Cave Arachnids of the LevantJuly 17 2018
Caves impose as series of environmental challenges for the organisms that make these underground cavities their permanent habitat. In the absence of day-light, the loss or reduction of eyes is one of the most common outcomes of evolving in the undergroud. We are exploring caves in Israel in search of Arachnids showing reduction or complete loss of eyes. Our goal is to understand their evolutionary histories and shed light in the processes leading to this iconic cave adaptation.
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Preparation for the expeditions relied heavily on the expertise of our Israeli colleagues at the Hebrew University of Jerusalem. The team led by Dr. Efrat Gavish-Regev and Shlomi Aharon have prepared a detailed schedule of caves for us to explore. Many of these caves have been previously explored and some of our target species have been sampled or observed in previous surveys. For many other caves, we will be searching arachnids for the first time!
Sarach and Namer caves
Two more caves where we found the reduced-eyes funnel-web spider. Could these spiders belong to the same species? Additionally, we found cellar spiders (Pholcidae) and pale colored woodlice (Isopoda). To our surprise, these caves were crowded with visitors, some venturing into the cavern without headlamps or lights of any sort.
Te'omim cave (July 23)
The cave of twins, as it is also known, has been known and visited by locals for centuries. Today, it is popular hiking destination and a boardwalk allows visitors to visit this cave. In spite of the human presence, the most interesting aspect of this cave is the presence of spiders with normal and reduced eyes living in the same cave, almost side by side. During sampling, we keep separated specimens from the entrance of the cave from deeper and darker chambers. We will need to look closer at the specimens in the lab and their DNA to get a glimpse at their evolutionary history.
In spite of being a relatively small country in terms of surface area, Israel has a large diversity of biomes and landscapes. We spent our first weekend in a field station in the Negev desert in southern Israel. During the nights we went out with headlamps and uv lights to look for scorpions and other nocturnal arachnids.
Currently, 21 species of scorpions are known to occur in Israel. While all scorpions have a stinger to deliver venom only a handful of species pose a threat to human life. There is no simple rule to distinguish dangerous from harmless species of scorpions. Luckily, a recently published field guide, co-authored by one of the lead members of our expedition (Dr. Efrat Gavish-Regev), facilitates the identification of these fascinating arachnids Scorpions of Israel Field Guide.
In the photos: Desert gecko. *One of the most dangerous scorpions in Israel; the sting of *Leiurus hebraeus can be lethal if untreated. A harmless species illuminated with uv, (Scorpio palmatus). *Although not as dangerous as *Leiurus, the sting of Buthus Israelis can also threat human life.
Scorpion vs scorpion (July 22)
In general, scorpions are not picky eaters. Their diet consist mostly of insects, other arthropods and occasionally small vertebrates. I have also read that they would eat other scorpions but this was the first time I witnessed such drama. In the photo below we see a black scorpion, the deadly Androctonus crassicauda, in a contorted position pushing its thick muscular metasoma ("tail") into the borrow of an unidentified yellow colored scorpion. From the yellow scorpion we can only observe its metasoma as is being grasped out of the burrow by the pincer (pedipalp) of the Androctonus. The encounter was for the most part static; probably on the wait for the effects of the venomous sting. I left the scene after taking this picture and don't know the resolution of this struggle. With a name meaning "man killer", the species in the genus Androctonus are to be dealt with caution. In opposition to common belief, color is a poor indicator of the seriousness of envenomation caused by scorpion sting. In the second photo and from the same locality, black scorpion which venom is completely harmless to humans: Nebo hierochonticus.
We are used to think of a caves as natural formations. Carved by the geochemical activity of underground rivers, seismic or volcanic activity. In some cases however, abandoned human constructions provide the conditions of darkness and humidity for cave animals to thrive.
This is the case of the ruins of Haruba, where habitations were buried by centuries of sand and overgrown plants, leaving some underground cavities that were eventually occupied by the type organisms commonly found in caves. The entrance is occulted by invasive thorny cactus (Opuntia) and its walls laced with brown recluse spiders (Loxoceles sp.) and ticks (Ixodidae). Still the cave rewarded us with specimens of two target species: the mediterranean whip-spider Charinus ioaniticus and a funnel web spider (family Agelenidae, shown in this post photo). Although these specimens bear eyes, we will be on the look for their blind counterparts in other caves.
Our first cave is a last minute surprise. On short notice we were granted access to the Manot Cave. This cave was accidentally revealed in 2008 and it is notorious for being the site where the fragment of a 54,700 years old modern human skull was discovered. This finding is relevant because it represents the oldest physical evidence of our species journey outside of Africa. The cave is closed to the public and access is restricted for the ongoing archaeological and anthropological research. We are very grateful for the extraordinary opportunity of collecting arachnids in this site. As for cave arachnids we are on for a good start! Few minutes inside the cave and we spotted chalk colored isopods and our first cave dwelling spider, a woodlouse hunter spiders of the family Dysderidae with reduced eyes! Also, Shlomi's keen eyes secured a handful of pseudoscorpions.
Also good news from outside of the cave, we found one of primary target species the harvestman Haasus judaeus. A cousin of the common garden daddy longlegs, this heavily armored, shorter legs species lives under rocks and has minute eyes.
In March 2006, work in a quarry near Ramla in Israel exposed an opening to and underground cavity: the Ayyalon Cave. Scientists found this cave have remained isolated from the exterior for millions of years and revealed a unique community of invertebrates sustained by a microbial activity. Among the unique animals discovered, they found the remains of a rare blind scorpion, named Akrav israchanani. Despite intensive search efforts in Ayyalon and nearby caves, no living specimens of this species have ever been found and it has been suggested the species is now extinct.
The Ayyalon cave is a recent example of the incredible organisms inhabiting the caves from the Levant region, animals from which we know very little if anything. During this expedition, we will be exploring caves in search for spiders, whip-spiders, and harvestmen with reduced or missing eyes and perform genetic comparisons with their eyed, surface-living counterparts. At the same time we will keep an eye open for other interesting cave arachnids and arthropods we will find; and maybe we will stumble over living cave scorpions!