LEFT: Black widow spider egg sacs contain between 50 and 1,000 spiderlings. Once hatched, they do not hang around very long. They 'balloon' away from the nest in the wind to avoid sibling cannibalism. RIGHT: The black widow female remains on guard at all times when egg sacs are present. Should an intruder approach the web, the spider will hide but not leave the sacs. Staff photos by Jennifer Greenwell
What appeared to be a random, chaotic mess of silky string strewn over a large, low area of a rock wall blocked this reporter’s way to a water spigot one summer day. On closer inspection, the three-dimensional mass extending out over a patch of grass was a killing field of insect legs, heads, and wings surrounded by hundreds of tiny, pollen-like specs. Overseeing this grisly collection, was a glossy, black spider with a piercing, blood-red hourglass on its underbelly. Turns out, the “pollen” was hundreds of black widow offspring.
Central Texas is home to three species of Latrodectus, or true widow, spiders: southern, western, and northern. They are differentiated by markings and size. In other countries, they are called button, shoe-button, and hourglass spiders.
Widow spiders are sexually dimorphic, meaning the females and males look different. The female is about 1.5 inches long and has a large, globe-like, glossy black to dark brown abdomen with a red or red-orange marking that is often hourglass-shaped, but sometimes just spots. The male is about half the size and has a much smaller abdomen and slightly longer legs. It is often brown with white/orange/red stripes or dots, but no hourglass mark. Baby widows start out with an orange-to-brown appearance.
The male widow searches out females through pheromones, chemicals that contain clues as to whether she is ready to mate and even if she has recently eaten. Once he has found a female, the male rearranges her web to minimize escape routes and increase the chances of mating. As he approaches, he makes his presence known by tapping the web and her — he does not want to be mistaken for a dinner guest. He will wrap her in silk webbing called a bridal veil to buy him time to escape should she respond aggressively.
After they become better acquainted, the male rarely sticks around, although the sperm he leaves behind can last up to five months. Once eggs are fertilized, the egg sac is laid on the web and heavily wrapped in silk, forming a round ball about a half-inch in diameter.
Black widows are most likely to bite intruders while guarding their egg sacs. If a black widow feels the sac is in harm’s way, she will relocate and make a new web. Females can lay three to five sacs containing 50 to 1,000 eggs each summer. Spiderlings erupt in three to six weeks, but only about a third survive to adulthood.
A black widow typically dines on insects, particularly any that get stuck in her web. Upon feeling vibrations, she scurries out to greet the guest, quickly injects her prey with venom to subdue it, wraps it up in silk, and drags it back to her retreat in the web.
Fifteen times more potent than rattlesnake venom, black widow venom is a fast-acting paralytic that affects the nervous system. In people and pets, it can cause muscle cramps, nausea, vomiting, sweating, difficulty breathing, chest tightness, heart irregularities, and sometimes speech difficulty, but rarely death. Male and juvenile black widows are not dangerous to humans.
The sight of a black widow can be alarming, which is the arachnid’s first line of defense. The aposematic marking is nature’s warning sign to stay away. Females and juveniles can shoot out a bit of sticky silk, called silk flicking, to discourage predators.
The widow’s most-often-used defense mechanisms are fleeing and hiding. It also plays dead. Biting is a last resort. Predators include other spiders, birds, praying mantis, wasps, mammals, lizards, and, of course, humans, which don’t actually have much to fear from what many think of as terrifying and dangerous creature. Even so, the best advice if you stumble across a black widow is to keep your distance, which this reporter did, but with a camera in hand.
DID YOU KNOW?
Black widow spider silk is several times stronger than any other spider silk.
During World War II, black widow silk was used to make crosshairs in gunsights for the U.S. Army.
Researchers are studying the chemical makeup of widow silk, hoping to produce super-synthetic fibers.
By weight, black widow silk is stronger than steel.
Black widow venom is 15 times stronger than rattlesnake venom.
Brown widow venom is three times more toxic than black widow venom, but they make less of it.
Despite having eight eyes, the black widow has very poor vision, relying on vibrations on her web for information.