DENVER (KDVR) — Spiders will be creeping into Colorado homes more frequently as the weather starts to cool down this winter.

Spiders can certainly give you the creeps, but most are harmless, other than sending shivers down your spine.

Many spiders can bite, and those bites might cause irritation, but only a couple of species in Colorado are dangerous to humans, according to Colorado State University.

Western black widow

The infamous black widow is the most common type of dangerous spider in Colorado, according to Colorado State University.

Widow spiders are not aggressive and rarely bite. But when they do, it can be painful and potentially dangerous. CSU said the bite most often comes with an immediate prickling pain, but is sometimes unnoticeable.

According to CSU, the spiders produce a toxin in their venom that targets the nervous system. Oftentimes, victims of black widow bites experience muscle and chest pain, along with swelling and redness at the bite site.

That reaction can spread throughout the body and can cause pain in the abdomen and stomach. Other symptoms include nausea, restlessness, anxiety, breathing and speech difficulty, sweating, swelling of the eyelids and a burning sensation in the feet, according to CSU.

Black widows are often found in window wells, crawl spaces, rodent burrows, garage corners and other dark, undisturbed sites near the ground.

You can identify a female black widow by a red or reddish-orange marking on the underside of the otherwise black body. The pattern often resembles an hourglass shape and may appear as two triangles. Males may appear brown and are significantly smaller.

Recluse spider

Recluse spiders are extremely rare in Colorado because of the climate here. Brown recluse spiders occasionally make their way into the Centennial State, however, they rarely survive or establish a population, CSU said.

The bite may feel like a pinprick or it might be unnoticeable, according to CSU. They don’t always release venom when they bite, but when they do, CSU said proteins in the venom are damaging to human cells.

The bite can only cause some irritation, but sometimes it progresses from a blister to a sinking patch and to an irregular lesion, according to CSU.

They often reside in a loose web in dark corners of buildings. CSU said they can be identified if you look into their eyes. Unlike most spiders, recluse spiders only have three pairs of eyes. They are commonly mistaken for funnel web spiders and wolf spiders, as they have a similar brown appearance.

What to do in the case of a bite

If you are bitten by a spider, the Centers for Disease Control and Prevention recommends identifying the spider if possible before washing the bite area with soap and water. Elevation and applying a cold, damp cloth or ice can help to reduce swelling.

If you think you were bitten by a dangerous spider, the CDC advises seeking professional medical attention.