A tiny black speck indoors is usually one of five things: a carpet beetle, a pantry beetle, a fungus gnat, a springtail or a booklouse. Whether it flies, jumps or only crawls narrows that to one or two in about ten seconds, and the room it came out of settles most of what is left.
What makes this hard is that almost every small insect reads as black across a kitchen counter, when the published colors run from reddish brown to mottled tan. So the sorting below leans on behavior and size instead, because those are what you can judge from where you are standing.
How big is it, really?
Get a number before anything else. Memory inflates insects, and in this group the difference between 1/16 inch and 1/4 inch is the difference between four different answers. Put a dime or a grain of rice beside it, or photograph it with something known in the frame.
The useful bands are these. Roughly 1 to 2 mm, under a tenth of an inch, is springtail and booklouse territory. Around 1/16 to 1/8 inch, which is 1.6 to 3 mm, covers carpet beetle adults and fungus gnats. From 1/8 to 1/4 inch, or 3 to 6 mm, covers the cupboard beetles and carpet beetle larvae.
Does it fly, jump or only crawl?
That one question splits the five cleanly. A thing that flies weakly and keeps drifting back to the window is a fungus gnat. A thing that vanishes when you reach for it, without ever appearing to run, is a springtail. A thing that walks, and only walks, is a beetle or a booklouse, and then the room decides which.
It flies, and it came off a houseplant
Fungus gnats. UC IPM describes them as dark, delicate-looking flies similar in appearance to mosquitoes, with slender legs and segmented antennae longer than their head. Adults commonly run about 1/16 to 1/8 inch (1.6 to 3 mm) long.
Two habits confirm it. UC IPM notes that adults are attracted to light, so you often notice them flying near windows first, and that they are relatively weak fliers that do not move around much indoors, tending to stay near potted plants and to run across the surface of growing media. The larvae live in the soil and have a shiny black head on an elongated, whitish, legless body. Where conditions are very wet, UC IPM says the larvae can leave slime trails on the media surface that look like the trails of small snails or slugs.
Adult fungus gnats do not damage plants and do not bite people. If the small flier came from the sink or the shower rather than a plant pot, read the fungus gnat and fruit fly comparison and the drain fly guide instead, because those three get mixed up constantly.
It walks, and it came out of a cupboard
Then it is one of the stored product beetles, and the University of Kentucky’s pantry fact sheet puts most of them at the same size. Red and confused flour beetles, cigarette beetles, drugstore beetles and sawtoothed grain beetles are all described as 1/8 inch (3 mm) long and red brown, which is exactly the color that reads as black on a white counter.
Their flight behavior is the cheapest way to split them. Kentucky records that confused flour beetles fly and are attracted to lights, that red flour beetles crawl toward light but apparently do not fly, and that sawtoothed grain beetles neither fly nor are drawn to light. Drugstore and cigarette beetle adults can fly and are attracted to light.
The other cupboard regular is bigger and shaped differently. Kentucky gives the rice weevil as 1/8 to 1/4 inch (3 to 6 mm) long, reddish brown to black, and a snout beetle, which means it has a visible downturned snout no flour beetle has. Adults can live six to eight months and may be found some distance from whatever they came out of, which is why they turn up in rooms with no food in them.
Kentucky also makes a point worth keeping: the first sign of a problem is usually small beetles crawling over counter tops, and in general the greater the number of insects seen, the older the problem is. The weevils and flour beetles guide works through which jar to open first.
It jumps, and the room is damp
Springtails. Penn State puts most of the types that get into homes at 1 to 2 mm long, with colors across the group running from white to black and through purple, red, orange, gray and yellow.
The jump is the identification. Penn State describes a furcula, a forked appendage folded under the fourth abdominal segment and held in place by a clasp called the tenaculum, which snaps downward and can propel the animal up to 100 times its body length. Nothing else in this size range moves like that, and it is why a springtail seems to teleport rather than run.
They need humidity. Penn State notes they feed on molds, mildew, fungi, bacteria and decaying plant material, that indoor populations are more common in bathrooms and basements, and that they move indoors under doors, sill plates, siding and windows during extended droughts or prolonged saturating rains. A springtail on the bathroom floor in a dry week usually came from a pot of overwatered soil.
It walks, it is oval, and it turned up on a rug or a sill
Carpet beetles. Kentucky describes the adults as small, 1/16 to 1/8 inch (1.6 to 3 mm), oval-shaped beetles ranging in color from black through various mottled patterns of white, brown, yellow and orange. Adults feed on flower pollen and do no damage to fabric at all. Kentucky notes that they often appear on windowsills in springtime, which suggests the real population is somewhere inside the house.
The larva is the one that matters and it looks nothing like the adult: 1/8 to 1/4 inch (3 to 6 mm) long, tan to brownish, slow moving, and densely covered with hairs or bristles, leaving shed skins behind as it grows. It digests keratin, so Kentucky lists wool, felt, fur, silk, feathers and leather among its foods, and notes that edges and undersides of rugs are more likely to be affected than open floor. It can also live on lint and hair under baseboards and in floor vents, and on accumulations of dead insects in attics and light fixtures. The carpet beetle guide covers the larva in detail.
It is barely visible, and the wall or the flour is damp
Booklice, which are neither lice nor much to do with books. Penn State gives them as 1 to 2 mm, soft-bodied and wingless, flattened top to bottom so they are wider than they are thick, mostly light to dark tan but sometimes gray, dark brown, orange-brown or nearly clear. The head is wide and carries a large clypeus that reads as a big nose.
They live on mold and fungi, which makes them an indicator of humidity rather than of dirt. Penn State also handles the fear this insect usually triggers: booklice are sometimes confused with bed bugs, but a bed bug is larger and rounder with a head proportionally narrower than its body, and to scale an adult bed bug is about three times the length of an adult booklouse. Booklice do not bite and are not vectors of disease. If that is the worry, the bed bug lookalikes guide sets the whole group side by side.
Which of these will a photograph not settle?
The cupboard beetles, mostly. Kentucky files flour beetles, cigarette beetles, drugstore beetles and sawtoothed grain beetles at one size and one color, and separating them means reading antenna segments and the edge of the thorax under magnification. For those, the cupboard tells you more than the beetle does, and a county extension office will put a specimen under a scope for you.
Once the list is down to two, a photograph closes it faster than another paragraph will. Bug Identifier reads one photo and returns the common name, the other names it goes by, the scientific name and classification, a description of the appearance so you can check the match against the insect in front of you, and its role, meaning whether it is beneficial, harmless or a pest and to what. Every scan stays in a dated collection, which turns out to be useful when the same speck reappears in March.
Whatever the answer is, this site stops at the name. For treatment of anything you decide is a problem, your local university extension service or a licensed professional is the right source, and if a sting or a bite has caused a reaction, that is a question for a doctor or poison control. To work from the room instead of the insect, start at what bug is this, or browse all the guides.