Whether or not they notice them, Maine gardeners are constantly surrounded by numerous spiders when working in their yards. Even though nearly every spider species on the planet produces venom, few are dangerous to humans. Individuals with weakened or sensitive immune systems, however, may experience serious reactions from otherwise medically insignificant spider species.

Spider web with dew
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A spider in the center of a web in the dewy grass.

Black Widow

Redback Spider
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A black widow spider crawling up a web near a porch step.

One of the few medically significant spider species in the United States and arguably the most feared, the northern black widow (Latrodectus variolus) is an infrequent inhabitant from southern to mid-Maine. A female shares the shiny, black, globular body and red markings common to other female widow spiders. Unlike the western black widow (Latrodectus hespus) and southern black widow (Latrodectus mactans), however, a northern black widow female's red markings rarely form a complete hourglass shape.

A female black widow spins an irregular, cobweblike web close to the ground. The spider often sits in the center or top of the web upside down while guarding its egg sac. Although the spider is shy, someone accidentally touching its web or getting too close to an egg sac will cause the spider to protect its young by biting.

The bite from a black widow is potentially very serious. The venom is a neurotoxin and causes a set of symptoms known as latrodectism. The toxin enters the nervous system and produces a numbing, achy sensation in the region of the bite. Painful muscle cramping follows, particularly in the bite victim's abdomen. Other symptoms may include nausea, sweating, elevated blood pressure, tremors and vomiting.

Sac Spider

Cheiracanthium punctorium ("Yellow sac Spider")
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A close-up of a yellow sac spider spinning a sac in the grass.

The sac spider of the species Cheiracanthium mildei sometimes produces bites that are medically significant in some individuals. This cream- to yellowish-colored spider may be found in Maine on plants and under debris outdoors. Although nocturnal and rarely seen outdoors, it readily bites when confronted.

The Cheiracanthium mildei sac spider and the agrarian sac spider (Cheiracanthium inclusum) may account for many people's spider bites, according to a Pennsylvania State University Extension fact sheet. The bites seldom cause serious reactions, although individuals sensitive to them may experience a very painful and burning sensation at the bite site and intense itching. Within 10 hours of the bite, the area may have a rash and blister. Systemic reactions may include fever, muscle cramping and nausea.

Large Species

Wolf spider on a leaf
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A close-up of a wolf spider in the sunshine on a leaf.

Several species of spiders in the state bite when their egg sacs are disturbed or they are handled, even when they are handled accidentally. Wolf spiders (Lycosidae) are often large, fast and hairy. Although they usually quickly retreat when confronted, some of the largest wolf spiders produce a painful bite.

Some of the largest web builders in Maine include the 1-inch-long-bodied black and yellow argiope (Argiope aurantia) and banded argiope (Argiope trifasciata). With their legs, these spiders can be several inches long, particularly the females. Despite their large size, argiopes are often docile and timid, and don't bite unless their egg sacs are disturbed.

Fishing spiders (Dolomedes spp.) include Maine's largest native spiders. These spiders often perch on vertical surfaces while waiting for prey. Their legs are normally sprawled, making the spiders appear even larger.

Bite Prevention

Spider trapped in a jar
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A close-up of a spider inside of a jar with a leaf.

In the garden, the best way to prevent spider bites is to be aware of where you place your hands. Because sac and black widow spiders tend to stay out of sight, keeping your ungloved hands where you can see them is especially important. Black widows sometimes build their webs in outbuildings, under porch steps and around water spigots. Stay aware of your surroundings when at those and other locations, and shake out your garden gloves before putting them on your hands.

If you are bitten by a spider and fear it is a dangerous species, then carefully and safely collect the spider in a jar or other container for its positive identification. Wash the bite wound with mild soap and water, and then place a clean, cool compress over the bite to reduce swelling. An over-the-counter medication such as acetaminophen or ibuprofen can help alleviate pain; an antihistamine can help reduce itching, swelling and other symptoms. Seek immediate medical attention if symptoms are severe or linger, or if you have additional symptoms.