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How to identify it
- Too small to see without magnification: about 0.2 mm long. SDSU gives about 0.16 mm for males and 0.22 mm for unfed females.[3][1]
- After feeding on an insect host, a female's abdomen swells and she can reach 2.0 mm long.[1]
- Under magnification the front pair of legs points forward, and females have needle-like mouthparts for piercing hosts and injecting venom.[1]
- You usually know them by the bites rather than the mites: intensely itchy red welts, often overlapping and with a small fluid-filled blister in the center, on skin that touched hay, straw or grain. Unlike some other biting mites, no mite is found in the middle of the bite.[1][3]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Flea bites | The Bohart Museum describes straw itch mite bites as itchy red lumps resembling flea bites. Straw itch mite bites show up 11 to 18 hours after contact, on the parts of the body that touched hay, straw or grain, and the mites do not stay on the skin.[3] |
| Pyemotes ventricosus | A related mite that older publications wrongly called the straw itch mite because its bites and skin reactions are similar. It preys on wood-boring beetle larvae, carpet beetles and some insect colonies.[1] |
Where it lives
Found worldwide. Problems come with infested material: SDSU reports that nearly all the cases it hears about in South Dakota come from handling contaminated hay, and NC State gets calls every fall from people who handled or sat on straw bales used for decorations, hay rides or covering new lawns.[1][2]
Biology and life cycle
Straw itch mites are predators and parasites of insects that infest stored grain and dried plant material, including Indian meal moth caterpillars, wheat stem maggots and tumbling flower beetle larvae, so they are considered beneficial.[1][3][2]
They breed in stored grain, dried beans and peas, wheat straw, hay, brome seed and other dried grasses. Their numbers follow the insects they feed on, so a mite problem usually means the material had an insect infestation first. SDSU notes that in a 1950 outbreak, storing new grain on top of old boosted Angoumois grain moths and made attacks on people worse.[2][3][1]
A female attaches to an insect, paralyzes it with a venom strong enough to paralyze insects 166,000 times her size, and feeds on its blood (hemolymph) until her abdomen swells. Her eggs develop all the way to adults inside her, and she gives birth to live young that mate as soon as they emerge.[1]
It takes about four days from mating to birth. Females average 43 offspring per birth, fewer than one in ten of them males, and keep producing young for about 15 days on average (4 to 33 days), so populations can build very quickly when prey is plentiful.[1]
Only the females have venom, and they are the ones that bite.[1]
Damage and signs
- Straw itch mites feed on the insects in hay, straw and grain, which is why they are considered beneficial there. The trouble is their bites on people and animals that come in contact with the infested material.[3][2]
- Livestock can be bitten too. SDSU cites a report of bites on the neck and back of a horse fed contaminated straw.[1]
Health risk
Female mites bite anyone who handles, carries or sits on infested hay, straw or grain. Bites form intensely itchy red welts, often with a small blister in the center, on the arms, chest, back, neck and waist where the material touched the skin, and the rash usually appears 11 to 18 hours after contact; some people report mild fever. The mites do not feed on people or stay on the skin, and there is no evidence they transmit disease, but sensitive people can have severe skin reactions. The Bohart Museum notes that oral antihistamines and topical anti-itch creams can be used to treat the bites.[1][2][3]
Control
Prevention
There is no way to tell whether hay or straw carries the mites before you buy it, so protect yourself when handling bales or stored grain. SDSU reports that DEET repellents greatly reduce or prevent bites, citing a study in which a DEET product prevented all bites, and NC State suggests applying repellent to shirts, pants and arms.[1][2]
For hay rides and displays, NC State suggests a plastic tarp over the bales before anyone sits on them, which may help somewhat.[2]
Sanitation
The best long-term fix is to get rid of the infested material, or at least the insects the mites live on, and to clean storage areas thoroughly.[3][2]
Traps and physical control
In South Dakota, letting infested material freeze often reduces mite numbers, and research has also used heat or sulfur to cut infestations.[1]
Pesticides
Treating bales is hard. Few products are labeled for it, sprays of soapy water or horticultural oil are off-label, and the mites live deep inside the bales, so surface treatments do not reach them. Cleaned storage areas can be treated with a labeled pesticide (NC State names cyfluthrin), which helps but is unlikely to stop the problem entirely.[2][3]
When to call a professional
Stored grain and similar commodities can be fumigated to kill both the mites and their host insects, but only licensed pest control professionals should do it.[2][3]
Common questions
- Why did I get itchy bumps after a hay ride or handling straw bales?
- Straw itch mites in the bales are a common cause, especially in fall when bales are used for decorations, hay rides and covering newly seeded lawns. The bites show up on the arms, trunk and other skin that touched the straw, usually 11 to 18 hours later.[2][3]
- Do straw itch mites live on people?
- No. They bite but do not feed on humans or stay on the skin. They live in the infested hay, straw or grain and on the insects in it, so getting rid of that material is the best fix.[3]
- Do straw itch mites spread disease?
- The Bohart Museum notes there is no evidence that they transmit any pathogens, though the bites can cause severe skin reactions in sensitive people and some people report mild fever.[3][1]
Sources
- South Dakota State University Extension, “Straw Itch Mites, P-00402 (A.J. Varenhorst, P. Wagner, P. Rozeboom; July 2026).” extension.sdstate.edu/sites/default/files/2026-07/P-00402.pdf (accessed 2026-11-08)
- NC State Extension, Department of Entomology and Plant Pathology, “Itch Mite Problems (M. Waldvogel, October 2015).” entomology.ces.ncsu.edu/2015/10/itch-mite-problems/ (accessed 2026-11-08)
- Bohart Museum of Entomology, University of California, Davis, “Straw or Hay Itch Mites, Information No. 043.” bohart.ucdavis.edu/sites/g/files/dgvnsk4616/files/media/documents/note_43_hay_itch_mites.pdf (accessed 2026-11-08)
- iNaturalist, “Pyemotes tritici taxon page (order and family).” www.inaturalist.org/taxa/396112 (accessed 2026-11-08)