No-see-ums are biting midges: small flies in the family Ceratopogonidae, most of the ones that bite people belonging to the genus Culicoides. Adults measure 1-3 mm, which is how they got the name. Females cut the skin with four tiny blades and lap the blood that pools in the opening. The bite burns at the time, then itches for days.
That is the short answer. The rest is about the consequences.
You will almost never see the insect that bit you. What you notice is a burning point on an ankle, a wrist, or the strip of skin where a sleeve ends. By the time a welt appears, the midge is gone. No amount of searching the patio will find it. That mismatch between the size of the insect and the size of the problem explains why no-see-ums generate so much frustration and so little useful advice.
Key takeaways
- A no-see-um is 1-3 mm long, about the size of a pencil tip. Only the female bites, and she needs a blood meal to develop eggs.
- The welt is an immune reaction to saliva, not damage from the wound. That is why the itch arrives late and lasts for days.
- Their larvae need damp soil and rotting organic matter, not open water. Emptying a birdbath does nothing for a salt marsh or a wet pasture.
- Most species travel less than 1 mile from where they developed, and they are weak fliers. Air movement and fine screens beat spraying.
- A CO₂ trap can catch no-see-ums while it catches mosquitoes. It is not a midge-control device, and treating it as one leads to disappointment.
What no-see-ums actually are
Biting midges are true flies. That means one pair of wings and a body built for short, erratic flight. The family is enormous. There are more than 4,000 described species across 78 genera worldwide, and over 600 species in 36 genera in North America alone (Purdue University Extension, Biting Midges).
Most of those species never touch a mammal. They feed on nectar or on other insects, and are invisible to us. Only four genera feed on mammalian blood. Three of them account for nearly every bite a person receives: Culicoides, Leptoconops, and Forcipomyia. That short list is good news. The insect on your ankle belongs to a small, well-studied group.
The naming causes most of the confusion. In North America the same insect is a no-see-um, a punky in the Northeast, a pinyon gnat in the Southwest, a moose fly in Canada, and a five-O in Florida and Alabama, where the local biting peak lands around five in the afternoon. Coastal visitors call them sand gnats. Every one of those names describes the same family.
Two lookalikes are worth separating out. Non-biting midges, the ones that form columns over a lake at dusk, belong to a different family. They have no mouthparts for biting. Sand flies are different again: the name usually refers to phlebotomine flies in the family Psychodidae, roughly 600 species worldwide with 14 in the United States, of which only one bites humans (Purdue University Extension). If something you cannot see is biting you, the odds strongly favour a midge.
| Insect | Size | Bites people? | Where the larvae develop |
|---|---|---|---|
| Biting midge (no-see-um) | 1-3 mm | Yes, females only | Damp soil, marsh edge, rotting organic matter |
| Mosquito | 3-9 mm | Yes, females only | Standing water in containers, drains, pools |
| Non-biting midge | 2-10 mm | No | Lake and river bottoms |
| Phlebotomine sand fly | 2-3 mm | Rarely, in the U.S. | Moist soil, animal burrows, cracks |
Why the bites burn now and itch later
A mosquito pierces skin with a needle-like bundle. A no-see-um does not. Its mouthparts sit inside a fleshy sheath that holds four minute cutting blades, and those blades lacerate the surface instead of sliding in (Purdue University Extension). The insect then feeds from the small pool of blood that forms.
That explains two things people notice about no-see-ums but rarely connect. The bite hurts immediately, often as a sharp sting, because tissue is being cut. The itch comes later and stays longer, because the reaction is to saliva left in the wound. Proteins in that saliva trigger a local allergic response. It can range from a small red welt to a swollen lump that lasts for days.
Clusters matter more than single bites with this insect. Nobody panics over one welt. The pattern that sends people looking for answers is eight or ten welts in a line along the ankle, or a band of bites where a hem met a sock. No-see-ums target thin, exposed skin, and they arrive in numbers because a host is a shared resource.
If you are dealing with the aftermath, the rule is simple: do not scratch. Broken skin turns a nuisance into a possible infection, and these bites itch long enough that scratching is almost guaranteed once you start. Wash the area, cool it, use an over-the-counter anti-itch product. If a bite swells far beyond the first welt, or you develop a fever after travelling in Central America, South America, or the Caribbean, that is a medical conversation rather than a gardening one.
For the equipment side, the difference between a CO₂-baited device and a light-based one is covered in our explanation of how CO₂ mosquito traps attract insects. The mechanism matters for both mosquitoes and no-see-ums.
Where no-see-ums come from (and why draining puddles won’t fix it)
This is where most advice goes wrong. Homeowners are trained by mosquito guidance to hunt for standing water, and that habit fails completely against no-see-ums.
Midge larvae develop in moist organic material: saturated soil, mud along a pond margin, marsh edge, bog, wet pasture, manure-rich ground, tree holes, rotting wood (Merck Veterinary Manual). Some species are genuinely aquatic and live in streams and ponds. Others need nothing more than permanent damp and something decaying to feed on. There is no container to tip out, no gutter to clear, no saucer under a flowerpot to empty.
That difference drives everything about control. Merck’s clinical guidance is blunt. These habitats are extensive, scattered, and hard to identify, so large-scale larval control is impractical in most situations. Management is therefore directed at reducing host exposure rather than suppressing the population. In plain terms, you will not eliminate the source. You interrupt the last 30 metres.
Distance is the other half of the picture. Most Culicoides females disperse no more than 0.5-1 mile from their development site, so a wetland three properties away can supply your garden indefinitely (Purdue University Extension). One genus, Leptoconops, can travel roughly 10 miles. That is why some arid-region properties are bitten by no-see-ums that developed far beyond the fence line.
The practical consequence: work out which direction the insects arrive from before you spend money. On still evenings, note where the first bites happen and which way the air is moving. A property downwind of a tidal creek, irrigated pasture, or shaded bog is fighting a supply line, not an infestation. That one observation changes which measures below are worth paying for.
When no-see-ums are active, and what wind does to them
Most Culicoides species begin feeding at dusk and continue into the night. Leptoconops species in arid regions feed during daylight (Purdue University Extension). Merck puts peak activity before and during dusk, in the warm months of the year. The five-O nickname from Florida is not folklore. It is a local observation of a daily peak.
Wind is the lever most people never pull. No-see-ums are weak fliers, and flight is greatly reduced or curtailed in windy conditions. Merck notes that increasing air movement with an electric fan can decrease host-seeking and feeding around animal housing. The same principle works on a patio. A ceiling fan on medium, or an oscillating fan aimed across the seating area, will do more on a still evening than a fogger will do all week.
Temperature and humidity set the season, and neither is something a homeowner can change. What you can change is when you use the space. Moving dinner from 7:30 to 5:30 sounds trivial until you try it on a coastal property in August. Same table, same guests, a fraction of the bites, because the daily peak had not started.
What actually reduces bites around a property
No single measure solves no-see-ums. What works is a stack of partial measures. They are ranked below by how much each one buys you per dollar.
Screens: the one intervention with a clear margin
Purdue’s guidance is unusually direct here. Screens with a mesh finer than normal window screening are much more effective at reducing bites than insecticide treatment, because the screen physically excludes the insect. Standard window screen is woven to stop houseflies and mosquitoes. A 2 mm no-see-um passes straight through it. Products sold as no-see-um screening use a tighter weave for exactly this reason.
If you are screening a porch, a lanai, or a bedroom window on a coastal property, specify the tighter mesh at the start. Retrofitting is expensive. A porch that keeps out mosquitoes but not no-see-ums will be judged a failure by everyone who uses it after dark.
Air movement
Covered above, and worth repeating because it is the cheapest item on this list. Air moving across a seating area disrupts the weak flight of a midge far more reliably than it disrupts a mosquito. Fans also break up the CO₂ plume that builds around a group of people sitting still.
Skin and clothing
Repellents help, but the evidence for this insect is thinner than for mosquitoes. Purdue’s summary is that DEET-based repellents and DEET- or permethrin-treated clothing give only limited protection against no-see-ums. Limited is not useless. A treated long-sleeve layer and repellent on exposed ankles will reduce the number of bites. It will not turn a salt-marsh evening into a comfortable one, and anyone promising that has not spent an evening on the coast.
Clothing matters as much as the chemical. Loose long sleeves, long trousers, and socks pulled over the ankle close the thin-skin targets these insects prefer. That is also the honest answer for families with small children. Physical coverage plus timing beats any product applied to a toddler’s skin.
Timing
Purdue ranks scheduling outdoor activity around the daily peaks as the most effective personal measure available. That is a striking statement from an extension service, and it should set your expectations for everything else. If bites cluster in a 90-minute window at dusk, moving the event out of that window is the decision with the most effect, and it costs nothing.
What about spraying?
Adulticide treatment gives temporary relief under specific conditions. Purdue notes short-term relief after evening aerial applications along the Atlantic and Gulf coasts, with the emphasis on temporary. On a single property, fogging kills the insects present at the moment of application. It does nothing about the population arriving from a marsh a quarter-mile away the next evening. It is a tool for an event, not a season.
If you are running a larger site and need to sequence these measures, the layered approach in our guide to controlling mosquitoes across a large outdoor area maps onto midge pressure with one adjustment. Source reduction carries less weight. Exposure management carries more.
Can a CO₂ trap help with no-see-ums?
This is the question buyers actually ask, and it deserves a straight answer rather than a product page.
Carbon dioxide is a shared cue. Female no-see-ums locate hosts largely in response to the CO₂ a host exhales (Purdue University Extension). That is the same signal that makes CO₂-baited traps work on mosquitoes. A device that releases CO₂ and draws air inward will therefore catch midges, which is why CO₂-baited suction traps are used in surveillance work. Catching them is not a claim that needs special pleading.
What that does not mean is that a CO₂ trap controls a midge population. Three limits matter.
First, the device is designed and rated for mosquitoes outdoors. The Pittar units carry an effective range of 4,000 m², inside a design band of roughly 50-4,000 m². Midge capture is incidental to that design, and no coverage rating exists for midges.
Second, midges are far more numerous per unit area near a breeding site. A trap that removes a meaningful share of the mosquitoes in a garden removes a much smaller share of a population emerging from a marsh.
Third, the insects are arriving from outside the property. A device inside the fence intercepts traffic. It does not stop the supply.
Where a CO₂ unit earns its place is on sites with mixed biting pressure: a resort terrace, a wedding lawn, a large garden where mosquitoes are the main complaint and midge bites are a secondary annoyance at dusk. There the trap reduces the mosquito population it was built for, and the no-see-ums it catches are a bonus rather than the justification.
Placement follows the same logic as mosquito work, with one addition. Put the unit between the insects and the people, on the upwind side of the area you use at dusk. Keep it away from the seating itself, so the plume competes with the guests rather than joining them. Our guide to where to place a CO₂ trap in a yard covers the geometry, and the same rules apply when no-see-ums are part of the mix.
If your property is dominated by midges rather than mosquitoes, be honest with yourself before buying. A trap will catch some. It will not change the character of a dusk on a tidal creek, and the money may be better spent on tighter screens and a fan. That is not a comfortable answer for a company that sells traps, which is exactly why it is worth saying.
Quick answers
Do no-see-ums carry disease?
In the United States, no biting midge is known to transmit a disease agent to humans, though they are serious livestock pests and vectors of bluetongue virus (Purdue University Extension). Internationally the picture differs. Oropouche virus spreads to people primarily through infected biting midges, particularly Culicoides paraensis, and has been reported in parts of South America, Central America, and the Caribbean (CDC, About Oropouche, reviewed 2026). Symptoms include sudden fever, severe headache, chills, muscle aches, and joint pain, usually lasting 2-7 days and sometimes recurring. There is no vaccine and no specific treatment, so bite prevention is the whole strategy.
How long do the bites last?
The burning fades within minutes. The itch typically peaks in the first 24-48 hours and can persist for several days, longer if scratching breaks the skin. Reactions vary widely, and people bitten repeatedly over years often react less.
Are repellents safe for children?
Follow the product label, which states the minimum age for that formulation. Apply to exposed skin rather than clothing on young children. Physical coverage and avoiding the dusk peak are the lower-risk options, and they work.
Do no-see-ums disappear in winter?
Activity in temperate regions stops when the warm months end, but the insects do not die out. The last larval stage overwinters and pupates the following spring or early summer (Purdue University Extension). The first warm still evening of the new season brings them back. A cold snap interrupts activity. It does not remove the population.
What to do next
If you have read this far, you probably fall into one of two groups.
If no-see-ums are biting on a property you live on, start with the free measures. Shift the evening hour, move air across the seating area, and check whether your screens are standard mesh. Those three changes cost little and address the mechanism that produces bites. Then decide whether any product is worth buying.
If you are specifying equipment for a larger commercial site, this is a planning question rather than a product question. Where do people sit at dusk, which direction do the insects arrive from, and is the dominant pressure mosquitoes or no-see-ums? Send us the site size, the hours the space is used, and what is immediately upwind, and we will tell you whether a CO₂ unit belongs in the plan at all. You can reach the team through our contact page. The full CO₂ mosquito trap range is listed separately for buyers who already know what they need.