Introduction

Spiders have a characteristic appearance, which is easily recognized by most people. They possess eight legs, which immediately separate them from insects, which only have six legs. Spiders lack wings and antennae. Their bodies have two regions; a cephalothorax (fused head and thorax) and an abdomen. Young spiders (spiderlings) resemble their adults except for size and sometimes color. All spiders have a pair of jaw-like structures called chelicerae, at the end of each is a hollow, claw-like fang, which has a small opening through which the venom is injected. Spiders are considered beneficial because they feed on insects, but are considered a nuisance because of the webs they spin. The only two species considered dangerous in the United States are the Black Widow and the Brown Recluse spiders.

 

Black Widow Spider

image of black widow spider Female black widow spiders are easily identified because of their globular, shiny black abdomen with a reddish or yellowish characteristic hourglass marking. The abdomen is about ¼ inch in diameter but may be as large as ½ inch when the female is full of eggs. Males are much smaller and lighter colored, with light streaks on their abdomen. The black widows web is an irregular mass of fibers with a small central area to which the spider retreats while waiting until its prey becomes ensnared. These webs are frequently constructed underneath boards, stones, or the seats of outdoor blackwidow spider privies, along foundation slabs, behind shrubs and especially where brick or wood sidings extend close to the ground level. They rarely enter a residence. Their venom contains toxins that affect the nervous system. The severity of a person's reaction to the bite depends on the area of the body bitten, the size of the person, the amount of venom injected, depth of bite, and the person's sensitivity. The bite produces a sharp pain, which disappears rapidly. Muscular cramps are felt 15 minutes to several hours after the bite, spreading and becoming more severe as time passes. The venom then grows weak, tremors develop, and the abdominal muscles show a board-like rigidity. Respiration becomes spasmodic and the patient is restless and anxious. During this period, a feeble pulse, cold skin, labored breathing and speech, light stupor and delirium may be noted. Convulsions and death may result with some victims, especially if the person is sensitive and no treatment is received. Black widow specific anti-venom is available to most physicians.

 

Tarantula

tarantula spiderTarantulas are our heaviest spiders by weight and have a body length of about 1 ½ inches (40 mm). They are relatively common throughout Texas and their large size makes them quite recognizable. Typically, the head-thorax region (cephalothorax) and legs are dark brown, the abdomen brownish black. Color may vary between individuals and certainly changes after a molt.

Females lay 100 to 1,000 eggs in a web which is constructed like a hammock. The egg sac is retained in the burrow, guarded, and usually held by the female. Eggs hatch in 45 to 60 days. Spiderlings hatch in July or later in the year within the egg sac. Once they leave the egg sac, the spiderlings may stay with the females for 3 to 6 days or longer before dispersing. Many of the young fall prey to other spiders or predators as they disperse to begin their own burrows.

Like other spiders, tarantulas have "fangs" on the end of the chelicerae which inject poison when they bite prey. Spiders only ingest liquid food but they will chew the food somewhat while they feed. Tarantulas occur throughout Texas and are common in grasslands and semi-open areas. Tarantulas use burrows, natural cavities under logs or stones, spaces under loose bark of tree trunks and even old rodent burrows as shelters. They also dig their own burrows. Webbing is sometimes used to line the shelter and a few lines of silk are placed on the ground in front of the shelter to detect passing prey. These spiders usually are restricted to the ground but can climb. They usually remain in the burrow waiting for prey to come by but may move a few meters out to forage when necessary. They typically feed on crickets, June beetles, ground beetles, grasshoppers, cicadas, and caterpillars. One of the most spectacular spider events in Texas occurs for a few weeks each summer when male tarantulas actively wander apparently seeking females.

 

Brown Recluse

A recluse spider, Loxosceles sp., female. The shape of the cephalothorax (head-thorax) region and darkened violin markings on the carapace (top of the cephalothorax) are useful identification marks for most of our recluse spiders. Recluse spiders have six eyes in three pairs or diads and a carapace that is quite flat when viewed from the side and highest near the head. The fangs or chelicerae are fused at the base.

The color is generally yellowish brown but it can vary. The most distinctive mark is the darker violin shape on top of the carapace. The base of the violin mark is at the front of the carapace and the "neck" of the violin extends backward toward the abdomen. Body length of the female is 3/8 inch; length of the male 5/16 inches.

Mating season is from April to July. Females produce up to 5 egg sacs containing about 50 eggs in each. Development to adult may take nearly one year. Laboratory records indicate that they may live for several years as adults. The spiders form a loose irregular sheet web which is used to capture prey and as a retreat. They also form loosely constructed egg sacs that are attached to a surface.

image of a brown recluse The brown recluse occurs from Ohio south to Georgia and west to Nebraska and Texas (although there are no records yet from the Lower Rio Grande Valley). They usually are found under logs, stones, or other sheltered areas, preferring undisturbed habitats. They can be found indoors where they hide in dark corners, in trunks, under stored clothing, and around almost any undisturbed structure.

The venom is potentially harmful to humans. Recluse bites usually form a red circular area on the skin which sloughs off the skin leaving an open wound which is difficult to heal and may require several months before it is completely healed. Reactions vary in severity, depending on the sensitivity of the individual. Seek medical attention if such a bite occurs. This spider is quite non-aggressive and bites occur most frequently when it is injured or killed. This may happen when trapped in clothing or bedding. Bites often occur on the buttocks or legs. They typically produce local pain and itching which may take days or over a week to occur. Systemic (generalized internal) reactions usually are evident within 72 hours. The bite site may develop a discolored pustulate area that progresses to a necrotic area with an open wound the size of a quarter or larger. Systemic reactions may include rashes, fever, generalized itching, vomiting, diarrhea, shock or death.

 

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