Friday, October 3, 2014

Another Trapdoor Spider

I recently unearthed another Trapdoor Spider.  I believe this is also a Ummidia species, probably the same as the one I dug up last year.  This individual was smaller than my previous find and might be an immature specimen.

Note:  I’ve since been informed that the spider is actually an Antrodiaetus species that constructs a folding door as opposed to a hinged trap door.  See the addendum at the end of the post for additional information.

When disturbed, the spider tucked in its legs and remained still.  It maintained this attitude as long as I was nearby.  Even when picked up, it stayed immobile.  Only when I backed away did it extend its legs and begin to crawl.

The eyes sit atop the head in a short turret arrangement.  These spiders are ambush hunters that leap from their burrows to snag passing insects.  I imagine it would be important for the eyes to be positioned so that the spider could see through the slightest crack made by lifting the protective lid covering the spider burrow.

The chelicerae, those thick appendages protruding from beneath the head, are primary mouth parts used to capture prey.  The bulky portions visible in the photo are the muscle and each is tipped by a fang.  As the muscle portion lifts, the fangs are extended and thrust downward into the prey.  The prey is then pulled into the burrow for consumption.  Venom injected by the fangs quickly subdues the victim.  The attack and capture can be completed in a fraction of a second.

Besides the smaller size, the most noticeable difference between this spider and last year’s is the size of the pedipalp, the leg-like appendage located beside the mouth.  In the larger spider, the pedipalp was quite noticeable from above and looked much like another leg.  To find the pedipalp in the smaller spider, I had to tip it and get a view from beneath.  In the photo above, the head is to the right and you can count the bases of four legs before coming to the downward curving pedipalp.   I’m assuming that the pedipalp will get longer as the spider matures.

The spider was unearthed here at the site of the Toad Pool Project Phase 2.

Vegetation on the site looked much like this before it was stripped away.  Classic Kentucky 31 Tall Fescue made up more than 50 percent of the ground cover.

Fortunately, the spider qualified for the Blue Jay Barrens Disaster Relief Program and was furnished with a new home.  Because of ongoing drought conditions, the ground had to be soaked with water in order to soften it up enough for burrow construction.  The spider’s small size required a pinky finger sized burrow.

The spider wasted no time scrambling into its new retreat.

I came back about an hour later and found the spider applying webbing to the burrow entrance.  My substitute burrow probably doesn’t meet Trapdoor Spider specifications, but I’m hoping it’s close enough that the spider can rework it to suit.  I’d love to go out and find a cap on top of the burrow and watch the spider leap from its concealed burrow to capture some hapless prey.

Addendum: Afternoon October 3, 2014.

About 12 hours after posting the above information, I received an email from Rich Bradley, Ohio spider expert currently with The Ohio State University and author of Common Spiders of North America, with information on the correct identification of the above spider.  It is actually an Antrodiaetus species in a group commonly known as folding door spiders.  Instead of an actual lid topping the burrow, there are two panels of web that can be pulled together or spread apart like curtains over a window.  The feature I failed to recognize while trying to make my identification is the slightly darkened, callous-like feature near the front of the abdomen.

That slightly raised area is a sclerite, a patch of hardened exoskeleton.  I had read about this feature, but was expecting it to be much better defined and easily visible.  Of course, now it is easily visible since I know what to look for.

The total length, 17 mm, is right in line for Antrodiaetus.  When I don’t happen to have a measuring device with me in the field, I photograph the subject against a background that I can easily measure later.  The palm of my hand works perfectly.


  1. Good idea using the palm of the hand for later measuring.

    The smaller pedipalps on this one suggest this one is a female, while the larger, more leg-like pedipalps of last year's suggest it is a male.

    1. Hi, Ted. The palm of my hand is distinctively marked and is something that I've never forgotten to bring back to the house with me.

      It turns out that the two spiders represent different genera. Last year's find is Ummidia and the one shown in this post is Antrodiaetus. Both are females.

  2. Hi,
    i happened to find the beautiful pics . . In my opinion this specimen belongs to Atypidae (purse web spiders). I write from Italy where sometimes find Atypus piceus and Atypus affinis. Both Atypidae and Antrodiaetidae bear a dorsal scutum on the abdomen but this specimen has quite large chilecerae and in the fifth photo from top a lobed palpal coxa can be seen. So it is probably an atypid (probably Sphodros since Atypus snetsingeri is khnown mainly from Pennsylvenia).
    By Daniele

  3. Hi, beautiful pics . .
    in my opinion this specimen belong to Atypidae (Purse web spiders). I write from Italy where sometimes happen to find Atypus piceus and Atypus affinis which looks very similar. Both Atypidae and Antrodiaetidae possess a dorsal scutum. But the large chelicerae of this specimen are tpical of Atypidae, moreover in the fifth photo from top a lobed palpal may probably be seen. A lobe on palpal coxa can be found only in Atypidae among mygalomorphae. So it could be Sphodros sp. or (less probably) Atypus snetsingeri.