Birds Make Good Neighbors

Micrathena gracilis is a spider in the family Araneidae, commonly known as the Spined Micrathena. The dark-spotted, whitish abdomen surrounded by 5 pairs of black-tipped spines distinguishes the female of this common woodland spider.

I’ve followed this spider, daily, since July 10th, 2009. I assume it’s a female (the black tipped spines mentioned earlier), as males do not construct webs after attaining sexual maturity. Reading about this particular spider, and not much information is to be found, these spiders are known to be found in woodland and dense forest areas. However, this little lady has taken up residence on our front porch, connecting her web from the porch post to a shrub, which is about four feet from the ground. She’s an orb weaver, which means she re-creates her web daily.

“The female’s web is a small orb, 3.0 – 7.5 inches in diameter, typically three to seven feet above the ground in the understory. The viscid spiral may be vertical or sloped skyward up to 45 degrees off vertical. Webs are found in large open spaces in the shaded understory, where they are exposed to a diversity of flying insect prey. Females rest in the open hub during daylight, sensing vibrations from prey striking the web. They hang head down in the center of the web, with the abdomen horizontal and parallel to the ground. The brown and yellow undersurface of the abdomen faces upward and blends with ground litter and vegetation. The light colored upper surface of the abdomen faces downward and camouflages the spider against the light blotches of the canopy. The orb is renewed daily, but the triangular or rectangular silk frame may persist for days or weeks in the same position. At dusk, the female ingests virtually every strand of the web except frame threads, on which she remains until morning. She rebuilds the orb at dawn.” – Anthropod Museum, University of Arkansas

The webs are selective for prey size, retaining mostly flies larger than 3 mm, even though most insects striking the web are smaller. Females are slow moving and almost clumsy, allowing many insects to escape their webs. Of the insects retained by the web, the spiders elect to attack and consume mostly larger flies. About two-thirds of the prey are flies. Beetles, wasps, bees, ants and other similar insects make up most of the remainder of the diet. Unlike other Araneidae, the spined micrathena bites it prey first, then wraps it in silk.

Every morning when I go outside to feed the birds, I see her. The bird food is stored right next to her web. This morning I didn’t see her and fear she may have been plucked out of her web by a hungry bird. Her weaving was a bit messy when I observed it this morning; hopefully she’s hiding – maybe just had a bad night.

I’ll check on her later tonight or tomorrow.

An immature black widow spider has taken up resident on Robert and my cactus in the front yard. I’m thinking it’s a male and hoping there aren’t more nearby. I haven’t had the heart to kill it, since widow spiders are not aggressive (in fact I hate to kill any bug, insect, etc., so I’ll just leave it be).

Click images to enlarge:

(c) BMGN 2009

The immature stages of both sexes and adult male widow spiders may have many red or red-orange or yellow spots and strips on the top of their abdomen. Immature females can be colored gray or pale brown, with numerous banding patterns. Darker coloration increases as they get older. The presence of an hourglass pattern on the underside of the abdomen occurs throughout their development.

(c) BMGN 2009

Male widow spiders are much smaller (about 1/4 size) than the females. They usually are not black in overall color, instead appear light brown or gray and banded. Male widows may have an hourglass pattern, but coloration often is more orange and sometimes yellow. When mature, they have large knob-like structures originating from the head. They are similar in appearance to immature females.

(c) BMGN 2009

Widow spiders build loose and irregular mesh-type webs (which are extremely strong), often on plants, in loose stone or wood piles, or in the corners of rooms, garages or outbuildings. They do not produce the symmetrical web typical of orb weaving spiders or the distinctive funnel pattern web of the funnel weaver spiders.

For more information on the black widow, visit Desert USA. And be kind to spiders.