migratory Locust
- Milbert's Tortoiseshell
- Milk Snail
- Milkweed Assassin Bug
- Milkweed Tussock Moth
- Milky Slug
- Mint Moth
- Mississippi Kite
- Mistle Thrush
- Modest Sphinx
- Monarch
- Monk Parakeet
- Montagu's Harrier
- Monterey Dorid
- Montezuma Oropendola
- Moonglow Anemone
- Moonseed Moth
- Moor Frog
- Moorish Gecko
- Moorish Idol
- Moose
- Morbid Owlet
- Morelet's Seedeater
- Morning-glory Plume Moth
- Mossy Chiton
- Mossy Rose Gall Wasp
- Mother of Pearl
- Mottled Beauty
- Mottled dingy-brown click beetle
- Mottled Duck
- Mottled Star
- Mottled Stink Bug
- Mottled Umber
- Mountain Bluebird
- Mountain Chickadee
- Mournful Duskywing
- Mourning Cloak
- Mourning Dove
- Mourning Gecko
- Mule Deer
- Musk beetle
- Muskrat
- Mute Swan
- Mylitta Crescent