Mites

You pull a sweater from the back of the closet on the first cool morning of the season, and by afternoon you are nursing an itchy rash across your shoulders, wondering if something crawled out of the upholstery. What unites these creatures in a single group is not a shared family tree, but their microscopic scale and unsegmented bodies, which means the various bugs lumped into this category actually behave in entirely opposite ways.
A house dust mite in your mattress survives quietly on shed skin flakes and triggers indoor allergies, while an oak leaf itch mite falling from a backyard tree drops in only to bite, and a bird mite migrating out of an attic vent is simply searching for a host after the birds left their nest. You can tell this group apart from insects in your kitchen or basement because they have eight legs instead of six and lack distinct body segments, though figuring out which specific microscopic visitor you are dealing with usually requires looking past the mere fact of their tiny size.
Explore mites
House dust mitesDermatophagoides species
Bird mitesDermanyssus and Ornithonyssus species
Tropical rat miteOrnithonyssus bacoti
Clover mitesBryobia species
ChiggersFamily Trombiculidae
Twospotted spider miteTetranychus urticae
Concrete / sidewalk mitesBalaustium species
Oak leaf itch mitePyemotes herfsi