The huge pointy spines on the abdomen of the Arrow-shaped Micrathena Spider are just the first of many wonders that make this spider so attractive.
Arrow-shaped Micrathena Spiders are everything their name suggests. Instead of a round abdomen, seen in typical spiders, abdomen is longer and generally triangular in shape, like the head of an arrow. Like other Micrathenas, this species' female has sharp spines on it that resemble rose prickles. They protrude from the edges of the abdomen. These spines are believed to ward off predators, but some sources suggest they may add to her ability to conceal herself in her web. Two large points extend from the bottom of the abdomen and angle away from each other. They are thick and intimidating with red bases and black tips. Males do not have spines of any kind; their abdomens have rounded edges.
Male are mostly black with white edges, but females abound in color and pattern. The head, legs and most of the body are red. The center of the arrow-shaped abdomen is bright yellow with small red spots. Most of the medium and large spines are tipped with black. Females are twice as large as males. Both genders spin orb-shaped spiral webs that lie in a vertical plane (up-and-down). These webs may only be a few feet off the ground. A thick, short, zigzagged strand of webbing, called a stabilimentum, is usually just above the center of the web. Many spiral strands radiating from the center allow the spider to tread easily on its web. Orbweavers are known to rebuild their webs every day.
In autumn, a female Arrow-shaped Micrathena Spider will lay fertilized eggs on the edge of her web, usually on a leaf right next to it, and then die before they hatch. The eggs will overwinter in the egg sac and hatch the next spring. They prefer outdoor habitats with vegetation to help hide them. Look for them in forests.
Scientific Name: Micrathena sagitatta
Other Name(s): Arrow Spider
Size (Adult; Length): 4mm to 9mm (0.16in to 0.35in)
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Legs: Spiders have four pairs of legs and these are attached to the cephalothorax.
Pedipalps: Small appendages near the mouth used as taste and smell organs.
Cephalothorax: Contains eyes, head, mouthparts, and legs.
Abdomen: Contains various organs related to digestion, reproduction, and web-making.
Spinnerets: Used in the production of spider silk for fashioning webs or catching prey.
NOTE: Unlike insects, spiders have both an endoskeleton (internal) and exoskeleton (external).