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First Aid 2023

Spider bite: symptoms, what to do (and how to tell if é poisonous)

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Spider bite: symptoms, what to do (and how to tell if é poisonous)
Spider bite: symptoms, what to do (and how to tell if é poisonous)

Spider bites are relatively frequent accidents, but they can cause a lot of stress, especially when there is a suspicion that the spider may be venomous, such as the black widow spider or brown spider for example.

Most of the time, the spider bite is only identified a few hours after it happens, and may not cause any discomfort or lead to mild symptoms, such as swelling or redness of the skin at the bite site, especially when the bite was caused by common, non-poisonous spiders.

However, when a person is bitten by venomous spiders, serious symptoms can appear, such as pain, cramps or abdominal stiffness, tremor, nausea or fever, and it is important to seek the nearest emergency room for the immediate treatment.


Main symptoms

The main symptoms of spider bite are:

  • Small swelling on the skin;
  • Redness at the bite site;
  • Small wound on the skin;
  • Pain or itching at the bite site.

In the case of venomous spiders, symptoms tend to be more intense and include other more serious signs such as blistering of the skin, sweating, difficulty breathing, fever, pain, abdominal cramping or stiffness, nausea or vomiting, for example.

The ideal is to always try to identify the type of spider that caused the bite, as this makes it easier to identify whether it is a potentially poisonous spider. In such cases, if possible, a photograph of the spider should be taken to the hospital to help doctors identify the type of spider, facilitating treatment and speeding recovery.

What to do after the bite

What to do if you are bitten by a spider is:

  1. Wash the bite site with soap and water;
  2. Elevate the limb where the sting is;
  3. Do not tie or squeeze the bite site;
  4. Do not try to suck the poison from the bite;
  5. Place cold compresses or a cloth soaked in cold water at the sting site to relieve pain and swelling.

If there is a suspicion of being bitten by a poisonous spider, you should also go to the hospital immediately to start the appropriate treatment.

How to spot a poisonous spider

There are three main species of venomous spiders in Brazil:

1. Brown Spider


Stings caused by this type of spider are more frequent in the South and Southeast regions of Brazil, such as São Paulo, Paraná or Rio Grande do Sul. The brown spider is a small type of spider that can reach 3 cm in length and its body is grayish brown in color.

Where they are: are more active at night and, therefore, during the day they hide in dark places such as roots, tree bark, behind furniture, in garages, abandoned boxes or bricks, for example.

Symptoms of the bite: initially the spider bite is not felt, but up to 24 hours there is an increasing pain, redness, blisters and swelling in the bite area and also the person may experience fever, malaise and vomiting. After 5 days, it is common for a black crust to appear on the skin, which falls off, 2 to 3 weeks later, causing a wound that must be treated in the hospital.

Special care: keep the area dry and avoid physical activity, as it can help spread the poison throughout the body.

Treatment for brown spider bite

Treatment should be done in the hospital with the injection of serum for brown spider venom. In some cases, especially when more than 24 hours have passed, the doctor may not advise the use of the serum because its effect may not compensate for the risks.

In addition, the scab caused by the spider bite must be removed through surgery to facilitate healing, and on-site treatments must be performed by a nurse at the hospital. In the most severe cases, in which the bite affected a very large region, it may still be necessary to perform a reconstructive surgery of the place.

2. Spider bite


These bites are frequent throughout the Brazilian territory, since it is possible to find this spider throughout South America. However, there is a greater number of cases during the months of March and April in the Southeast of the country, as these are the periods in which the wandering spider is more active.

The wandering spider is usually a large spider with a body of 4 cm, but it can reach 15 cm in length with its legs. Its body is grayish brown or yellowish. This type of spider is known to adopt a defensive position that consists of supporting itself on the last 2 pairs of legs, raising its head and front legs. They can also jump up to 40 cm away.

Where they are: can be found in dark and damp places such as tree bark, fallen logs, banana trees, inside shoes, behind furniture or curtains, for example.

Symptoms of the bite: intense pain appears soon after the bite, accompanied by marks, swelling and redness at the bite site. In addition, increased heart rate, excessive sweating, vomiting, diarrhea, agitation and increased blood pressure may occur.

Treatment for spider bite

Treatment should be done in the hospital by injecting anesthetics at the site of the bite to help reduce the pain that eventually disappears within 3 hours of the accident. Only in cases of more serious symptoms, such as decreased heart rate or shortness of breath, it is necessary to undergo treatment with serum for the venom of this spider.

3. Black widow spider bite


This type of spider is more common near the sea, especially near abandoned beaches, but bites can happen all over Brazil, as the black widow is distributed in tropical and temperate regions.

The black widow is a small type of spider, about 2 cm, that has long, thin legs, as well as a black body with a spot on the belly region, usually red. Although this spider does not attack, it can bite when pressed against the body.

Where they are: remain in damp and dark places and, therefore, can be in places such as bushes, tires, empty cans, shoes and lawns, for example.

Symptoms of the sting: begin with a sharp pain at the sting site, as if with a pin prick, and after 15 minutes the pain turns into a burning sensation which worsens over 48 hours. Symptoms such as nausea, vomiting, muscle pain and increased body temperature are also common.

Treatment for black widow spider bite

Treatment should be started in the hospital as soon as possible with the injection of the specific serum for the spider venom. Usually the symptoms improve up to 3 hours after the beginning of the treatment, but the patient must be hospitalized for 24 hours to see if the symptoms reappear.

Knowing what to do in these kinds of situations is important to save a life. Therefore, learn what to do in case of being bitten by other animals such as snakes or bees.

How to avoid spider bite

To prevent a person from being bitten by a spider, it is important to keep the house and vacant lots clean, as these animals breed and live in dirty and damp places. The accumulation of rubble and construction materials also favors proliferation and, consequently, a person who works and lives close to these places is more likely to be bitten by spiders and even scorpions, so you should avoid letting these products accumulate. Learn more about what to do in case of a scorpion sting.

In addition, people who live in places with infestation of these animals should always shake out their clothes before putting them on and it is also necessary to tap shoes and boots before putting them on, as this avoids the occurrence of bites.

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