Tarantula

In terms of their adaptability to the tough Sonoran climate, Tarantulas are a thing of beauty.  But to the uninitiated, they look like a creature from a bad science fiction movie. Tarantulas are the largest spiders in Arizona and more than 30 species make their home here. Adults range in size from 5-10 cm.  Typically, tarantulas are light to dark brown in color and the abdomen and legs are covered with hair.  Mexican-Americans appropriately refer to these critters as aranas peludas – hairy spiders.

Arthropods and arachnids

Tarantulas belong to a phylum of joint-legged animals with external skeletons called arthropods. This is the largest group in the animal kingdom with well over a million and a half described species.  The oldest known arthropods are the extinct trilobites, marine animals that flourished 550 to 450 million years ago.  One type arthropods, arachnids, include spiders, mites, ticks and scorpions.   All of which produce venom. Most arachnids are meat eating and partial digestion begins outside the body when digestive enzymes are poured into prey tissue as the prey is held the animal’s pincers. Prey usually consist of other arthropods. Spiders represent a large group of arachnids.  Approximately 26,000 kinds have been described.

Predators armed with venom and silk

Tarantulas, like all other spiders, are predatory animals and have mouthparts equipped with hollow fangs and venom glands.  When a spider bites, venom from the glands is injected into the body of the prey.  The venom of most spiders is only mildly toxic to man and is not life-threatening. The primary function of the venom is to kill or paralyze prey animals and begin digestion of prey tissues. Spiders have openings known as spinnerets located on their abdomens that are used to spin silk.  The silk producing material is emitted as a liquid but hardens on contact with the air.

Members of the underground

Tarantulas spend most of the lives on or in the ground. They dig burrows when they are spiderlings and live in them for many years, enlarging them as necessary. Once established at at a site, an individual tarantula usually spends its life there, hunting in an area near its burrow.  Tarantulas prefer open areas and avoid conditions of dense vegetation. Tarantula burrows are usually plugged with a loose webbing of silk when the spider returns from a night of foraging. During the winter when the spider is inactive, its burrow is usually plugged with silk, plant debris and soil.

Search for a mate

After the final molt, male tarantulas leave the burrows they have occupied for 8 to 10 years and wander in search of mates. This search usually takes place in the Foothills during the months of June to October.  During this period, male tarantulas may be seen crossing roads and highways and sometimes enter houses, causing consternation (unjustified) among new residents.

Born in a world of silk

After mating, females tunnel under large stones and spin a large sheet on which they lay their eggs. A second sheet of silk covers the first and contains the eggs in a loose bag. Females remain with their eggs 6-7 weeks until they hatch. The young spiderlings remain in the burrow with their mother for days or weeks, eventually dispersing a short distance from their birthplace to take up residence in individual tiny burrows.

Tarantulas make good pets

Tarantulas are preyed upon by birds, lizards, snakes, frogs, toads and javelina.   Tarantulas have several defensive strategies.  The first is to bite.  The second is to rub venom bearing hairs located top rear of its abdomen against the attacker. There are no recorded deaths or severe reactions from tarantula bites in Arizona.  Tarantulas do not bite unless they are severely provoked.  Tarantulas make good pets and they can be handled safely if given reasonable respect.