Tag Archives: Arachnida

Friday Fellow: Deathstalker

by Piter Kehoma Boll

The name of today’s fellow may sound intimidating, and it is for a good reason. Scientifically known as Leiurus quinquestriatus, the deathstalker, which is also known as the Omdurman scorpion, Naqab desert scorpion, Palestine scorpion or Israeli scorpion, is considered one of the most venomous scorpions in the world.

800px-deathstalker_28leiurus_quinquestriatus29_6

A deathstalker in Israel. Photo by Wikimedia user מינוזיג.*

The deathstalker is found in arid regions of North Africa and the Middle East. There are two subspecies, L. quinquestriatus quinquestriatus found in Africa from Algeria and Niger to Somalia and Sudan, and L. q. hebraeus found from Turkey to Iran and Yemen. They are relatively large, measuring up to 11 cm in length.

The venom of the deathstalker has been shown to contain a variety of different neurotoxins, including several inhibitors of potassium and chloride channels, which affect the transmission of nervous impulses through the nervous system. Although very painful, the sting of a single scorpion would hardly kill a healthy adult human, but immediate medical treatment with antivenom is always required to avoid any unpleastant consequences. Children, elderly people, or adult people with heart problems or allergies, however, can easily be killed.

One of the toxins, chlorotoxins, which affects chloride channels, has shown potential to be used in the treatment of brain tumors.

Despite its danger, the deathstalker is often raised as a pet. Why? Because humans…

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References:

Castle, N. A.; Strong, P. N. (1986) Identification of two toxins from scorpion (Leiurus quinquestriatus) venom which block distinct classes of calcium-activated potassium channel. FEBS Letters 209(1): 117–121. DOI: 10.1016/0014-5793(86)81095-X

EOL – Encyclopedia of Life. Leiurus quinquestriatus. Available at < http://eol.org/pages/10208954/overview >. Access on January 7, 2018.

Garcia, M. L.; Garcia-Calvo, M.; Hidalgo, P.; Lee, A.; McKinnon, R. (1994) Purification and Characterization of Three Inhibitors of Voltage-Dependent K+ Channels from Leiurus quinquestriatus var. hebraeus Venom. Biochemistry 33(22): 6834–6839. DOI: 10.1021/bi00188a012

Gueron, M.; Ilia, R.; Shahak, E.; Sofer, S. (1992) Renin and aldosterone levels and hypertension following envenomation in humans by the yellow scorpion Leiurus quinquestriatusToxicon 30(7): 765–767. DOI: 10.1016/0041-0101(92)90010-3

Lyons, S. A.; O’Neal, J.; Sontheimer, H. (2002) Chlorotoxin, a scorpion-derived peptide, specifically binds to gliomas and tumors of neuroectodermal origin. GLIA 39(2): 162–173. DOI: 10.1002/glia.10083

Sofer, S.; Gueron, M. (1988) Respiratory failure in children following envenomation by the scorpion Leiurus quinquestriatus: Hemodynamic and neurological aspects. Toxicon 26(10): 931–939. DOI: 10.1016/0041-0101(88)90258-9

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Don’t let the web bugs bite

by Piter Kehoma Boll

If you think spiders are scary creatures, today you will learn that they are scared too. But what could scary a spider? Well, a web bug!

We usually think of spider webs as an astonishing evolutionary achievement of this group of arachnids and a very efficient way to capture prey without having to pursue them. Webs are sticky, resistant, and only spiders themselves can move freely through them. The only problem is that this is not true.

emesaya_feeding

A thread-legged assassin bug (Emesaya sp.) feeding on a spider after invading the spider’s web in the Western Ghats, India. Photo by Vipin Baliga.*

A group of bugs that conquered the spider world are the so-called thread-legged assassin bugs, which comprise the subfamily Emesinae of the assassin bugs (family Reduviidae). As the name implies, the assassin bugs are a group of true bugs (suborder Heteroptera) that are expert killers of other creatures.

During their evolution, the thread-legged assassin bugs seem to have acquired a special taste for spiders and throughout the world they are usually associated with this eight-legged predators. In many cases, such as the one seen in the picture above, the bugs prey on the spiders, having developed the ability to move through the webs. They usually produce vibrations on the web that attract the spiders. Those, thinking that they caught a prey, are lured directly to their death in the legs and proboscis of the terrible bug.

Some thread-legged assassin bugs have, however, found another way to harass spiders: by stealing their food. In the latter scenario, the bugs usually wait close to or on the spider’s web and, when an insect is caught, they steal it from the spider by ripping it off the web. This kind of behavior is called kleptoparasitism, which means “parasitism by stealing”.

But how can spiders avoid this bug nightmare?

Until recently, it was thought that spiders were safe inside caves. Although emesinid bugs do occurr in caves, their association with spiders seemed to be weaker or non-existent there. But new findings are revealing that they pursue our arachnid fellows even to the deepest abysses of Earth.

The earliest cave-dwelling thread-legged assassin bug known to prey on spiders is Bagauda cavernicola, from India. Its spider-eating habits are known since the first decades of the 20th century.

The second species, Phasmatocoris labyrinthicus, was found almost a century later, in 2013, in Arizona, USA. More than only preying on spiders, such as the species Eidmanella pallida that lives in the same cave, P. labyrinthicus seem to have developed the ability to manipulate abandoned spiderwebs and use them to detect and capture prey for their own consumption. Only a single instance of such a behavior has been recorded and the species’s behavior needs further studies.

phasmatocoris_labyrinthicus_eating

Phasmatocoris labyrinthicus feeding on the spider Eidmanella pallida in the Kartchner Caverns, Arizona, USA. Photo extracted from Bape, 2013.

Now, only 3 years later, there are new evidences of more thread-legged assassin bugs molesting spiders in caves. And this time the observations were made in Minas Gerais, Brazil. One individual of the bug species Emesa mourei was seen standing on the web of a recluse spider (Loxosceles similis) while the spider was at the web’s edge. Another specimen of E. mourei was seen feeding on a fly near the web of a pholcid (cellar spider). The fly and the legs of the bug had vestiges of silk, indicating that the bug stole the fly from the spider. Another bug species, Phasmatocoris sp., was observed on a web of the cellar spider Mesabolivar aff. tandilicus. If this species of Phasmatocoris manipulates spider webs the same way that P. labyrinthicus seems to do is something yet to be investigated.

emesa_mourei_eating

Nymph of Emesa mourei feeding on a fly that it apparently stole from a pholcid spider in the cave Lapa Arco da Lapa, Minas Gerais, Brazil. Photo by Leonardo P. A. Resende, extracted from Resende et al., 2016.

With three different and very distant records of thread-legged assassin bugs associated with spiders in caves, it is clear that the poor arachnids cannot get rid of those bugs even if they run down into the bowels of the Earth.

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ResearchBlogging.orgReferences:

PAPE, R. (2013). Description and Ecology of A New Cavernicolous, Arachnophilous Thread-legged Bug (Hemiptera: Reduviidae: Emesini) from Kartchner Caverns, Cochise County, Arizona Zootaxa, 3670 (2) DOI: 10.11646/zootaxa.3670.2.2

Resende, L., Zepon, T., Bichuette, M., Pape, R., & Gil-Santana, H. (2016). Associations between Emesinae heteropterans and spiders in limestone caves of Minas Gerais, southeastern Brazil Neotropical Biology and Conservation, 11 (3) DOI: 10.4013/nbc.2016.113.01

Wignall, A., & Taylor, P. (2010). Predatory behaviour of an araneophagic assassin bug Journal of Ethology, 28 (3), 437-445 DOI: 10.1007/s10164-009-0202-8

Wygodzinsky, P. W. 1966. A monograph of the Emesinae (Reduviidae, Hemiptera). Bulletin of the American Museum of Natural History, 133:1-614.

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Friday Fellow: Giant red velvet mite

by Piter Kehoma Boll

While walking through an Indian market, you may end up finding something like this being sold as food:

Hmm, it looks like some sort of chips or dried seeds. Photo by Pankaj Oudhia.*

Hmm, it looks like some sort of chips or dried seeds. Photo by Pankaj Oudhia.*

It may look as some sort of crispy seed or dried fruit, some local chips, maybe? But they are actually giant mites… edible mites! They are used in India as a medicine, especially to treat paralysis and allegedly to increase sexual drive, a reason for the popular expression “Indian Viagra”.

But this edible arachnids are actually quite cute when alive. Known cientifically as Trombidium grandissimum and popularly as giant red velvet mite, they are fluffy like a piece of velvet, have a strong red color and reach up to 2 cm in length, a record for mites, which usually measure way less than a milimeter.

I would love to raise them as a pet. Wouldn't you? Photo by Brian Gratwicke.**

I would love to raise them as a pet. Wouldn’t you? Photo by Brian Gratwicke.**

As adults, the giant red velvet mites live freely and prey on small animals, mainly insects, and their eggs. The larvae, on the other hand, start their life as a parasite, attaching themselves to another invertebrate, usually an insect, but sometimes an arachnid, and suck their hemolymph (“blood”). Later, this parasitic larva develops into a free-living nymph that abandons the host and begins to live more like an adult.

The genus Trombidium has many species in the Palearctic Ecozone, so if you are wandering in a forest in Europe or Asia, you may find the giant red velvet mite or one of its cousins.

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References:

Southcott, R. V.  1986. Studies on the taxonomy and biology of the subfamily Trombidiinae (Acarina: Trombidiidae) with a critical revision of the genera. Australian Journal of Zoology, 123: 1-116.

Wikipedia. Trombidium. Available at: <https://en.wikipedia.org/wiki/Trombidium&gt;. Access on July 21, 2016.

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