Straw Itch Mite

What it does

Straw itch mites are parasites of the larvae of grain and wood-boring insects. Females paralyze host larvae, feed, and give birth to fully developed offspring. When their insect hosts are abundant in stored straw, hay, grain, or seeds, mite numbers surge, and people who contact the material get bitten as incidental targets.

Where it lives

They live in stored and field hay, straw, grain, dried beans, seeds, and grasses, wherever their stored-product insect hosts occur. They are found nationwide, most notably in agricultural areas, barns, and homes that bring in infested straw, mattresses, or grain. They do not colonize the home itself.

How it breeds

Reproduction is exceptionally fast. Females carry developing young internally and give birth to mature adults, so a population can multiply enormously in a short time when host larvae are plentiful. Numbers crash once the host insects or the infested material are removed, and the mites cannot sustain themselves on people.

What it eats

The mites feed on the body fluids of insect larvae infesting grain, straw, seeds, and wood. They do not feed on human blood; bites on people are defensive or incidental and do not nourish them.

Identification

Individual mites are about 0.2 mm and effectively invisible to the naked eye, so the bites are usually noticed before the mite. Diagnosis is based on the itchy rash plus a history of contact with hay, straw, grain, or seeds. Microscopy is needed to see the pale, elongated, engorged females.

Signs of an infestation

• Sudden intensely itchy welts after handling straw, hay, or grain
• Rash on the arms, neck, and trunk where material contacted skin
• Small red bumps sometimes topped with a tiny blister
• Multiple people or animals itching after the same exposure
• No visible mite despite obvious bites

Prevention tips

• Wear long sleeves and gloves when handling hay, straw, or grain
• Store grain and seed in sealed containers to limit host insects
• Remove or discard infested straw, hay, and seed sources
• Launder and shower promptly after working with stored plant material
• Control stored-product insects that the mites feed on

Professional solutions

Straw itch mite outbreaks are usually solved by removing the infested material rather than by treating a structure. If stored-product insects are the underlying source, a pest professional can treat and manage that infestation, which removes the mites' food supply. Insecticidal treatment of people is not appropriate; medical care manages the rash.