Reliable diagnoses of spider bites require three conditions: first, there should be clinical effects of the bite at the time or soon afterwards, although there are no symptoms universally diagnostic of a spider bite, and bites by some spiders, e.g. "Loxosceles" species, may initially be painless; second, the spider should be collected, either at the time of the bite or immediately afterwards; and third, the spider should be identified by an expert arachnologist.

Spider bites are commonly misdiagnosed. A review published in 2016 showed that 78% of 134 published medical case studies of supposed spider bites did not meet the necessary criteria for a spider bite to be verified. In the case of the two genera with the highest reported number of bites, "Loxosceles" and "Latrodectus", spider bites were not verified in over 90% of the reports. Even when verification had occurred, details of the treatment and its effects were often lacking. Unverified bite reports likely represent many other conditions, both infectious and non-infectious, which can be confused with spider bites. Many of these conditions are far more common and more likely to be the source of necrotic wounds. An affected person may think that a wound is a spider bite when it is actually an infection with methicillin-resistant "Staphylococcus aureus" (MRSA). False reports of spider bites in some cases have led to misdiagnosis and mistreatment, with potentially life-threatening consequences.

A definitive diagnosis of health effects due to bed bugs requires a search for and finding of the insect in the sleeping environment as symptoms are not sufficiently specific. Other possible conditions with which these conditions can be confused include scabies, allergic reactions, mosquito bites, spider bites, chicken pox and bacterial skin infections. Bed bugs classically form a line of bites colloquially referred to as "breakfast, lunch, and dinner" and rarely feed in the armpit or behind the knee which may help differentiate it from other biting insects. If the number in a house is large a pungent sweet odor may be described.

Cat bites can often be prevented by:

- instructing children not to tease cats or other pets.

- being cautious with unfamiliar cats.

- approaching cats with care, even if they appear to be friendly.

- avoiding rough play with cats and kittens.

Rough play causes is perceived as aggressive. This will lead to the cat being defensive when approached by people. Preventing cat bites includes not provoking the cat.

Estimating the number of spider bites that occur is difficult as the spider involvement may not be confirmed or identified. Several researchers recommend only evaluating verified bites: those that have an eyewitness to the bite, the spider is brought in, and identified by expert. With "suspected arachnidism" the diagnosis came without a spider positively identified.

The diagnosis is aided by obtaining a history of the circumstances surrounding the bite. The time the bite was experienced, the location of the bite, and examination of the bite is noted. The person may have drainage from the site of the bite. They may also be febrile. Swelling may also occur. Because the wound from the bite may have healed over the punctures, the wound it may be opened and explored. The site is anesthetized prior to exploration of the wound for is examined for damage. Neurovascular status is assessed. Immune status may determine treatment as does

the presence of transplanted tissue or organs, rheumatic disease, diabetes, HIV/AIDS and sickle cell disease.

Swollen glands (lymph nodes) and red streaks radiating upward may be evident.

The diagnosis of a cat with rabies is evident by observing the cat. Cats with rabies may also appear restless, pant, and attack other animals, people, or objects. Animals with rabies typically die within a few days of appearing sick. Vaccination of the cat can prevent rabies being transmitted by the cat through a bite. If the cat is suspected of being infected with rabies, the person begins treatment with rabies vaccine.

The spider biting apparatus is short and bites are only possible in experimental animals with pressure on the spider's back. Thus many bites occur when a spider is trapped in a shirt or pant sleeve. There is no commercial chemical test to determine if the venom is from a brown recluse. The bite itself is not usually painful. Many necrotic lesions are erroneously attributed to the bite of the brown recluse. (See Note). Skin wounds are common and infections will lead to necrotic wounds. Thus many terrible skin infections are attributed falsely to the brown recluse. Many suspected bites occurred in areas outside of its natural habitat. A wound found one week later may be misattributed to the spider. The diagnosis is further complicated by the fact that no attempt is made to positively identify the suspected spider. Because of this, other, non-necrotic species are frequently mistakenly identified as a brown recluse. Several certified arachnologists are able to positively identify a brown recluse specimen on request.

Reports of presumptive brown recluse spider bites reinforce improbable diagnoses in regions of North America where the spider is not endemic such as Florida, Pennsylvania, and California.

A new mnemonic device, "NOT RECLUSE", has been suggested as a tool to help professionals more objectively exclude skin lesions that were suspected to be loxosceles.

Numerous, Occurrence( wrong geography) Timing( wrong season), Red Center, Elevated, Chronic, Large (more than 10 cm), Ulcerates too quickly (less than a week), Swollen, Exudative

There are no tests required to diagnose widow spider bites, or latrodectism symptoms. The diagnosis is clinical and based on historic evidence of widow spider bites. Pathognomonic symptoms such as localized sweating and piloerection provide evidence of envenomation. Unlike the brown recluse, the widow species are easily identified by most people.

Diagnosis is obvious in most people reporting contact with a "Latrodectus" spider. However, without a spider, either through inability to communicate or unawareness, the diagnosis may be missed as symptoms overlap with a variety of other serious clinical syndromes such as tetanus or acute abdomen. Blood values are typically unimportant but may be needed to show myocarditis or dehydration from vomiting.

Identification of the snake is important in planning treatment in certain areas of the world, but is not always possible. Ideally the dead snake would be brought in with the person, but in areas where snake bite is more common, local knowledge may be sufficient to recognize the snake. However, in regions where polyvalent antivenoms are available, such as North America, identification of snake is not a high priority item. Attempting to catch or kill the offending snake also puts one at risk for re-envenomation or creating a second person bitten, and generally is not recommended.

The three types of venomous snakes that cause the majority of major clinical problems are vipers, kraits, and cobras. Knowledge of what species are present locally can be crucial, as is knowledge of typical signs and symptoms of envenomation by each type of snake. A scoring system can be used to try to determine the biting snake based on clinical features, but these scoring systems are extremely specific to particular geographical areas.

It is not an easy task determining whether or not a bite by any species of snake is life-threatening. A bite by a North American copperhead on the ankle is usually a moderate injury to a healthy adult, but a bite to a child's abdomen or face by the same snake may be fatal. The outcome of all snakebites depends on a multitude of factors: the size, physical condition, and temperature of the snake, the age and physical condition of the person, the area and tissue bitten (e.g., foot, torso, vein or muscle), the amount of venom injected, the time it takes for the person to find treatment, and finally the quality of that treatment.

Anti-venoms are commercially prepared antibodies to toxins in animal bites. They are specific for each bite. There are several anti-venoms commercially available in Brazil, which have been shown to be effective in controlling the spread of necrosis in rabbits. When administered immediately, they can almost entirely neutralize any ill effects. If too much time is allowed to pass, the treatment becomes ineffective. Most victims do not seek medical attention within the first twelve hours of being bitten, and these anti-venoms are largely ineffective after this point. Because of this, anti-venoms are not being developed more widely. They have, however, been proven to be very effective if administered in a timely manner and could be utilized in Brazil as a legitimate technique.

Treatment requires keeping the person from being repeatedly bitten and possible symptomatic use of antihistamines and corticosteroids (either topically or systemically). There however is no evidence that medications improve outcomes and symptoms usually resolve without treatment in 1–2 weeks.

Avoiding repeated bites can be difficult, since it usually requires eradicating bed bugs from a home or workplace; eradication frequently requires a combination of pesticide and non pesticide approaches. Pesticides that have historically been found to be effective include pyrethroids, dichlorvos and malathion. Resistance to pesticides has increased significantly over time and there are concerns of negative health effects from their usage. Mechanical approaches such as vacuuming up the insects and heat treating or wrapping mattresses have been recommended.

"Bartonella" growth rates improve when cultured in an enrichment inoculation step in a liquid insect-based medium such as "Bartonella" α-Proteobacteria Growth Medium (BAPGM) or Schneider’s Drosophila-based insect powder medium. Several studies have optimized the growing conditions of "Bartonella" spp. cultures in these liquid media, with no change in bacterial protein expressions or host interactions "in vitro". Insect-based liquid media supports the growth and co-culturing of at least seven "Bartonella" species, reduces bacterial culturing time and facilitates PCR detection and isolation of "Bartonella" spp. from animal and patient samples. Research shows that DNA may be detected following direct extraction from blood samples and become negative following enrichment culture, thus PCR is recommended after direct sample extraction and also following incubation in enrichment culture. Several studies have successfully optimized sensitivity and specificity by using PCR amplification (pre-enrichment PCR) and enrichment culturing of blood draw samples, followed by PCR (post-enrichment PCR) and DNA sequence identification.

As "Bartonella" spp. infect at low levels and cycle between blood and tissues, multiple blood draws over time may be necessary to detect infection.

Diagnosis is based on a combination of clinical features and biopsy.

The aim of treatment is to relieve the allergy-induced itch and to remove the fleas from the pet and its home environment. In some cases, secondary bacterial or yeast infections will also need treatment before the itching subsides. Environmental flea control includes using flea foggers or bombs, vacuuming, and treating pet bedding by washing on a hot cycle (over 60 degrees Celsius) in the washing machine. The current on-pet treatment recommended by veterinary dermatologists is spinosad (Comfortis) monthly and nitenpyram (Capstar or generics) every 48 hours until improvement.

Many pets with FAD may also have other allergies, such as allergies to food, contact allergies, and atopic dermatitis.

The vast majority of victims fully recover without significant lasting problems (sequelae). Death from latrodectism is reported as high as 5% to as low as 0.2%. In the United States, where antivenom is rarely used, there have been no deaths reported for decades.

Despite frequent reference to youth and old age being a predisposing factor it has been demonstrated that young children appear to be at lowest risk for a serious bite, perhaps owing to the rapid use of antivenom. Bite victims who are very young, old, hypotensive, pregnant or who have existing heart problems are reported to be the most likely to suffer complications. However, due to the low incidence of complications these generalizations simply refer to special complications (see Special circumstances).

Cat-scratch disease is characterized by granulomatous inflammation on histological examination of the lymph nodes. Under the microscope, the skin lesion demonstrates a circumscribed focus of necrosis, surround by histiocytes, often accompanied by multinucleated giant cells, lymphocytes, and eosinophils. The regional lymph nodes demonstrate follicular hyperplasia with central stellate necrosis with neutrophils, surrounded by palisading histiocytes (suppurative granulomas) and sinuses packed with monocytoid B cells, usually without perifollicular and intrafollicular epithelioid cells. This pattern, although typical, is only present in a minority of cases.

The diagnosis of flea allergy dermatitis is complicated by the grooming habits of pets. Cats in particular are very efficient at grooming out fleas, often removing any evidence of infestation. Fleas begin biting within 5 minutes of finding a host, and there are no flea treatments that kill fleas before biting occurs.

There are no diagnostic tests for tungiasis. This is most likely because the parasite is ectoparasitic with visible symptoms. Identification of the parasite through removal, and a patient’s traveling history, should suffice for diagnosis, though the latter is clearly more useful than the former. Localization of the lesion may be a useful diagnostic method for the clinician. A biopsy may be done, though again, it is not required for diagnosis.

Pulicosis (also known as "flea bites") is a skin condition caused by several species of fleas, including the cat flea ("Ctenocephalides felis") and dog flea ("Ctenocephalides canis"). This condition can range from mild irritation to severe irritation. In some cases, 48 to 72 hours after being bitten, a more severe rash-like irritation may begin to spread across the body. Symptoms include swelling of the bitten area, erythema, ulcers of the mouth and throat, restlessness, and soreness of the areolae. In extreme cases, within 1 week after being bitten, the condition may spread through the lymph nodes and begin affecting the central nervous system. Permanent nerve damage can occur.

If they receive an excessive number of bites, pets can also develop flea allergy dermatitis, which can potentially be fatal if no actions are taken. However, dogs and cats are not the only ones that are at risk. Humans can suffer from flea bites and, depending on a variety of factors, the bites can cause much pain and discomfort.

The Warthin–Starry stain can be helpful to show the presence of "B. henselae", but is often difficult to interpret. "B. henselae" is difficult to culture and can take 2–6 weeks to incubate. The best diagnostic method currently available is polymerase chain reaction, which has a sensitivity of 43-76% and a specificity (in one study) of 100%.

Chiggers are commonly found on the tip of blades of grasses to catch a host, so keeping grass short, and removing brush and wood debris where potential mite hosts may live, can limit their impact on an area. Sunlight that penetrates the grass will make the lawn drier and make it less favorable for chigger survival.

Chiggers seem to affect warm covered areas of the body more than drier areas. Thus, the bites are often clustered behind the knees, or beneath tight undergarments such as socks, underwear, or brassieres. Areas higher in the body (chest, back, waist-band, and under-arms) are affected more easily in small children than in adults, since children are shorter and are more likely than adults to come in contact with low-lying vegetation and dry grass where chiggers thrive. An exceptional case has been described in the eye, producing conjunctivitis.

Application of repellent to the shoes, lower trousers and skin is also useful. Because they are found in grass, staying on trails, roads, or paths can prevent contact. Dusting sulfur is used commercially for mite control and can be used to control chiggers in yards. The dusting of shoes, socks and trouser legs with sulfur can be highly effective in repelling chiggers.

Another good strategy is to recognize the chigger habitat to avoid exposure in the first place. Chiggers in North America thrive late in summer, in dry tall grasses and other thick, unshaded vegetation. Insect repellents containing one of the following active ingredients are recommended: DEET, catnip oil extract (nepetalactone), citronella oil or eucalyptus oil extract. However, in 1993 issue a study reported on tests of two commercial repellents: DEET and citrus oil: "All chiggers exposed on the filter papers treated with DEET died and did not move off the treated papers. None of the chiggers that were placed on papers treated with citrus oil were killed." It was concluded that DEET was more effective than citrus oil.

Chiggers can also be treated using common household vinegar (5% acetic acid).

Many species of arthropods (insects, arachnids and others) regularly or occasionally bite or sting human beings. Insect saliva contains anticoagulants and enzymes that cause local irritation and allergic reactions. Insect venoms can be delivered by their stingers, which often are modified ovipositors, or by their mouthparts. Insect, spider and scorpion venom can cause serious injury or death. Dipterans account for the majority of insect bites, while hymenopterans account for the majority of stings. Among arachnids spider bites are the most common. Arthropods bite or sting humans for a number of reasons including feeding or defense. Arthropods are major vectors of human disease, with the pathogens typically transmitted by bites.

The histomorphologic appearance of insect bites is usually characterized by a wedge-shaped superficial dermal perivascular infiltrate consisting of abundant lymphocytes and scattered eosinophils. This appearance is non-specific, i.e. it may be seen in a number of conditions including:

- Drug reactions,

- Urticarial reactions,

- Prevesicular early stage of bullous pemphigoid, and

- HIV related dermatoses.

This condition is diagnosed by detecting the bacteria in skin, blood, joint fluid, or lymph nodes. Blood antibody tests may also be used. To get a proper diagnosis for rat-bite fever, different tests are run depending on the symptoms being experienced.

To diagnosis streptobacillary rat-bite fever, blood or joint fluid is extracted and the organisms living in it are cultured. Diagnosis for spirillary rat bite fever is by direct visualization or culture of spirilla from blood smears or tissue from lesions or lymph nodes. Treatment with antibiotics is the same for both types of infection. The condition responds to penicillin, and where allergies to it occur, erythromycin or tetracyclines are used.