Trachelas Tranquillus – Broad-Faced Sac Spider

The Trachelas Transquillus, or broad-faced sac spider is a spider that is native to the Eastern part of the United States, especially in New England. The spider is an outdoor spider and can usually only be found in homes during the autumn months, when temperatures fall outside.

Trachelas Tranquillus Description

The Broad-Faced Sac Spider has a solid colored, darker brown or reddish cephalothorax that is on the shinier side.

The abdomen, lacking of any patterns as well, is usually more of a tan or gray color with a smooth but dull sheen to it.

One of the most telling signs in identifying the Broad Faced Sac Spider is by the legs.

The legs will be tan, brown, or even with a reddish shade to them and the front pair will always be much darker than the back legs.

Trachelas Tranquillus
The broad-faced sac spider. Photography by: Jenilee Whisler – Central Lake, Michigan

The broad-faced sac spider is sometimes confused with the Woodlouse Spider due to its similar appearance.

Size

The body of the adult female will grow to about 3/8 of an inch (10 mm). If the legs are included, they can reach approximately 5/8 of an inch (16 mm) across.

Trachelas Tranquillus Web

The Trachelas tranquillus does not spin webs to catch prey. They are nocturnal hunters and during the day, they will usually spin a web to create a thin cocoon-like sac to hide in. Therefore, its common name sac spider. These are often found in the crease where a wall meets the ceiling or in windowsills.

Bites of the broad-faced sac spider

The bite of the Broad Faced Sac Spider is initially painful and often produces a painful erythema, similar to that of a bee or wasp sting. This is also due to the large fangs of the Trachelas tranquillus. Some people who are sensitive to arthropod venom may experience more severe reactions. Overall, its bite is not considered medically significant.

Trachelas-tranquillus-broad-faced-sac-spider
A broad-faced sac spider submitted by Anne from Fairfax, Virginia

Scientific Classification of the broad-faced sac spider

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Arachnida
  • Order: Araneae
  • Infraorder: Araneomorphae
  • Family: Trachelidae
  • Genus: Trachelas
  • Species: Trachelas tranquillus

US states where the trachelas tranquillus is found

Trachelas Tranquillus – Broad-Faced Sac Spider range map

As mentioned above, the broad-faced sac spider can be found in the Eastern part of the United States. Mostly in the following states: Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia, Wisconsin

Trachelas Tranquillus – Broad-Faced Sac Spider

26 thoughts on “Trachelas Tranquillus – Broad-Faced Sac Spider

  1. Found this spider on a door frame in my house. I sadly couldn’t recognize what kind it was. This is definitely a first time I’ve seen one like this in Hortonville, WI.

  2. I found this little guy in the bathroom at work in Fort Worth, Texas. He’s kinda far from home according to this. I could be wrong but this definitely looks like the ones shown here. Just a lighter abdomen. If anyone can verify please do. I’d love to know what this is.

    1. Hi there, the spider you found is also in the genus Trachelas but is a different species that is also found in Texas. It’s most likely Trachelas mexicanus.

  3. Found this creeper on my dirty clothes pile in the bedroom. Looks like it started to make some webbing after I got it in the container. Pretty calm when I picked up the pants it was on. To the eye the main body looks black, but when I shine light on it for the camera it seems like a dark red/brown. Tan abdomen and kinda looks to have a stripe of slightly darker tan on the top of the abdomen towards the middle and a dark brown spot on the underside of the abdomen. Located in Michigan.

  4. Hello from Baltimore Maryland 21214. Last night, which is mid Sept., day temps 80s, I was in bed after midnight and felt a sting/bite on the underside of my left upper arm. I reached over with my right and grabbed what felt like a fleshy bug, crushed it with my thumb and forefinger. When I turned on the light, it appeared to be this Trachelas tranquillus. But I experienced no reaction, other than the initial stinging bite. I was quite worried, but I’m ok.

  5. I was watching TV tonight with the lights off and felt something crawling onto my foot and then up my ankle. In the dark, I thought it was a pesky house fly and slapped it. I only stunned it for a second as it fell to the floor. Using my phones flashlight, I realized that was no house fly. I felt immediate soreness at the joint of my ankle/foot. The write up mentioned the potential for infection from feeding on dead insects so I’ll monitor in the coming days. More worried about my 1 year old daughter playing on that same floor. Wish me luck!

    Ps – I live in Connecticut

    1. Hi Jeff, thanks for getting in touch! This is definitely a Trachelas spider. As mentioned on this page, the bite is typically nothing to worry about. The infection risk is something to keep in mind with every open wound, even if not caused by spiders. All the best!

  6. Is this what this is?

    I am freaking out. I just moved out of a bed bug situation. And then was doing laundry, opened a trash bag of clothes in my parents dark gross Boston basement. This is what came out. Two of them. Helppppp I’m going to lose my mind.

  7. Found this in our sunroom on the floor right next to me and my little girl in Covington, IN. I wasn’t sure what kind of spider so I appreciate the information on this website. Thanks

  8. Found this in my kids bedroom. It seems to have came from the window due to the fact that my husband found it under the rocking chair by the window. Can you ID please.? Don’t know if it’s a woodlice spider or trachela tranquilos.

        1. Hi Pete, the shape of the abdomen is not really indicative for the family/species in this case. Gravid sac spiders (both Trachelas and Cheiracanthium) can have a rounded abdomen, less well-fed ones can have a pointed end.
          In this case, the body colors and leg length point towards Trachelas. Yellow sac spiders usually have longer legs and their body colors are yellow or cream colors. Trachelas has that quite unique combination of reddish cephalothorax and legs and a gray/brown abdomen.
          You are right, the linked description above for Trachelas tranquillus does not show Texas on the map. There are a number of very similar looking Trachelas species across the U.S. In Texas, it would probably be Trachelas volutus: https://bugguide.net/node/view/638735
          The species of Trachelas are impossible to ID from a photo alone, so the possible identification on a species level can only be based on the location.

  9. Found this guy in a web hanging on top of my bed when I looked up. I caught him and put him outside. That was before I knew they prefer indoors and it is Texas and it is very hot outside… He did seem to be very active and appeared to freak out as soon as the son hit him when he was in the glass.

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