Micrathena gracilis – Spined Micrathena

Micrathena gracilis, commonly known as spined micrathena, is one of the spiny orb weaver spiders. The spiny body serves to protect them from birds, lizards or other predators. The hard spines should hurt predators when dealing a bite. These easy to recognize, unobtrusive forest denizens are abundant throughout the Eastern United States and especially common in late summer.

Description

Spined micrathena spiders have a chunky, pyramid-shaped white or yellow abdomen with black spots and lines along the sides. Another common name of the spined micrathena is the castleback orb weaver – due to its large, bulbous black and white abdomen with spines that reminds of a castle tower. The large abdomen is either white or yellow and has a number of black or dark brown color patterns. On the top, there are often larger black blotches and the tips of the spines are mostly completely black.

The lateral side of the abdomen often has many small dark spots that are aligned in rows. The cephalothorax (head) and legs are usually black or dark brown with some lighter brown or reddish coloration on the dorsal side.

Micrathena gracilis – Spined Micrathena view from side black and white lines stripes — The lateral view of a female Micrathena mitrata. Photo: Katja Schulz

Similar spiders: The white micrathena (Micrathena mitrata) can have a similar appearance and body coloration. Spined micrathenas usually have many spines while the white micrathena only has four on the end of its abdomen.

Size

Micrathena gracilis spiders are small to medium-sized spiders. Their bodies grow to an average size of 0.2-0.3 in (6-8 mm) while some larger individuals can grow to over 0.4 inches (11 mm).

Web

Micrathena spiders spin their orb-shaped webs (up to 1 ft in diameter) horizontally in wooded or bushy areas. They build their webs generally 4-7 feet off the ground.

While many orb weaver spiders rebuild their web every single day, spined micrathenas usually stay around 4-7 days in one web before changing location. They eat the inner part of their web in the evening and rebuild the center part in the next morning.

Micrathena gracilis – Spined Micrathena orb weaver in web — A spined micrathena in the center of its web. As you can see, the center is missing and will be rebuilt the following day. Photo: Katja Schulz

Bite

The venom of the spined micrathena spiders is completely harmless to humans. These spiders hardly bite. Even if provoked, their first instinct is to flee instead of attacking.

Other common names

The Micrathena spiders are also known as Spiny-Bellied Orbweaver and Spiny Orb Weaver.

small spider black and white with large abdomen in virginia is a Micrathena gracilis – Spined Micrathena

Distribution of the spined micrathena in the United States

The spined micrathena is commonly seen throughout the Eastern United States as far west as Texas and North Dakota. More precisely, it is found in the following states: Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia and Wisconsin.