Black Widow Spider

SCIENTIFIC NAME: Various
CLASS/ORDER/FAMILY: Arachnida/Araneae/Various
METAMORPHOSIS: Simple

Introduction:

Non-insect arthropods with 2 body regions, cephalothorax (head and thorax) and abdomen connected by a tiny waist (pedicel). Antennae absent. Usually 8 simple eyes, occasionally 6. Below eyes are 2 chelicerae or jaws which end in a hollow fang, connected internally to poison glands. With 1 pedipalp (palp) between chelicerae and 1st pair of legs on each side. Legs slender, 4 pairs. Abdomen unsegmented, with a group of fingerlike spinnerets (produce silk) on posterior or rear end. Males usually smaller than females and with terminal pedipalp segment greatly swollen, may also differ in coloration. The immature stages are egg and spiderlings, the latter closely resemble the adults except for size and sometimes coloration.

Identification

Since black widow, brown recluse, and Hobo spiders are of primary importance in human environments, their identification is essential. Several different species may be involved and which can only be identified by experts. However, group recognition alone is sufficient for the purposes here.

Black Widow. Adult female body length about ½" including an almost spherical abdomen about ¼-3/8" in diameter, with overall length including legs of about 1 ½ - 1 3/3"; males about half female size. Color typically black, abdomen on underside with 2 reddish triangular markings usually joined to form a reddish hourglass-shaped marking but sometimes separated (“split hourglass”) or only a single mark; usually with red markings above spinnerets.

Characteristics:
An important characteristic of the black widow spider is its comb foot. This row of strong, curved bristles is located upon the hind pair of legs and is used to pitch silk over captured prey.Black widows are shy in nature. They are solitary, socializing only during copulation. Black widows are nocturnal and spin webs during daytime. They can sometimes be seen hanging upside down in their web, exposing a telltale hourglass abdominal marking. This marking is bright red and signals danger to predators and attackers.

Male vs. Female
On average, male black widow spiders are smaller than “>females, reaching only about half their size in length. However, the legs of the male black widow are considerably longer in proportion to the female’s and are marked by orange and brown at the joints. Males may exhibit red and white stripes on the abdomen depending on the species and are more colorful and finely patterned than females.

Biology

After mating, females produce egg sacs. Depending on the species, one or more sacs may be made. Early instars (spiderlings) spin a silk thread into the air and float out on the breeze like kites. This is called ballooning and provides for general dispersal of the species. Spiderlings go through 4 - 12 molts before maturity. Most spiders live for 1 to 2 years. Spiders are predators, paralyzing or killing their pry with venom. They typically feed by injecting a predigestive fluid into the body of their pry and then suck in the digested liquid food. Spiders can survive without food for several weeks to a few months. Most spiders are nocturnal and hunt or capture prey primarily at night. During the day, they hide and remain inactive in cracks and crevices. Spiders rarely bite people and only do so as a means of defense.

Eggs

Egg sacs are white, tan or gray in color, have a paper-like texture, and measure 12 to 15 mm in diameter. They may be pear-shaped or globular. Each egg sac contains hundreds of eggs, from which hundreds of spiderlings emerge. However, only a handful of these young survive, as black widows are cannibalistic during the
early stages of their lives.

Control

Spider control is a multi-step process:
Inspection. A thorough inspection of the building is essential and many have to be made at night because most spiders are nocturnal. Identification. Accurate identification is important for both pest management and
medical reasons.

Prevention. This consists of making sure that the building is in good physical condition, and properly screened and sealed to reduce entry. Also, changing the lighting to off-building locations, from mercury vapor to sodium vapor lamps, or in the case of homes, changing the bulbs near the entrances to yellow bulbs, may be of help in reducing attractiveness to insects and hence spiders.

Sanitation. Such practices consist of keeping the premises free of debris such as boxes, papers, clothing, lumber piles, etc; it is wise to wear protective gloves and clothing when cleaning out such accumulations of clutter. A thorough housekeeping should be done twice each year. Outside, remove debris, firewood and lumber piles, landscape timbers, stones, etc. Keep the grass mowed to 3” or less and trim back any vegetation in contact
with the structure.

Mechanical measures. The key to control is the timely mechanical removal of spiders and webs, but especially the egg sacs with a vacuum, both inside and outside; seal and dispose of the bad immediately. If a broom is used for the removal, then it is suggested that if a spider is present on the web that an appropriately labeled insecticide be used for a quick contact kill before removal of the web.

Pesticide application. If desired, chemical control consists of the application of appropriately labeled dusts, wettable powders, microencapsulated, or lacquer pesticides in typical spider harborages. Perimeter treatments are helpful. If web-building spiders are the problem, lightly dusting the web with a non-repellent dust is very effective. Control of spider insect food is desirable but will only help in long term as spiders can go for weeks or months without food.