No-see-um bites usually show up as small red welts, about 1/8 inch across, or water-filled blisters that itch intensely. They come from biting midges so small you rarely see them, active at dawn and dusk near water. A repellent with a listed active, plus light long sleeves, keeps the evening going.
Once you know what you are dealing with, it gets easier to stay on the dock, the beach or the porch for the best part of the day.
What are no-see-ums?
If you have ever come in from a golden-hour walk with fresh, itchy bites and no idea what made them, you are in good company. University of Arizona Extension notes that people often see only the bites and wonder what bit them. Sometimes they notice small insects flying around but never see them biting.
These are usually small biting midges called no-see-ums, also known as punkies or sand flies. They belong to the genus Culicoides and the family Ceratopogonidae, in the same insect order (Diptera) as mosquitoes. For where they breed, when they bite and how to keep them off your porch, see our complete guide to no-see-ums.
Why you cannot see them
According to University of Arizona Extension, adults are small, dark flies about 1/8 to 1/4 inch long and barely visible to the naked eye. They have short, stocky bodies and a shiny thorax, and up close they look like miniature mosquitoes.
Who actually bites
Only adult females need blood, which they use to produce eggs. Both males and females feed on pollen and nectar, so the males are not a biting concern.
There are a lot of them, too. University of Florida entomologists count over 4,000 species of biting midges worldwide, over 1,000 of them in Culicoides, and 47 species in Florida alone.
What do no-see-um bites look like?
University of Arizona Extension describes the bites as usually appearing "as small red welts (about 1/8th inch in diameter) or water-filled blisters, that itch intensely."
A few more details from the same source:
- Welts or blisters can break open and bleed when scratched, and the itching may continue.
- Sensitive people may develop long-lasting painful and itchy lesions.
- Bites may come with allergic reactions.
University of Florida entomologists describe the bites as "irritating, painful, and can cause long-lasting painful lesions for some people." In the US, they note, biting midges are primarily a nuisance, and the main medical issue is an allergic reaction to the bites.
Because the insects are so hard to spot, timing and setting are often your best clues.
No-see-um bites vs mosquito bites vs bed bug bites
Most comparison charts online come from pest-control or product blogs. This one uses only public-agency and university sources: University of Arizona Extension and UF/IFAS Extension for no-see-ums, the CDC mosquito bite page for mosquitoes, and the CDC bed bug FAQ for bed bugs.
| No-see-um | Mosquito | Bed bug | |
|---|---|---|---|
| The insect | Small dark fly, 1/8 to 1/4 inch, barely visible; looks like a miniature mosquito up close (Arizona) | Same insect order as no-see-ums (Arizona) | Hides in mattress and sheet folds (CDC) |
| When you get bitten | Outdoors in early morning and evening, and on calm, cloudy days (UF) | Not covered on the CDC bite page | While you sleep (CDC) |
| How the bite usually looks | Small red welts about 1/8 inch, or water-filled blisters, intensely itchy (Arizona) | Puffy, reddish bump; later a hard, itchy, reddish-brown bump; sometimes small blisters or dark bruise-like spots (CDC) | Ranges from no visible sign, to a small mark, to a serious allergic reaction (CDC) |
| When you notice it | Often after the fact; the insects usually go unnoticed (Arizona) | The puffy bump appears within minutes; the harder bump about a day later (CDC) | Most people notice marks one to several days after the bite (CDC) |
| Other clues | You were near water: beaches, marshes, lake shores, damp ground (Arizona, UF) | None listed on the CDC bite page | Shed skins, rust-colored spots on mattresses or nearby furniture, a sweet musty odor (CDC) |
Bites can look alike, and no chart can tell you for sure what bit you. If you are unsure, ask a pharmacist or doctor.
How long do no-see-um bites last?
This is one of the most searched questions, and the honest answer is that the sources we trust do not give a fixed number of days.
What they do say:
- University of Arizona Extension notes that the itching may continue, and that sensitive people may develop long-lasting painful and itchy lesions.
- University of Florida entomologists say the bites can cause long-lasting painful lesions for some people.
For relief, University of Arizona Extension says over-the-counter topical cortisone creams usually relieve itching, and that for more severe reactions, medical help may be needed from a dermatologist or physician.
Since nobody can promise a timeline, the bigger win is getting fewer bites in the first place.
Where no-see-ums live, and why you keep getting bitten
Near water, almost anywhere
University of Arizona Extension says no-see-ums turn up in almost any habitat near water: springs, ponds, lakes, river banks, beaches and swamps, plus plains and mountains. UF/IFAS Extension adds that their larvae live around salt marsh and mangrove swamps, the shores of streams and ponds, and muddy ground, and that "coastal areas provide primary habitat for biting midges." They do not establish inside homes.
That coastal habit is why they come up so often in our Florida bug spray guide, and why they are worth a thought when you pack for a warm-weather trip like the one in our Costa Rica travel guide.
Year-round in warm places
They are seen in the largest numbers in summer, but University of Arizona Extension notes that in places with warm winters they can occur year-round. They are usually active at dawn or dusk, which happens to be exactly when the light is best.
Your own backyard may be the source
In urban areas, University of Arizona Extension says no-see-ums breed in any muddy or moist spot, including:
- over-irrigated mulch or sod
- tree holes
- new construction sites
- indoor plant pots
- water from air conditioners
- splash pads that drain poorly and collect water
Females may disperse a little over a mile, but high numbers of bites are likely very close to where they emerge. So if you keep getting bitten in the same spot, the source may be a few steps away. The Extension's advice: if bites are high, hold off on irrigation nearby and let moist spots drain and dry.
How to stop no-see-um bites
Use a repellent, and follow the label
University of Arizona Extension puts it simply: "Repellents effective against mosquitos are effective against biting midges." Choose a suitable repellent and always follow the label.
For the actives, the CDC lists these for EPA-registered insect repellents, framed for preventing mosquito bites:
- DEET
- picaridin (called icaridin outside the US)
- IR3535
- oil of lemon eucalyptus (OLE), plant-derived
- para-menthane-diol (PMD)
- 2-undecanone, plant-derived
Put it on every bit of skin you leave uncovered, since these insects are small enough to find any gap. For a closer look at which formulas suit a no-see-um evening, see our guide to the best bug spray for no-see-ums.
Dress for the evening
University of Arizona Extension suggests light colored long-sleeved shirts, pants, shoes and socks, plus hats with fine mesh netting over the face and neck where they are heavy.
Check your screens
No-see-ums can pass through ordinary insect screens and will occasionally bite people indoors. Standard 16 x 16 or 18 x 16 mesh lets them through. University of Arizona Extension recommends replacing it with smaller 30 x 30 mesh where possible, keeping doors and windows screened and shut, not propping doors open, and repairing rips. UF/IFAS Extension notes that finer mesh does limit airflow, so it is a trade-off.
Turn on a fan
Here is a small, satisfying trick. Because biting midges are small and weak fliers, UF/IFAS Extension says ceiling and window fans on high can keep them out of small areas, like a screened porch or a patio table. The same source notes that spraying for adult midges is not efficient, because new ones keep arriving from breeding sites.
A 5-minute setup for a bite-free evening
Pulling the sources together, here is the routine we use before heading out for golden hour:
- Walk the patio. Look for soggy mulch, a puddle under the air conditioner, or a splash pad that has not drained. Skip watering near where you sit, and let damp spots dry.
- Check the screens. Close the doors, look for rips, and note any standard mesh you might upgrade to 30 x 30 later.
- Fan on high. Point a ceiling, box or window fan across the seating area.
- Change into light layers. Long sleeves, light pants, socks and shoes.
- Repellent before the sun drops. Apply to any uncovered skin, following the label.
Then sit back. The whole point is to stay for the sunset, not to retreat indoors at the first itch.
Our pick for beach and porch evenings
We built Bloc Off Spray for exactly these hours. It uses 8% plant-based PMD (para-menthane-3,8-diol) derived from lemon eucalyptus, and on our product page it carries 6+ hours of lab-tested protection against mosquitoes, ticks and other biting insects. It is DEET-free and alcohol-free, with aloe vera and chamomile, in a 4 oz (118 ml) bottle for $15.00.
My co-founder and formulator, Cassidy Huang, and I spent two years with a Taiwan-based chemist developing it. We also added shiso (perilla), which gives the formula a gentle feel and a clean herbal scent. The protection comes from the PMD.
For the beach bag, Bloc Off Wipes come as 10 individually wrapped wipes for $13.00. Not sure which format fits your evening? Our wipes vs spray comparison walks through it.
FAQ
Do no-see-ums bite?
Yes, but only the adult females. According to University of Arizona Extension, females need blood to produce eggs, while both males and females feed on pollen and nectar. Males are not a biting concern.
Why do I keep getting no-see-um bites?
Most likely you are close to where they breed. University of Arizona Extension says they breed in muddy or moist spots, including over-irrigated mulch or sod, plant pots and poorly draining splash pads. High numbers of bites are likely very close to where they emerge. In places with warm winters, they can be around year-round.
How long do no-see-um bites last?
The sources we rely on give no fixed number of days. University of Arizona Extension notes the itching may continue, and both Arizona and University of Florida entomologists say some people develop long-lasting lesions.
Can no-see-ums bite through window screens?
They can get through them. University of Arizona Extension says standard 16 x 16 and 18 x 16 mesh lets no-see-ums pass, and they occasionally bite people indoors. It recommends 30 x 30 mesh where possible, plus keeping doors and windows screened and shut.
Are no-see-ums the same as sand flies?
It depends on where you are. University of Arizona Extension lists "sand flies" as one common name for no-see-ums, while University of Florida entomologists say biting midges are "sometimes incorrectly referred to as sand flies," since true sand flies are a different group. In Australia, "sandflies" usually means biting midges, which we cover in our guide to sandflies in Australia.
Written by Tanya Lee, Co-Founder of The Superbloc. Sources: University of Arizona Cooperative Extension, "Something's biting me, but I can't see it!" (Nair, Gouge, Li, Arizona Pest Management Center, 2018); UF/IFAS Extension EENY 349, "Biting midges, no-see-ums Culicoides spp." (Connelly, revised 2013); CDC, mosquito bite symptoms; CDC, bed bugs FAQ; CDC, mosquito bite prevention (repellent actives).