Sunday, March 3, 2013

Spider Sunday: Flatties

Many spiders go unseen by the casual observer because they emerge only at night. Venture outside after dark, and you are likely to be astounded by arachnids you never knew existed. Take a flashlight to the outside walls of your own home and there will likely be spiders prowling across it. If you live in Florida or the southwest U.S., you will eventually see crab-like spiders of the family Selenopidae, called “flatties.”

I might not have recognized them myself were it not for Zack Lemann, Chief Entomologist at the Audubon Insectarium in New Orleans. We occasionally meet up in southern Arizona for the Invertebrates in Conservation and Education Conference at the end of July each year. In 2010, on a night field trip to Madera Canyon, Zack identified a spider sitting motionless on the outside of a restroom building as a “flattie.” I had figured it was a running crab spider in the family Philodromidae and appreciated the correction.

Flatties can be easily confused with any number of other spiders, but are readily identified by a few distinctive characteristics:

  • Extremely flattened appearance. They look like they have already been the victim of someone’s shoe, so flat are they. Even the legs look cock-eyed, oriented almost completely horizontal to the body. This distinctive leg configuration is called “laterigrade,” and only a few other spider families have this feature.
  • Legs increasingly longer from front to back. Note that in philodromid crab spiders like the one shown below the second pair of legs is the longest.
  • Six eyes in one row. Six of the spider’s eight eyes are in one row across its face. The other two set back on either side of the face.
  • Rear edge of sternum is notched. You have to turn the spider belly-up to see this character (good luck), but this feature of the “chest plate” is diagnostic.


Philodromid crab spider (note long 2nd pair of legs)

Their thin bodies allow flatties to slip into very narrow cracks and crevices, where they hide during the day. Most references indicate that these spiders hide under stones, or beneath bark on logs or trees, and between the bases of leaves of dense plants. I have personally never discovered them on the ground or under objects. They have always appeared on vertical surfaces at night in my experience.

These are medium-sized spiders, adults measuring from 7.5-13 millimeters in body length. Their sprawling legspan makes them appear larger. The mottled gray or brown or yellowish coloring helps to camouflage them on rock surfaces and tree trunks. They likely wait in ambush for prey, though when disturbed they can sprint with startling speed.

There are five species found north of Mexico, all in the genus Selenops. They collectively range from southern California to western Texas, and also in Florida and the Caribbean islands.

Sources: Jackman, John A. 1997. A Field Guide to Spiders & Scorpions of Texas. Houston: Gulf Publishing Company. 201 pp.
Kaston, B.J. 1978. How to Know the Spiders (3rd Ed.). Dubuque, IA: Wm. C. Brown Company Publishers. 272 pp.
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds). 2005. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

53 comments:

  1. I see them often - but never got one ided beyond the genus. One should think that with only 5 spp....but no ):

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    1. I suspect one has to look at a specimen's reproductive organs to get to a species ID, and that can't be done from images alone of the top of the specimen.

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    2. https://m.facebook.com/story.php?story_fbid=1940465432639465&id=100000280805879

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    3. This is a flattie that landed on my head in the dark. Never seen a spider so flat before. I first thought it was a recluse. I trapped it in a crystal glass. A picture of its under belly for you. I live in the Florida Keys

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    4. Kathleen: All spiders are capable of biting, but flatties are *not* considered dangerously venomous (unless your immune system is compromised or hypersensitive). I would not worry. :-)

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    5. Recluses are also not known to be in the Florida Keys.

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    6. Saw one on my backyard fence this morning in central California

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  2. I found one of these on my lake and I live in MA is it poisonous I have two kids

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    1. Dee, "flatties" do not occur in your area. What you are seeing are "running crab spiders" in the genus Philodromus, family Philodromidae. They are *not* dangerously venomous (bite), nor are they poisonous (toxic if eaten).

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  3. I know you say it only lives in the southwest, but we found one and it doesn't look anything like the above link you posted. It looks exactly like the pictures in your blog. The way our food is shipped around North America can't they find their way to other areas?

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    1. Steph: Again I would suggest it might be a philodromid crab spider (family Philodromidae), or possibly a giant crab spider (family Sparassidae), rather than a "flattie." Yes, giant crab spiders sometimes hitchhike on bananas and other foods and products from the tropics. Without seeing a specimen, or at least a clear image, I cannot speculate further.

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    2. I live in North Florida and find them all the time I have photos also of both the top and abdominal reigon of the spider

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  4. i think i found one well, actually 2 now.... in my room.... 1st one i panicked and sprayed the life out of it. sorry.... (i prefer relocating,) then the 2nd one tonight. this one is much smaller but for sure the same type.this one got the broom but i didnt see it till it was already dead and not whole. i have pics of both, can i send them to you? i only paid attention to the eyes tonight.... really wishing for confirmation that these arent poisonous as i sleep on my floor and as interesting as they are, they make my skin crawl thinking of possibly more in here.
    thanks
    ps... am sleeping in the livingroom tonight!

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    1. It would help to know your geographic location. Their could potentially be other spiders of concern that resemble flatties, if you are outside of North America....I'll rarely reprimand someone for killing the odd spider in their home, especially if it is unfamiliar. The overwhelming majority of spiders are in no way endangered species.

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    2. i am in san diego, southern california.
      i have some good pics, spray leaves them in much better condition than squishing! any way to send one to you?

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    3. Post the images online and then send me a link to them, please.

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  5. Hey! Im Im Kenya, maasai land (1h30 from Nairobi ) for a month and I already saw 2 of them corresponding perfectly to the pictures you posted in you're blog. Their behaviour fits totally with what you said about them. I just wanna know if I should rather kill them or if there is no way the would bite me cause I'd don't mind letting them walking around if no danger ? (and by the way are they poisonous ?)
    Thx !!

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    1. Being unfamiliar with African spiders, I would hesitate to say that what you are describing *are* flatties. I would try and find a local expert to make the ID and decide whether they are dangerously venomous (nearly all spiders are venomous, but few pose any threat to people).

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  6. Oh okay, thank y ou in advance!

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    1. No, I mean *you* need to contact a local expert. I live on another continent!

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    2. hi eric, so, yesterday bumped the # of these beautiful and terrifying spiders found in my room to 4, and possibly a baby but that could be my overactive immagination.... i think i am going to spray the heck out of my room, maybe even set off a spider bomb. as much as i dont want to, i just dont know what else to do.still have not found a picture that comes as close to my guests as the flatties you picture here. will a bomb or spray keep them away or do they only kill on contact? im sorry, you arent a bug spray person.... im just so freeked out that i dont know what to do and the safest place i can think of is near someone who is familiar with the beasts i am battling... hence the frequent messages....
      so, as a way to take the fear out of them, i am trying to learn as much as i can about them but its hard when i still am not knowing what they actually are. thanks for any help or direction you might be able to offer.

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    3. I understand; but, they are not dangerously venomous, and are probably killing insects in your home that *could* be pests. You might weigh that possibility along with your fears? You have my empathy, I assure you.

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    4. I have a picture we think isn one of these in Oklahoma

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  7. Thank you for the article! These are very interesting spiders, and very cool. It's always difficult to correctly identify the many species of insects and arachnids despite studying the bulk of them! I recently read an article that a species of "flatties" in the rainforest are able to glide to the forest floor using their flat bodies and front legs to guide them in case they fall. Completely incredible.

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  8. Are they dangerous I just found one tonight and I stay miami

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    1. No, not dangerous to the average, healthy human being.

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  9. Hi eric,
    After much research I seem to have fallen in love with these 8 legged creatures and not seen a single one since my last comment here. Am moving to South India in a few weeks and plan on doing more research on all the new crawly things I find there.
    Sincere Gratitude for changing the way I think about things that have a lot more legs and a different lifestyle than my own.

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  10. No, you may not replicate any part of my blog, sorry. You can hire me to write for you if you like, though.

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  11. Hi Eric, I think we might have something like this at home. I am very scared of spider any size and type due to the fact that most of our spiders and insects are poisonis. Im from South Africa. I asked my hubby to take a photo of it. Its looks similar to something we call a "reën spinnekop" roughly translated to rain spider. Although I noticed rest of the worlds " rain spiders dont look the same as we South Africans translated it to be. These ones are flat with leg span much greater than their body size, the 2nd pair of legs are much longer in length. When they run they lift their body from the surface actually hard to explain. They tend to invade your home more during rain times - hence their "name". Normally they have roundish body although the one i took a photo of has a more sharpish end to his back body.

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    1. I'll have to look up the name that you give and see what family that spider belongs to. I suspect, from your description, it is either in the Philodromidae or Sparassidae.

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    2. Ues, Im from South Africa too. These rain spiders are huge.. HUGE. And sre they and flatties poisonous for my African grey? They are bloody everywhere and impossible to kill eoth poison. I'm one. And they are thousands. I live against a mountain. It's no pleadant entertainment. We have a genetic resentment of these many legged creatures. Shame. I always feel guilty as well as they do getcrid 9f other annoying insects.

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  12. I live on SE coast of FL, have seen 3 of these in my home. The first was on back porch, a fairly big one, body ~8-10mm, slid out from a ridiculously tiny crack ... an internet search for "very flat spider" immediately identified it. Happy to see it--spiders good, I no like bug poison. Nice to learn these sound harmless and elusive. Saw second one in garage awhile back, about same size, but last night I found a little one, body ~4mm, in a stack of mail that had sat on the counter overnight. We startled each other. I carried her (judging from shape of pedipalps) to the back porch. Searched internet again today just to reassure myself they're harmless. But now wondering if it hiding in such a public spot was just a fluke, or if these guys are likely to start popping out from under or between anything I leave sitting around.

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    1. Clutter is a great way to become familiar with all sorts of strange creatures! :-) I speak from experience.

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  13. Hello, I need someones insight on this. I had my car door open and saw a spider basically glide onto the side of my dash and ran off somewhere in my car. I saw an article on it from the Washington post. They named these spiders "Flatties" My main concern is, is this poisonous? Or will it have a nasty bite? I live in Florida as well. Thank you in advance to answering this

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    1. There are several spiders in Florida that match your description in terms of behavior. While nearly *all* spiders are venomous, very few are dangerous to healthy people or pets. Flatties are not among them, nor are the huntsman spiders you have down there. Only widow spiders (Latrodectus spp.) and brown spiders (Loxosceles spp.) warrant concern in your state, and even brown spiders are rather uncommon in peninsular Florida, from my understanding.

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  14. Hi Eric.

    I live in Namibia. We have a lot of odd spiders here, especially in the Bush. However, we also have a lot of common house spiders. Aside from the common Daddy-Long legs, we have a breed of Selenops as well. In most cases, they get sprayed, whacked or squashed.

    Going through your description, it definitely is a Selenops breed. Now, I am a major arachnaphobe. I have a small Selenops in my room (no more than the size of a thumb without the legs). Having done my research I found it is a female. At first it kept a wide birth from me, hiding as soon as I enter the room at the fat end. Soon, it was gone for a while and then returned, closer to my bed. :(
    Now, I did want to kill it but took a different approach. I called it Dougie. It literally barely moves. At the moment it's at arms length from me. Now, it's not skittish anymore when I enter or climb into the bed. It has a fondness for the location where I am conducting an experiment on a natural repellent of insects for orchids using mold. I get these tiny little fruit bugs that annoy the crap out of me.

    (Sorry for the long story...)
    My questions... Is it normal for a spider to become more... "friendly" towards a person? Meaning, is it normal for me to be a breath away and he thing doesn't bolt.
    Secondly, they aren't poisonous or weird in any way... right? Because Dougie has been coming closer to the proximity of my pillow when I sleep, scaring the bejeezus out of me when I wake up.
    Thirdly, what do they eat and do they even drink water? She seems really content on that area with the tiny flying fruit bugs.
    (Named her Dougie before I knew it was female... name stuck.)

    The largest selenops I've seen was about flat the size of a palm... with legs extended. I think that one had a happy life.

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    1. Yes, I think many small organisms can become habituated to the coming and going of a larger animal when it becomes apparent it is not a threat. Nearly all spiders are venomous, but no selenopid is dangerously venomous to healthy human beings, as far as I know. Thank you for sharing your story!

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  15. I found one of these on my driveway yesterday after my daughter drove off. I was sure it had been squished, but it was different from our normal spiders (I'm in SW Florida, I have wolf spiders and MANY crab and other non dangerous spiders, but also brown widows, which are dangerous but not aggressive.) Anyway, I gently touched it with a stick and was shocked when it moved! I'd never seen such a flat LIVING spider. It was slightly smaller than a half dollar, legs and all. Just to be sure it wasn't dangerous, I checked online and it looks exactly like your photo here. That never happens. Lol! I'm good with spiders as long as they aren't aggressive and dangerous, so I'm pretty psyched to have seen a new one. Thank you for your page and article! Now all my family and friends know about this new one. (Btw, the post from Anonymous in Namibia was really fun!)

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    1. Thank you for sharing your story and for the kind compliments. :-)

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  16. I think this is the spider they has been hanging out on my truck and comes inside when I open the doors (for a couple weeks now). I finally found a place it hid (under my 10 month olds car seat) I put it in my trunk and saw it underneath, I quickly put the car seat on the ground & it fell off & then started hopping/jumping on the ground under my truck. It’s always been during the day, does it sound like it could be this spider??? How can I send a pic??

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  17. Are they dangerous to a toddler?

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    1. No, they are not dangerous to the average, healthy human. Did you not read all the other comments?

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  18. Hello Eric,

    Thank you for all of you insightful writings

    I live in south florida and have a bedroom on the 2nd floor that has several flatties appear on the ceiling of room & closet. There is an attic above.

    Beside trying to pest control for local roaches etc and seal and gaps

    Is the a particular spray, fumgiation, etc that i can use in attic to get rid of them. It is very unnerving I appreciate any recommendations

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    1. I'm sorry, but I do NOT give pest control advice, for a variety of reasons that I outlined in one of my posts:

      http://bugeric.blogspot.com/2017/08/why-i-dont-give-pest-control-advice.html

      I have never heard of anyone being bitten by one of those spiders, though.

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  19. Hi Eric! I stumbled on your blog today bc I recently relocated to southern/central Florida. Because I grew up outside of Chicago many species here are unfamiliar to me—like the small, flat spider I’ve seen on the ceiling and in my mailbox. Although I’m still not sure if it is a flattie or just another crab slider, I’m confident it is t a brown recluse and that is sufficient for me!

    I’m looking forward to reading more of your posts! I grew up catching and holding the “cute” bugs (like ladybugs, lightening bugs, butterflies, mantids, grasshoppers, etc.) and turning over rocks to look for grubs, but I’d run from honeybees, freeze when I’d see wolf spiders, and spitefully destroy red ant hills.
    I recently started keeping honeybees, but before I got a colony I learned as much as I could about them in order to care for them better. That stemmed into learning about OTHER bees, then wasps, then hornets, and then trying to identify and learn a little about these new bugs I’ve never seen before. Learning about bugs that I was fearful of before has definitely made them less scary...in theory. I still freeze when I’m surprised by a spider, haha!

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  20. Stay in Namibia, Africa. Flatties are all over. I have a phobia for spiders, any spider. Came here to read a bit about them, in hopes it will help me understand the little monsters a bit better. One step at a time. I am glad to see they are not poisonous though.

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  21. These are close to my tomatoes plants and jalapeños and habanero plants

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  22. Recently my wife was bitten by a baby spider that looks similar to the photos you posted. The next day she had lost all use of her right arm and was in unbearable pain. Then she developed lesions on her face that were like open sores. She called the hospital and they suggested she take antibiotics immediately and get a tetanus shot just in case. This is a reaction from a baby spider so could you imagine if she had been bitten by the mother spider! It looked identical to the photo but the body had a Violin shaped body and a pale tan color. The babies were super aggressive. Any idea what this spider could have been? This happened in West Palm Beach, FLORIDA.

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    1. Hmmm I wonder what spider that was since it had such different characteristics from a flattie. Did I miss the response? I live close to you so this really would be good to know. I hope your wife is completely recovered!

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    2. I have been unable to reply given problems in agreement between my web browser and Blogger. I am sorry....I do not have an answer for you, though. Without seeing the specimen, I cannot identify it for you. I hope your wife is completely recovered.

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  23. Hello ~ I live in Manatee County, FL, and often encounter ‘flatties’ during the Spring months. I typically notice them in my mailbox … usually just one. I have noticed they like to hide in between pieces of mail. They are very hard to sweep out due to their speed. I have not noticed them to be aggressive, but they do startle me when gathering my mail!

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  24. Hello, i found one in my home in the Dominican Republic, i have lots of mosquitos, cockroaches and ants, since I live surrounded by a big garden. Im happy to keep them around if they are not dangerous. Should i let them be, or relocate them?

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    1. You can let them be. They are not dangerously venomous to people, and are rather shy anyway.

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