Castianeira Longipalpa – Long-Palped Ant Mimic Sac Spider

Castianeira longipalpa, sometimeys referred to as the long-palped ant mimic sac spider is found along the Eastern United States as well as in the Pacific Northwest. The small black spider with at least four white lines along its abdomen is not medically significant. Castianeira longipalpa is often confused with its close relative,

Long-Palped Ant Mimic Spider Description

Despite its name, the long-palped ant mimic sac spider does not look much like an ant. However, all spiders of the ant-mimicking spider genus Castianeira behave and move similar to ants. Like its close relative, the red-spotted ant mimic spider (C. descripta), it is often observed holding its two front legs up in order to appear like a six-legged ant with antennae. The reason for this behavior is not entirely clear yet. It is believed that this behavior should help them get close to ants in order to prey on them.

C. longipalpa can have some different appearances, depending on age and sex. The abdomen of the spider is always black with at least four lateral white or light gray stripes. The cephalothorax (head area) can be black, brown or grayish, almost white. The legs are completely translucent brown in juveniles. In adults, the two front leg pairs are usually brown towards the end and black at the beginning close to the body.

Castianeira longipalpa or Castianeira variata found on Staten Island New York black spider with grey white stripes
Castianeira longipalpa. Photo by: Shannon Staten Island, NY

The two hind leg pairs of adult specimens can be black with white bands, completely black or also bicolored in black and brown.

Note: Castianeira variata which occurs in a similar range in the Eastern United States. Exact identification can be impossible without examining the spider under a microscope. Therefore, there is no guarantee that all images on this overview actually reflect C. longipalpa. C. variata is also not medically significant, so an exact species level ID might not be necessary for the purpose of reader safety.


Despite the much larger appearance on the images here, C. longipalpa are relatively small spiders. An adult female can reach a body size of maximum 1/2 in (13 mm). Males and juveniles are often much smaller with body sizes between 3 mm to 6 mm.

Castianeira longipalpa found in Northwest Georgia ant mimick spider black with white stripes brown legs
This C. longipalpa found by Brian in Northwest Georgia is about the size of half a dime (0.3 in or 8 mm). Including its legs, it reaches about 0.7 in.


As other spiders of the Corinnidae family, the long-palped ant mimic spider is a hunter spider. It does not build a web to catch its prey but actively hunt ants and other small critters. They only use their silk producing abilities to wrap their eggs in protective egg sacs and to build a nest to place the egg sacs in.


C. longipalpa is a fast spider and may seem somewhat aggressive due to its speed. However, their first instinct when approached by much larger humans or pets, their first instinct is generally to flee. Therefore, bites are relatively uncommon. Due to their size, they may even have difficulty even piercing through human skin. In the rare cases where an actual bite might occur, the symptoms are usually limited to minor localized discomfort such as swelling or some pain comparable to a bee sting.

Ant mimick spider Castianeira longipalpa Eastern USA black spider white stripes brown legs
Photo: Mr Bo Northern Chester County, Elverson, Pennsylvania.

Scientific Classification of Castianeira longipalpa

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Arachnida
  • Order: Araneae
  • Infraorder: Araneomorphae
  • Family: Corinnidae
  • Genus: Castianeira
  • Species: Castianeira longipalpa

Distribution of the Long-Palped Ant Mimic Spider in the USA

The long-palped ant mimic spider is found throughout the Eastern United States, east of the Rocky Mountains. Independent populations also exist in the Pacific Northwest in Oregon and Washington. Hence, it is found in the following U.S. 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, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, Washington, West Virginia and Wisconsin.


Castianeira Longipalpa – Long-Palped Ant Mimic Sac Spider

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