Thursday, July 29, 2021

Audouin's Trapdoor Spider


On a recent trip to Northern Arkansas, I was exploring the area around our cabin when I came across a large black spider I was not familiar with. At first, I thought it was a tarantula, as it definitely had the “look” of a tarantula as well as the size. What it lacked though was the furry appearance tarantulas have. The only other thing I could think of was a trapdoor spider, but they are rarely found out in the open, so I wasn’t convinced it was one of those either. I posted images to a Facebook page I follow, as well as a spider identification website I use, and my spider was positively identified as a trapdoor spider. I was excited to have spotted a species rarely seen by people.

Trapdoor spiders as well as tarantulas belong to a group of spiders called mygalomorphs. These are old world spiders with downward facing fangs. Both are similar in body structure and mistakes in identity are common…. which I can attest to. Most spiders we are familiar with have fangs that are fixed side-to-side. They also inject venom that liquifies the innards of their prey. This essentially allows them to slurp up the insides of their meal like an insect slurpee, leaving behind the skin of the unfortunate victim. Trapdoor spiders, tarantulas and their ilk also inject venom to subdue their prey, then proceed to consume their entire meal, skin and all! 

The one I found is a type of cork-lid trapdoor spider, they are difficult to identify at a glance and often require more detailed study to determine species. However, that being said, a resource I located online stated there are two species of trapdoor spiders living in Arkansas. One is Ummidia carabivora and the other is the Audouin's Trapdoor Spider, U. audouini. Of the two the one I found looks identical to U. audouini.  Since there are only two options to choose from in AR, I am going to assume it is safe to say the one I found is indeed U. audouini. There is also a diagnostic feature unique to this species. The third leg has a saddle-like depression (can be seen in the picture to the right). Females are larger than males and may have a 2 inch legspan, both are glossy black, with some males having a brownish colored abdomen. 

With over 50 species, trapdoor spiders in the genus Ummidia are widespread throughout the Eastern and Southern United States. Several species occur throughout Missouri but are rarely found by humans except under the right conditions. Typically, after a heavy summer rain males and females will be forced out of their burrows. Or in times of severe drought, they will leave the confines of the burrow in search of water. They are often encountered at this time in pet water dishes or swimming pool skimmers. Males will wander in July and August seeking mates and may be encountered by us during one of these jaunts. It can be a bit concerning to be faced with a large spider that possesses giant fangs. Surely it must be dangerous, right? These spiders are in fact harmless to humans. The venom they possess is only harmful if you are an insect or other small prey item they typically eat. Otherwise, the venom is no more dangerous than bee venom, however the bite will be painful…after all they have large fangs. Thankfully they are docile by nature and not confrontational. They prefer to scurry away rather than stand their ground. If harassed, they may rear up and show their fangs. This is a pretty good deterrent for us humans, especially those who have a case of arachnophobia. I was able to coax this one onto my hand and it just sat their calm as can be and never once acted threatened or offered to bite.

The burrow these spiders dig is where their common name comes from. They can dig a burrow approximately 5 inches deep, using modified fangs that possess rows of hardened spines made just for the job at hand. The burrow will have an opening approximately one inch in diameter. This opening is covered in grass, moss, dirt, bark, and other debris giving it a cork-like appearance and hinged on one side. This little door so perfectly blends in with the environment it goes unnoticed by even experts looking for them. This cryptic little home offers the spider a safe place to hide and hunt from. They sit by the door as it is held slightly ajar and wait for the vibrations of passing insects and other potential meals. They can sense by vibrations alone how close the prey is to the opening of the lair as well as how big the meal is. Suitable prey is quickly snatched by the spider and dragged into the bottom of the burrow and consumed. The burrow is lined with a thick mat of silk and often located near deciduous woodland edges.

Like many animals in nature, the predator becomes the prey, and this spider is no exception. There are several species of spider wasps that are tarantula and trapdoor spider specialists and seek out the burrows these spiders hide in. These spiders have evolved a way to somewhat avoid predation by these determined wasps. When a wasp is sensed at the opening to the burrow the spider will use its fangs to cut a hole in the door to the burrow to hold it closed, then braces its eight legs against the inside of the burrow and holds on for dear life. Because it really is a matter of life and death for the spider. Should the spider not succeed the wasp will sting the spider and paralyze it. The wasp will then lay one or two eggs on the spider. When the eggs hatch the wasp larvae will feed on the spider until they are ready to pupate, and the spider perishes. A gruesome way to leave this world to be sure.

These are truly one of nature’s most unique spiders, calm by nature and posing no threat to humans. Instead, they provide excellent pest control from the secret lairs they carve out for themselves. If you find yourself faced with one of these beautiful spiders, try to humanely escort it back where it belongs.

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