Category Archives: Arachnids

Friday Fellow: Rhinoceros Tick

by Piter Kehoma Boll

Parasites exist everywhere and, although most of us see them as hateful creatures, more than half of all known lifeforms live as a parasite at least in part of their life. And there are likely many more yet unknown parasites around there. Today I’m going to talk about one of them, which is found in large portions of Africa.

Its name is Dermacentor rhinocerinus, known as the rhinoceros tick. As its name suggests, it is a tick, therefore a parasitic mite, and its adult stage lives on the skin of the white rhinoceros (Ceratotherium simum) and the critically endangered black rhinoceros (Diceros bicornis).

A male rhinoceros tick attached to the skin of a rhinoceros in South Africa. Credits to iNaturalist user bgwright.**

Male and female rhinoceros ticks are considerably different. In males, the body has a black background with many large orange spots. In females, on the other hand, the abdomen is mainly black with only two round orange spots and the plate on the thorax is orange with two small dark spots. Males and females mate on the surface of rhinoceroses. After mating, the female starts to increase in size while the eggs develop inside her and then drops to the ground, laying the eggs there.

A female rhinoceros tick patiently waiting for a rhinoceros to come close. Photo by Martin Weigand.**

The larvae, as soon as they hatch, start to look for another host, usually a small mammal such as rodents and elephant shrews. They feed on this smaller host until they reach the adult stage, when they drop to the ground and climb on the surrounding vegetation, waiting for a rhinoceros to pass by and then attaching to them.

Conservation efforts to preserve biodiversity are mainly focused on vertebrates, especially mammals and birds. Rhinoceroses, which are an essential host for the rhinoceros tick to survive, are often part of conservation programs and, in order to increase their reproductive success, the practice of removing parasites from their skin is common. This is, however, bad for the rhinoceros ticks. If their host is endangered, they are certainly endangered too, and removing them worsens their condition. Are parasites less important for the planet? Don’t they deserve to live just as any other lifeform? We cannot forget that nature needs more than only what we consider cute.

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More mites and ticks:

Friday Fellow: Giant Red Velvet Mite (on 22 June 2016)

Friday Fellow: Cuban-Laurel-Thrips Mite (on 28 June 2019)

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References:

Horak IG, Fourie LJ, Braack LEO (2005) Small mammals as hosts of immature ixodid ticks. Onderstepoort Journal of Veterinary Research 72:255–261.

Horak IG, Cohen M (2001) Hosts of the immature stages of the rhinoceros tick, Dermacentor rhinocerinus (Acari, Ixodidae). Onderstepoort Journal of Veterinary Research 68:75–77.

Keirans JE (1993) Dermacentor rhinocerinus (Denny 1843) (Acari: Ixodida: Ixodidae): redescription of the male, female and nymph and first description of the larva. Onderstepoort Journal of Veterinary Research 60:59–68.

Mihalca AD, Gherman CM, Cozma V (2011) Coendangered hard ticks: threatened or threatening? Parasites & Vectors 4:71. doi: 10.1186/1756-3305-4-71

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Friday Fellow: House Pseudoscorpion

by Piter Kehoma Boll

Spiders, mites, harvestmen and scorpions are the best known arachnids among the general public. However, another group that has a lot of species, even more than scorpions, is that of the pseudoscorpions. There is a very good chance that some of them are living very close to you, especially if we think of Chelifer cancroides, the house pseudoscorpion.

A house pseudoscorpion photographed near Toronto, Canada. Photo by Ryan Hodnett.*

The name pseudoscorpion comes from the fact that these arachnids resemble scorpions, except for the lack of the tail. They are also much smaller. The house pseudoscorpion is brown and measures only about 0.5 cm in length and, as its name suggests, likes to live in human residences.

Male house pseudoscorpions defend a small territory with a radius of only a few centimeters. They allow females to enter their territory and, during the mating period, begin the courtship behavior, by which they initiate a dance and lead the female to a sperm sac (spermatophore) deposited on the ground. The female picks the spermatophore with her genital orifice and use the sperm to ferilize her eggs.

A fat one, likely a pregnant female, in Leibniz, Austria. Photo by Gernot Kunz.**

When the eggs are laid, they remain attached to the female genital pore and are covered collectively by a membrane. When the young hatch from the eggs, they are still larvae and remain inside the sac formed by the membrane covering the eggs. The female then secretes a milk-like substance from her uterus and the larvae feed on it. After molting for the first time, the larvae, now first-instar nymphs, leave the mother and, after three more moltings, reach the adult state.

Female feeding on a mite. Photo by Roland Sachs.*

Although it can pass unnoticed most of the time, the house pseudoscorpion is a cosmopolitan and common species living near and insie houses. Its pedipalps, which resemble those of scorpions, are very long and can reach almost 1 cm in length when extended. As most arachnids, they are predators, and their presence in human dwellings can be quite useful as they feed on smaller, annoying creatures, such as mites, bed bugs and booklice.

If you ever find one in your house, be kind and thank them for their service.

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References:

Harvey MS (2014) A review and redescription of the cosmopolitan pseudoscorpion Chelifer cancroides (Pseudoscorpiones: Cheliferidae). Journal of Arachnology 42: 86–104.

Levi HW (1948) Notes on the life history of the pseudoscorpion Chelifer cancroides (Linn.) (Chelonethida). Transactions of the American Microscopical Society 67(3): 290–298. doi: 10.2307/3223197

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Friday Fellow: Cuban-Laurel-Thrips Mite

by Piter Kehoma Boll

Last week I introduced the Cuban Laurel Thrips, which feeds on several fig trees, such as the Chinese Banyan and the Cuban Laurel. Today, we will continue up the food chain and talk about a mite that is a parasite of the cuban laurel thrips. Named Adactylidium gynaikothripsi, I decided to give it the common name “Cuban-Laurel-Thrips Mite”.

The Cuban-laurel-thrips mite was described only in 2011 from Cuban laurel thrips populations in Greece. This is the fourth mite of the genus Adactylidium known to parasitize the Cuban laurel thrips, the other four being Adactylidium ficorum (“fig-thrips mite”), A. brasiliensis (“Brazilian thrips mite”) and A. fletchmani (“Fletchman’s thrips mite”). As you can imagine, in order to parasitize an insect as small as the Cuban laurel thrips, these mites are even smaller, measuring about 0.1 mm in length.

An adult female of the Cuban-laurel-thrips mite. Extracted from Antonatos et al. (2011).

The life cycle of the Cuban-laurel-thrips mite, which is basically the same for all species of Adactylidium, is very bizarre. Adult females feed on the eggs of the Cuban Laurel Thrips. They start their adult life wandering over fig leaves looking for a suitable thrips egg to attack. Once finding one, they pierce the egg’s shell with their chelicerae and attach to it like ticks and start to eat. They feed on a single egg across their entire life. If they are unable to find an egg, they may also attach to an adult thrips as a last resource, or else they die of starvation in a few hours.

Once a female starts to eat, a small group of eggs, usually between 5 to 10, begins to develop inside her. The eggs grow during the first 48 hours after the female attached to the egg, making her double in size and becoming something like a spherical egg sac. The eggs hatch around this time and the mite larvae remain inside their mother. These larvae lack mouth parts, so it is believed that they absorb nutrients from her mother directly through the body surface. About 24 hours later, the larvae turn into nymphs, which remain inactive inside the shed skin of the larva. They also lack any mouth parts.

Female Cuban-laurel-thrips mites attached to eggs of the Cuban laurel thrips. Extracted from Antonatos et al. (2011).

Another 24 hours pass and the nymphs turn into adult mites. They are still inside their mother when this happens. The adults consist always of a single male and several females. This male then starts to copulate with his own sisters, still inside their mother’s abdomen, and, when copulation is finished, they start to tear their mother’s body apart to get free, killing her in the process. Once outside the body, the male dies in a few minutes, never eating anything other than his own mother. The females, on the other hand, start to look for thrips eggs on which to feed, only to be killed by her own children less than 4 days laters.

This entire life cycle may look very insane from our human perspective, but nature was never interested in following our moral rules.

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References:

Antonatos SA, Kapaxidi EV, Papadoulis, GT (2011) Adactylidium gynaikothripsi n. sp. (Acari: Acarophenacidae) associated with Gynaikothrips ficorum (Marshal) (Thysanoptera: Phlaeothripidae) from Greece. International Journal of Acarology, 37(sup1), 18–26. doi: 10.1080/01647954.2010.531763

Elbadry, EA, Tawfik, MSF (1966) Life Cycle of the Mite Adactylidium sp. (Acarina: Pyemotidae), a Predator of Thrips Eggs in the United Arab Republic. Annals of the Entomological Society of America, 59(3), 458–461. doi: 10.1093/aesa/59.3.458

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Friday Fellow: Platine Shield Harvestman

by Piter Kehoma Boll

Beneath fallen logs and rocks or in the leaf litter of forests and gardens around the La Plata River in Argentina and Uruguay, you may find today’s fellow. Scientifically known as Discocyrtus prospicuus, it is a harvestman, a member of a group of arachnids that resemble spiders. As usual among small hidden invertebrates, it lacks a common name, so I coined the term Platine shield harvestman to refer to it.

Discocyrtus prospicuus in Buenos Aires, Argentina. Photo by Nicolas Olejnik.*

The Platine shield harvestman belongs to the family Gonyleptidae, which includes harvestmen with astonishing armored bodies and a prosoma (or cephalothorax) with a triangular shape resembling some sort of shield. It has a dark reddish brown color and two powerful hindlegs armed with several spines.

The Platine shield harvestman is found in several localities of Argentina and Uruguay, but especially in forested areas around the La Plata River and its tributaries. As usually among gonyleptid harvestmen, the Platine shield harvestman is dependent on environments with a considerable degree of humidity.

Different from most arachnids, harvestmen are usually omnivorous scavengers, feeding on dead animal and plant material, and the Platine shield harvestman is not different. In predator-prey relationships, they are usually the prey of other animals, especially spiders, such as wolf spiders that share the same habitat. When facing a large spider that is about to hunt it, the Platine shield harvestman can use a series of defense mechanisms. One of the simplest ways to avoid being eaten is remaining motionless or playing dead, a behavior called thanatosis. When facing an apparently dead harvestman, a wolf spider usually ignores it completely, as if it wasn’t even there. When this is not enough to stop the attack, the harvestman can use additional strategies, such as “showing its butt” to the spider by lifting its abdomen toward the predator and sometimes kicking the spider with its hind legs. Another common defense mechanism in harvestmen is releasing chemicals with a strong and repulsive scent but the Platine shield harvestman does not seem to use it often, at least not against spiders.

Little is known about the natural history of the Platine shield harvestman or of any of its close relatives. As I said several times before, we need more people studying the small creatures that live all around us.

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References:

Costa LE, Guerrero EL (2011) Geographical distribution of Discocyrtus prospicuus (Arachnida: Opiliones: Gonyleptidae): Is there a pattern? Zootaxa 2043: 1–24.

Fernandes NS, Stanley E, Costa FG, Toscano-Gadea CA, Willemart RH (2017) Chemical sex recognition in the harvestman Discocyrtus prospicuus (Arachnida: Opiliones). Acta Ethologica 20(3): 215–221. doi: 10.1007/s10211-017-0264-5

Segalerba A, Toscano-Gadea CA (2016) Description of the Defensive Behaviour of Four Neotropical Harvestmen (Laniatores: Gonyleptidae) Against a Synchronic and Sympatric Wolf Spider (Araneae: Lycosidae). Arachnology 17(1): 52–58. doi:10.13156/arac.2006.17.1.52 

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Friday Fellow: Truncate Trapdoor Spider

by Piter Kehoma Boll

Today I’m bringing you a species that fascinates me and that I was willing to introduce for a while. Unfortunately, there isn’t much information available about it, that being the reason for my delay in showing it here. However, as new information seems unlikely to appear soon, I can only show it with whatever is avaible.

Named Cyclocosmia truncata, today’s fellow is a trapdoor spider found in the East of the United States and sometimes referred to as truncate trapdoor spider. As all trapdoor spiders, it is a mygalomorph spider, such as tarantulas, and lives in a tunnel that it burrows in the ground and that is covered by a trapdoor. Trapdoor spiders in general rarely leave their burrows and hunt prey at night by standing behind the closed trapdoor and waiting for a prey to pass nearby, then jumping out and capturing it.

A truncate trapdoor spider in southeastern United States. Photo by iNaturalist user jimstarrett.*

Because trapdoor spiders are highly sedentary, they are very vulnerable to predators and parasites that can easily find them by locating their burrows. Species in the genus Cyclocosma have developed a fascinating morphological adaptation to cope with that. Their abdomen is abruptly truncated, giving the impression that someone just cut half of the abdomen off. This region of the abdomen is covered by a heavily sclerotized disc. When the spider is not active, it enters its burrow head first and the sclerotized disc fits perfectly to the walls of the tunnel, forming a false bottom that is impenetrable.

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A nice view of the peculiar disc of Cyclocosmia truncata. Author unknown. Photo taken from imgur.com

Not much more is known about the truncate trapdoor spider or its close relatives. They seem to be considerably rare, living in very restrict habitats, and their burrows are so well hidden that it is hard to find them in the wild.

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References:

Gertsch, W. J.; Platnick, N. I. (1975) A revision of the trapdoor spider genus Cyclocosmia (Aranae, Ctenizidae). American Museum Novitates 2580: 1–20.

Hunt, R. H. 1976. Notes on the ecology of Cyclocosmia truncata (Aranae, Ctenizidae) in Georgia. Journal of Arachnology 3: 83–86.

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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.

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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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