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Spined micrathena
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Order:	Araneae
Infraorder:	Araneomorphae
Family:	Araneidae
Genus:	Micrathena
Species:	M. gracilis
Binomial name
Micrathena gracilis (Walckenaer, 1805)[1]
Synonyms[1]
Acrosoma gracile (Walckenaer, 1805) Acrosoma matronale C. L. Koch, 1844 Acrosoma reduvianum (Walckenaer, 1841) Acrosoma rugosum (Hentz, 1850) Epeira gracilis Walckenaer, 1805 Epeira rugosa Hentz, 1850 Micrathena gracilis (Walckenaer, 1805) Micrathena matronalis (C. L. Koch, 1844) Micrathena nigrior Chamberlin & Ivie, 1936 Micrathena reduviana (Walckenaer, 1841) Micrathena sexacantha Franganillo, 1930 Plectana gracilis (Walckenaer, 1805) Plectana reduviana Walckenaer, 1841

Micrathena gracilis is a spider in the family Araneidae (orb-weavers),^[1] commonly known as the spined micrathena^[2] or castleback orbweaver.^[3] This spider spins a moderately large (can be about 20 cm long in diameter) and very tightly coiled web. The spiders themselves are small and can be found to be anywhere from 4.2 mm to 10.8 mm long.^[4] Its venom is harmless to humans. M. gracilis is unique in appearance due to its large spiky abdomen and black and white bodies. Certain spiders of this species can also display a yellow color on the sides of their bodies.^[5] These spiders can be seen most active during the end of the summer and beginning of fall. M. gracilis is diurnal and are rarely ever seen active at night.^[6]

Females are 8–10 mm long. They exhibit a bulbous abdomen with spines. Males exhibit a fair amount of sexual dimorphism. They tend to be a fraction of the size of the females. Also, they have fewer spines, a flatter abdomen, and a slightly lighter tone. Although males can produce silk, they mostly use it in the mating ritual.

• 
  The central portion of a web
• 
  View from underneath
• 
  Female lateral view
• 
  Juvenile male anterior

When constructing webs, the inner orbs of their webs are changed every night; however, they may keep the outer layer of the web the same for multiple days.^[6]

Micrathena gracilis is native to North and Central America.^[1] These spiders tend to wander and rarely ever remain in the same web site for more than week. On average, they spend about 6–7 days on each web site. They are neotropical forest spiders and can be found more easily in hardwood forests that contain Oak and Hickory trees. They tend to like moisture; they are more easily found in woodland forests that are near a lagoon, pond, or other small bodies of water. One study mentioned that these spiders were found in an area that tends to flood during their mating season.^[7] M. gracilis may also coexist within and along the edges of colonies of Metepeira incrassata, also known as the colonial orb-weaving spider.^[8] They prey on the skimming bluet and are in turn eaten by white-eyed vireos.^[2]

Micrathena gracilis hatches in the spring, the image of an adult. After the summer's growth, the female lays eggs in a sac. These remain relatively dormant through the winter months. The general life span is one year in length.

Wikimedia Commons has media related to Micrathena gracilis.

• Spined Micrathenas (Fairfax County Public Schools site)
• Spined Micrathena - diagnostic photographs
• Spined Micrathena
• Pictures of M. gracilis
• Illinois State Museum's spider collection