Missouri is home to a wide range of insects, spiders, and ticks that residents deal with year-round. Some are harmless nuisances, others carry serious diseases, and a few invasive species threaten the state’s forests and crops. Here’s what you’re most likely to encounter and what you should know about each one.
Brown Recluse Spiders
The brown recluse is one of Missouri’s most medically significant spiders, and it’s now presumed to occur statewide indoors. It’s a small spider, with females reaching about an inch long including legs, and has a grayish yellow-brown body with a distinctive violin-shaped marking on its head. The legs are darker than the body and long and slim.
True to its name, the brown recluse hides in undisturbed spots: little-used drawers, closets, attics, basements, behind baseboards, and packed-away clothing. It can’t climb smooth surfaces, so it often turns up trapped in bathtubs and sinks. Outdoors, it lives under rocks and in crevices. The most common scenario for bites is putting on stored clothing or towels without shaking them out first.
Most brown recluse bites produce nothing more than a temporary small red mark. When a more significant reaction occurs, swelling, redness, and tenderness develop within about eight hours, sometimes accompanied by chills, nausea, or fever. In a smaller number of cases, the skin at the bite ulcerates over several days, forming a deep open wound that heals slowly and can persist for months, eventually leaving a sunken scar. Systemic reactions with fever, rash, and dizziness are very rare.
Ticks and Tick-Borne Disease
Missouri ranks among the highest-risk states in the country for tick exposure. Multiple tick-borne diseases are reported here: Rocky Mountain spotted fever, ehrlichiosis, tularemia, Heartland virus, Bourbon virus, and Lyme or a Lyme-like illness. Case numbers have been rising year over year, partly from better reporting but also from environmental changes that increase human exposure.
The lone star tick deserves special attention. Its bite can trigger alpha-gal syndrome, an allergic reaction to a sugar molecule found in red meat, dairy, and mammalian byproducts like gelatin. People who develop it can experience hives, swelling, wheezing, and gastrointestinal symptoms after eating these foods, and in rare cases the reaction can be life-threatening. Missouri has one of the highest rates of alpha-gal antibodies in the country. A large study of adults in tick-heavy states found that 26% of Missouri adults tested positive for these antibodies, trailing only Arkansas among the states surveyed.
Chiggers
Chiggers are tiny mites that thrive in brushy, grassy, or weedy areas that hold moisture during the day. They’re most active on warm afternoons when ground temperatures sit between 77 and 86°F, become inactive below 60°F, and die below 42°F. You’ll rarely see the mites themselves. What you’ll notice are intensely itchy welts, often with a tiny red dot at the center, clustered where skin is thin or where clothing fits tight: ankles, backs of knees, the waistline, crotch, and armpits.
The good news is that North American chiggers don’t carry diseases. The bad news is the itching can be maddening. Unlike ticks and mosquitoes, chiggers are purely a comfort problem, not a health threat.
Stinging Caterpillars
Several species of flannel moth caterpillars in Missouri can deliver a painful sting on contact. The southern flannel moth caterpillar, sometimes called the puss caterpillar, is the most notorious. It looks fuzzy and harmless, but its hair-like spines inject a toxin that can cause intense stinging, burning, rash, swelling, and occasionally fever or nausea. Reactions vary by species and individual sensitivity, but puss caterpillar stings sometimes require medical attention.
If you brush against one, wash the area immediately. Press tape sticky-side down against the skin and peel it off to remove embedded spines, repeating with fresh strips. Ice packs help with swelling, and hydrocortisone cream or a baking soda paste can ease discomfort.
Mosquitoes
Missouri’s warm, humid summers make it prime mosquito territory. Standing water in puddles, ditches, and artificial containers like flowerpot saucers and old tires provides ideal breeding habitat. Mosquitoes here can carry West Nile virus and other pathogens, making them more than just a backyard annoyance. Eliminating standing water around your property is the single most effective step for reducing mosquito numbers near your home.
Invasive Insects Threatening Trees and Crops
Several invasive insects are actively damaging Missouri’s forests or approaching the state’s borders. The emerald ash borer is already present and kills every type of ash tree it infests, including healthy, vigorous ones. Japanese beetles feed on over 300 plant species, with elm, crabapple, sycamore, cherry, birch, rose, and grape among their favorites.
The Asian longhorned beetle could destroy millions of acres of American hardwoods if it spreads further. The spongy moth, an accidental European introduction responsible for millions of dollars in forest damage in the eastern U.S., hasn’t reached Missouri yet but is expected to arrive eventually. The spotted lanternfly, already established in several eastern states, threatens both forests and food crops. Thousand cankers disease targets black walnut trees, which is a particular concern given Missouri’s significant walnut industry.
One of the simplest ways to slow these pests is to avoid moving firewood. Many tree-killing insects travel in logs. If you’re camping, buy firewood locally and burn it all before you leave. You can report suspected invasive tree pests to the Missouri Department of Conservation at forest.health@mdc.mo.gov.
Protecting Yourself Outdoors
For mosquitoes, a repellent with 10% to 35% DEET provides solid protection with a single application. Picaridin, oil of lemon eucalyptus, and IR3535 also work against mosquito bites. Ticks are harder to repel. Only DEET-based products applied to skin are effective against them, and a higher concentration of 20% to 50% is recommended. Adults over 40 or anyone with a weakened immune system should consider using the higher end of that range.
For children over two months old, the American Academy of Pediatrics recommends 10% to 30% DEET. Oil of lemon eucalyptus should not be used on children under three.
If you spend extended time outdoors, permethrin is worth adding to your routine. It’s applied to clothing, shoes, and gear (never skin) and actually kills ticks and mosquitoes on contact with treated fabric. Let it dry completely before wearing treated items. Wearing light-colored, long-sleeved clothing makes ticks easier to spot, and tucking pants into boots with tightly woven socks helps block seed ticks from reaching skin.