[4][5] The documented range of this species lies roughly south of a line from southeastern Nebraska through southern Iowa, Illinois, and Indiana to southwestern Ohio.

[9] From this study, the most common spider submitted from California as a brown recluse was in the genus Titiotus, whose bite is deemed harmless.

A similar study documented that various arachnids were routinely misidentified by physicians, pest control operators, and other non-expert authorities, who told their patients or clients that the spider they had was a brown recluse when in fact it was not.

[12][13] Note that the occurrence of brown recluses in a single building (such as a warehouse) outside of the native range is not considered as successful colonization; such single-building populations can occur (e.g., in several such cases in Florida),[14] but do not spread, and can be easily eradicated.

[19](p 63) The brown recluse will, though not habitually, cannibalize another if food becomes scarce; especially during its typical mating season from June to September or when an unreceptive female encounters an aggressive male.

"[19](p 57) Brown recluse spiders build asymmetrical (irregular) webs that frequently include a shelter consisting of disorderly threads.

They frequently build their webs in woodpiles and sheds, closets, garages, plenum spaces, cellars, and other places that are dry and generally undisturbed.

When dwelling in human residences they seem to favor cardboard, possibly because it mimics the rotting tree bark which they inhabit naturally.

[25][26] The spider usually bites only when pressed against the skin, such as when tangled within clothes, shoes, towels, bedding, inside work gloves, etc.

Many human victims report having been bitten after putting on clothes or shoes that had not been worn recently or had been left for many days undisturbed on the floor.

Rarely, such bites can result in hemolysis, low platelet levels, blood clots throughout the body, organ damage, and even death.

In such instances, the bite forms a necrotizing ulcer as the result of soft tissue destruction and may take months to heal, leaving deep scars.

[7][24][32] Stoecker, Vetter & Dyer (2017) suggested the mnemonic "NOT RECLUSE", shown below, as a memory device to help laymen and medical professionals more objectively screen and diagnose potential cases of loxoscelism.

[7] The most important of these is methicillin-resistant Staphylococcus aureus (MRSA), a bacterium whose necrotic lesions are very similar to those induced by recluse bites, and which can be lethal if left untreated.

[37] Reported cases of brown recluse bites occur primarily in Arkansas, Colorado, Kansas, Missouri, Nebraska, Oklahoma, and Texas.

For example, the venom of the hobo spider, a common European species now established in the northwestern United States and southern British Columbia, has been reported to produce similar symptoms as the brown recluse bite when injected into laboratory rabbits.

If it can be easily captured, the spider should be brought with the patient in a clear, tightly closed container so it may be identified by an arachnologist; if there is no specimen at all, then confirmation by an expert is impossible.

[44] Routine treatment should include immobilization of the affected limb, application of ice, local wound care, and tetanus prophylaxis.

Many other therapies have been used with varying degrees of success, including hyperbaric oxygen, dapsone, antihistamines (e.g., cyproheptadine), antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage, surgical excision, and antivenom.

[7] Outpatient palliative care following discharge often consists of a weak or moderate strength opioid (e.g. codeine or tramadol, respectively) depending on pain scores, an anti-inflammatory agent (e.g. naproxen, cortisone), and an antispasmodic (e.g. cyclobenzaprine, diazepam), for a few days to a week.

[medical citation needed] In presumed cases of recluse bites, dapsone is often used for the treatment of necrosis, but controlled clinical trials have yet to demonstrate efficacy.

[53] Due to increased fear of these spiders prompted by greater public awareness of their presence in recent years, the extermination of domestic brown recluses is performed frequently in the lower midwestern United States.