Black Widow Spiders- Friend or Foe?

Jesse Fulbright, MSU Liberty County Extension

Almost everyone finds the children’s book, “Charlotte’s Web,” endearing, with its spider heroine.  In real life though, very few people, it seems, enjoy spiders.  While I love bugs, I too am not a huge fan of spiders.  They fascinate me at a distance.  However, a couple of weeks ago at the fair, I had the opportunity to capture a black widow spider to remove it and other people from harm’s way.  So, let’s talk about the black widow spider a bit more because it is the only poisonous spider found in Montana, without being transported in by some means.

The black widow spider is easily recognized by the hourglass marking on the underside of the abdomen.  This marking is reddish or orange on live specimens, but loses its color when preserved in alcohol.  Black widow spiders get their name from the fact that the female frequently eats the male after mating, a practice not uncommon to several other species of spiders.

There are at least two species of black widow spiders in Montana, the northern black widow and the western black widow.  They are distinguishable by their color markings.

The western black widow female has a complete hourglass marking on the underside of the abdomen, which is usually completely black except for a small reddish spot near the tip.  Males of the western black widow are usually light brown.

The northern black widow spider is similar to the western black widow except the hourglass marking on the underside of the abdomen is incomplete or split into two triangles.  The abdomen of the female is black with a row of reddish spots along the top and diagonal whitish bands on each side.  

The bite of both the western and northern black widow is a neurotoxin and is very painful.  The pain occurs less at the actual bite but rather in the abdomen and limbs.  Physiological effects are an accelerated heartbeat, increased blood pressure, breathing difficulties, and paralysis.  When death occurs, it is due to suffocation.  Although the bite of a black widow is rarely fatal it is important to seek medical attention.  Antidotes are commercially available.

Spiders are beneficial, preying on insects, so control measures should only be used in situations where they become intolerable – for instance, where black widow or other spiders pose a threat to individuals or pets.  A broom or vacuum cleaner used to dislodge and move outside or crush spiders will suffice.  Keeping debris and wood piles away from living quarters will aid in limiting food sources and spider havens.  Spiders are often found outside under eaves and in corners of residences.  By carefully manipulating a broom, one can remove the spiders and relocate them away from the house.