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.
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.
Size
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.
Web
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.
Bite
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.
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.
References
- Taxon details: World Spider Catalogue
- Binomial name from: Hentz, 1847
- https://bugguide.net/node/view/2000
Milwaukee, WI. Not happy with the results from the from the tool so here you go. My wife found it in the cabinet I sprayed it with glass cleaner and took the pictures.
Hello Julian, I’m sorry that the tool didn’t work for you. Unfortunately, it’s not perfect yet to identify all types of spiders but we are constantly working to improve it.
The spider you found is an ant mimicking spider of the genus Castianeira. Here is a similar-looking specimen on bugguide: https://bugguide.net/node/view/1344064/bgimage
It’s most likely Castianeira longipalpa, given your location.
I was sitting in a park in the Dearborn area of Michigan. I felt something walking between my left ear, so I tried to touch my ear. Then I felt a sting similar to a bee. I was surprised that it was a small spider, brown in the front and black in the back. I photographed it, and after twenty minutes I felt a burning sensation in my body, shortness of breath, and continuous pain in my ear for a period of time. For a whole day I felt pain and burning in my body until the pain subsided. I thought it wa
s a spider of a type similar to an ant spider.
What is this?
Very fast, maybe 1 cm body length. No web. Seen (and photographed) in Boulder, Colorado, today, inside an enclosed patio. It hung around long enough for a couple of portraits, then took off. I went thru your rigamarole, which was very thorough indeed, but can’t figure it out. The closest I can come is the ant-mimic spider, which I am pretty sure it is not. Many thanks! Matt
Hello Matt, thanks for uploading this shot! This is indeed an ant-mimicking spider of the genus Castianeira. Probably Castianeira longipalpa or C. variata: https://usaspiders.com/castianeira-longipalpa-long-palped-ant-mimic-sac-spider/
This small black spider with white stripes on the abdomen fell down into our kitchen sink in Tulsa, OK.
Hello Mark, this is an ant mimicking sac spider, given your location, most likely Castianeira longipalpa: https://usaspiders.com/castianeira-longipalpa-long-palped-ant-mimic-sac-spider/
It’s not a medically significant spider.
This one’s in my kitchen and smaller than a pinky nail. Can you identify?
Hello Eva, this is an ant mimicking spider (Castianeira sp.): https://usaspiders.com/?s=castianeira
To determine the species, I would need to know the location where it was found. There are a number of similar-looking species in that genus.
I looked through all kinds of websites to see if I can find this spider and I could not find not one picture of it. Please help me identify this spider 🙂
Hello Melody, thanks for getting in touch.
This is definitely an ant-mimicking spider (Castianeira sp.): https://usaspiders.com/?s=castianeira
To determine the species, I would need to know the location where it was found. There are a number of similar-looking species in that genus.
Ran across my laptop and table. Less than an inch in size.Maryland
Hello Kam, this is an ant mimicking spider (Castianeira sp.). In Maryland, it could be either Castianeira longipalpa or Castianeira alata. Here is more information about them: https://usaspiders.com/castianeira-longipalpa-long-palped-ant-mimic-sac-spider/
Found in north central Indiana under a porch. Very skittish.
Found in north central Indiana under a porch. Very skittish. Picture 2
Hi Raven, this is an ant mimicking spider of the genus Castianeira. Most likely Castianeira longipalpa: https://usaspiders.com/castianeira-longipalpa-long-palped-ant-mimic-sac-spider/
It looks gravid (pregnant).
Slightly over .5 inches. Front legs mostly a silvery gray, forward facing. Back legs striped with the same gray. Not easily startled, moved pretty quickly. Seen on the ground, not in or near a web.
Candler NC. 7/16/22
Hi Beth, this is an ant mimicking spider of the genus Castianeira, most likely Castianeira longipalpa: https://usaspiders.com/castianeira-longipalpa-long-palped-ant-mimic-sac-spider/
In my last comment I failed to mention where the spider was found. It was found in Midlothian, Virginia. It moved very quickly and it was difficult to capture a good picture as it moved across the pavement.
Hello Eric, this is an ant mimicking spider of the genus Castianeira: https://usaspiders.com/castianeira-longipalpa-long-palped-ant-mimic-sac-spider/
I found it in my house in Eastern Washington state. Very quick mover! Would his bite have left an itchy welt?
Found in Tulsa, OK.
I know this isn’t a spider but can you tell me what kind of bug this is? I found several of this same kind outside in Michigan
I was sitting in a park in the Dearborn area of Michigan. I felt something walking between my left ear, so I tried to touch my ear. Then I felt a sting similar to a bee. I was surprised that it was a small spider, brown in the front and black in the back. I photographed it, and after twenty minutes I felt a burning sensation in my body, shortness of breath, and continuous pain in my ear for a period of time. For a whole day I felt pain and burning in my body until the pain subsided. I thought it wa
s a spider of a type similar to an ant spider.