Arxiu d'etiquetes: poisonous animals

Venomous and poisonous arthropods: what makes them different?

After talking about venomous mammals, fishes and lizards, ‘All you need is Biology’ brings you this post about venomous and poisonous arthropods. We will try to explain you what makes them different and which arthropods produce some kind of toxic substance (and how they do it). It will probably surprise you!

Venomous vs poisonous animals

Although some people normally use these words interchangeably, they really mean the same? The answer is NO.

A venomous animal develops specialized organs or elements (such as fangs, teeth or stings) to actively inoculate venom inside the body of their victim as an offensive or defensive mechanism. On the other hand, a poisonous animal does not develop these type of organs, but specialized tissues or glands that produce toxins that are released passively as a defensive system; others acquire these substances from their diet. Sometimes, the toxin is not produced in any specific organ, but integrated within body tissues as a defense against predation.

Despite these differences, once in the body venoms and toxins can cause similar damage, which depends on their mode of action, the assimilated amount and the victim’s features. In humans, effects caused by these substances range from irritation, inflammation or redness to severe systemic damage in cases of powerful poisons.

Venomous and poisonous arthropods

Arachnids

Arachnids (subphylum Cheliceromorpha) include two of the better known venomous arthropods: spiders and scorpions. Both groups develop specialized organs to inoculate venomous substances which use either to hunt and defend themselves against predators or potential enemies.

  • Spiders

The specialized organs for venom inoculation in spiders are the chelicerae, a pair of preoral appendices typical of Cheliceromorpha which they use to grab the food. Spiders’ chelicerae, which are fang-shaped, are related to basal venom glands. These fangs have an internal duct that finish in a terminal opening through which venom is released and injected inside victims’ bodies like a hypodermic needle.

Spiders have the most evolved form of chelicerae: jackknife chelicerae. The two parts of the chelicerae come together like a folding knife, and when threatening to attack, the spiders rise the chelicerae and open the angle of the fangs.

Spider’s chelicerae. Public domain image (CC0) obtained from pixabay.

Some of the most dangerous spiders for humans are the Australian funnel-web spiders (genera Atrax, Hadronyche and Illawarra). Their venom is toxic to sodium channels, which results in the massive release of neurotransmitters.

“Funnel web spider” of the species Hadronyche cerberea. Have you noticed the drop of venom in its chelicer?. Picture by Alan Couch on Flickr (CC 2.0).

  • Scorpions

The most distal part of the scorpion tail, the telson (an additional segment found in several arthropods), has become a venomous organ that ends in a stinger. Like chelicerae in spiders, telson in scorpions is related to venom glands that contain toxic substances.

Scorpion of the species Centruroides vittatus, common in the middle of EUA and in the north of Mexico. In red, telson ended in a sting. Public domain image (CC0).

Scorpion venom is usually rich in neurotoxins that alter both the central and the peripheral nervous system of the victim by dissociating the parasympathetic and sympathetic nervous systems. In humans, the effects of their sting vary from intense local pain (with minor inflammation) to cardiac arrhythmias and acute pulmonary edema, like in the Indian species Hottentotta tamulus, which is considered one of the most venomous scorpions in the world.

BE CAREFUL! Neither all arachnids nor related groups are venomous; e. g. harvestmen, camel spiders and whip spiders (Amblypygi) ARE NOT venomous.

From left to right: harvestman (Daniel Jolivet on Flickr, CC 2 .0), camel spider (CC 3.0) and whip spider (Geoff Gallice on Flickr).

Myriapoda

The subphylum Myriapoda is divided in two classes: Diplopoda (millipedes) and Chilopoda (centipedes), and both produce toxic substances.

  • Millipedes

Millipedes, which have an elongated body composed of a lot of segments with two pairs of legs (rarely just one pair), are detritivores and inoffensive. However, they release toxins (alkaloids, benzoquinones, phenols) as a defensive mechanism to prevent predation. Some of these released substances are caustic and can burn the exoskeleton of other arthropods or cause skin and mucous inflammation in bigger animals.

Millipede toxins are produced inside repugnatorial or odoriferous glands and then excreted through small micropores located at both sides of the body when being crushed or feeling threatened.

At the first sight, micropores are difficult to see. Picture by Thomas Shahan on Flickr (CC 2.0).

TRIVIA: black lemurs from Madagascar (Eulemur macaco) grab and bite millipedes to stimulate their secretions, and then rub them all over their body. It is thought that lemurs cover themselves on millipede’s toxins since these work as insect repellent.

If you want to learn some more about this behaviour, don’t miss the following video. We recommend you to stay until the end…the final result will probably surprise you!

  • Centipedes

Centipedes also have a segmented body like millipedes; however, each segment has just a pair of legs. While millipedes are detritivores, centipedes are carnivorous arthropods that hunt their preys actively. To do so, they have developed two large forcipules originated from the first pair of legs which can inject venom contained in glands in the trunk of the animal. They also bite when feeling threatened.

Forcipules of Scolopendra cingulata, by Eran Finkle (CC 3.0).

The Scolopendra genus causes the most severe injuries. However, despite causing an intense pain when stinging, almost all envenomations caused by centipedes spontaneously resolve without complications.

Insects

Despite their diversity, there exist just a few cases of venomous/poisonous insects (class Insecta).

  • Beetles

Some beetle families (Coleoptera order), such as Meloidae, Oedemeridae and Staphylinidae (Paederus and Paederidus genera) contain toxins within their hemolymph which are released by compression as a defensive strategy against predators. These substances cause skin burns, redness and inflammation in humans.

Sptaphylinidae of the species Paederus littoralis, from Spain, France and Italy. Picture by Alvesgaspar (CC 4.0).

Meloidae and Oedemeridae hemolymph contain cantharidine, while the one of Paederus and Paederidus contains pederine, a substance that is exclusive of females of these beetles and of certain marine sponges, and which is thought to be produced by symbiont bacteria.

  • Bugs

Although some bugs (suborder Heteroptera) are better known for being disease vectors, they also cause different types of skin injuries in humans due to the release of caustic and inflammatory substances as a defense when being compressed (e. g. Pentatomidae family) or by the injection of salivary enzymes that are normally used to kill and dissolve preys (e. g. Belostomatidae family).

Belostomatidae. Public domain image (CC0).

  • Hymenopterans

Most of wasps, bees and ants (Hymenoptera order) produce toxins as a defensive mechanism. In most of those cases, females develop a stinger at the end of the abdomen resulting from the evolution of the ovipositor (Aculeata infraorder); however, there are also some groups that defend themselves by biting.

Ants (Formicidae family) usually attack by biting, but some species, such as those in the group of the fire ants (Solenopsis spp.) and the bullet ants (Paraponera spp., Dinoponera spp.), also have stingers like bees and wasps. Formic acid probably is the best-known toxin produced by ants, but is unique to the Formicinae subfamily; fire ants, for example, inject piperidine alkaloids. The sting of the bullet ants, which are distributed throughout center and south America, is considered the most painful sting for humans caused by an insect according to the Schmidt Index (which considers it to be as painful as a gunshot!).

Red ant of the species Solenopsis invicta (left, public domain image (CC0)) and bullet ant of the species Paraponera clavata (right, April Nobile / © AntWeb.org / CC BY-SA 3.0).

Females of most of bees and wasps within the Aculeata group develop an abdominal stinger. Their venom is usually rich in phospholipases, producing effects ranging from local inflammation to severe anaphylactic reactions (when suffering of hypersensibility or after being attacked by thousands of insects, as it has happened several times with the killer bee in America). The sting of the tarantula hawk (Pepsis formosa) from Mexico and southern USA, is considered the second most painful after the one of the bullet ant.

Pepsis formosa, a tarantula hawk. Public domain image (CC0).

  • Butterflies and moths

A lot of butterflies and moths (Lepidoptera order) produce toxins either during their larval stages, adulthood or both as a defensive mechanism against predation.

Sometimes, caterpillars are covered by urticant bristles or hairs that cause skin lesions (erucism), as in the case of the pine processionary (Thaumetopoea pityocampa), a harmful plague for pines which is very spread in southern Europe and America.

Pine processionary caterpillar nest, by John H. Ghent (CC 3.0).

On the other hand, adults of some species, like those of the monarch butterfly (Danaus plexippus) and Zygaena spp., both showing flashy colors (aposematism, a type of animal mimicry), develop toxins within their corporal tissues to prevent predation. The monarch butterfly obtains these substances by feeding on toxic plants of the Asclepias genus.

Zygaena transalpina, by gailhampshire (CC 2.0).

.             .             .

Have you found this information interesting? Do you know any other venomous or poisonous arthropod? Feel free to leave your comments below!

References

The main image is of public domain (CC0) and was downloaded from Pixabay.

Fishes with bad spines

This week, after the amazing success of the last post, I will change the direction of the article and I will focus on the fishes with bad spines, it is, fishes with venomous spines, but focusing on the Mediterranean species. 

INTRODUCTION

Despite seas and oceans of the planet are inhabited by a high number of potentially dangerous animals for humans, understanding its danger for bites, electric discharges or for its consumption; the truth is that in only few cases these animals attack deliberately; so, accidents are that: accidents produced by ignorance or carelessness. We have to have into consideration that we are not a prey of this fishes, so: which is the sense that this animals attack us deliberately?

These fishes with bad spines are catalogued as actively venomous animals, it is, they have a venomous apparatus with glands that produce poison and a mechanism that permits the introduction inside another animal, like spines or teeth. This poison are used to defend themselves or/and to capture their preys.

PREVENTION IS BETTER THAN CURE

These are some tips to prevent possible injuries when you go to the beach or when you are diving. They are useful to avoid venomous fishes and other marine animals:

Prevention at the beach

  • To inform about venomous animal of your destination.
  • Don’t touch anything that you don’t know.
  • Watch your step. There may be sea urchins or fishes…
  • Taking a swim at night or in desert beaches suppose more risk.
  • Use full-body neoprene in waters with potentially dangerous fauna, like Australia.
  • Don’t swim close to the bottom (sand, rocks or reefs).

Prevention while diving

  • Control your flotability in order to don’t touch anything.
  • Don’t put your hands inside cavities, cracks or holes if you don’t see the interior.
  • Leave a exit way for animals.
  • Don’t feed fishes.

MEDITERRANEAN FISHES WITH VENOMOUS SPINES

Myliobatiformes

Description. They include whiprays. Their body is flatten and with a circular or rhomboidal shape. They are the only venomous fishes that can produce a deep wound. The venomous spines are place in the upper part of the tail, with different shapes, sizes and positions according to the family. They usually are on the seafloor (benthonic species), often buried with sediment and with the eyes and spiracles on the water, so the most part of the accidents are for involuntary footsteps.

Danger. In whiprays, the needle is placed far from the the base of the tail, what allows for a wide outreach, but only it is a defensive weapon. The needle is hard and with hooks in the edge. It is in its interior where are venomous glands, which acts on heart muscles. In addition to the wound, the symptoms are: nausea, diarrhoea, vomit, sweating, circulatory disruptions and anxiety.

Mediterranean  species. There are two venomous species in the Mediterranean: roughtail stingray (Dasyatis centroura) and common stingray (Dasyatis pastinaca). Roughtail stingray can measure 210 cm, has a rhomboidal shape and in the central part of the back and in the tail it has bony tubercles. They live in coastal waters, where feed on crustaceans, cephalopods and small fishes. On the other hand, common stingray, that also inhabits in coastal waters, doesn’t have bony tubercles in the back, but in the tail.

Escurçana clavellada (Dasyatis centroura)
Roughtail stingray (Dasyatis centroura) (Picture: Okeefes)

Escurçana o milà (Dasyatis pastinaca) (Foto de Ictioterm)
Common stingray (Dasyatis pastinaca) (Picture: Ictioterm)

Scorpaenidae

Description. With a robust body, Scorpaenidae fishes have big pectoral fins and a wild and big head. Its colouration is brown reddish and irregular.

Danger. Most of the species live on the rocks or behind corals, so the risk is on step on them. The poison produce a reduction of pressure and lung edema and an increase of pressure on lung arteries, and cramps. The hard spines placed in front of the dorsal fin, the three first of the anal fin and the two first of the ventral fins present poison.

Mediterranean species. In the Mediterranean, there is 3 species with venomous spines: the largescaled scorpionfish (Scorpaena scrofa), the small red scorpionfish (Scorpaena notata) and the brown scorpionfish (Scorpaena porcus). The largescaled scorpionfish is the biggest species in the Mediterranean (till 50 cm) and live in rocky and sandy seafloors. It can be easily identified by long dorsal spines with separated membrane. On the other hand, the small red scorpionfish has a short tentacle above each eye, has not appendixes in the chin, its size is about 20 cm and with a black spot in the dorsal fin. Finally, the brown scorpionfish has large tentacles above the eyes and in the chin.

Cap-roig (Scorpaena scrofa) (Foto de Ictioterm)
Largescaled scorpionfish (Scorpaena scrofa) (Picture: Ictioterm)

Captinyós (Scorpaena notata) (Foto: Dein Freund der Baum, Creative Commons).
Small red scorpionfish (Scorpaena notata) (Picture: Dein Freund der Baum, Creative Commons).

Escórpora (Scorpaena porcus) (Foto de Maestro Pescador)
Brown scorpionfish (Scorpaena porcus) (Foto de Maestro Pescador)

Trachinidae

Description. These fishes has a long and laterally flatten body. The mouth is wide and orientated upwards.

Danger. All the species live in sandy seafloors, where bury theirselves. The venomous spines are the 5-7 first of the dorsal fin and the spine in the gill operculum. The poison produce an intense pain in the affected zone and cause sweating, nausea and secondary infections.

Mediterranean species. There are two venomous species in the Mediterranean: streaked weever (Trachinus radiatus) and the greater weever (Trachinus draco). The streaked weever can be identified by: a brown yellowish to gray body with dark spots and the first dorsal fin has six spiny spines. Such can be the gravity of the bite that can be lethal. The greater weever has a grey greenish to brown yellowish body; with short, dark and yellow lines and with 5-7 spiny spines in the first dorsal fin.

Aranya de cap negre (Trachinus radiatus) (Foto de SnipView).
Streaked weever (Trachinus radiatus) (Picture: SnipView).

Aranya blanca (Trachinus draco) Foto de Biopix).
Greater weever (Trachinus draco) (Picture: Biopix).

Rabbitfishes

Description. They are typical species of coral reef and in lagoons in Indian and Pacific oceans, but one species can be found in the Eastern Mediterranean, where lives in rocky seafloors with algae. Its body is oval and very laterally flatten, with a small head and mouth.

Danger. Rabbitfishes are shy, so it is difficult to be hurt by their spiny spines, which are all over the body: 13 in the dorsal fin, 7 in the anal fin and 2 more in the ventral fin. Poison causes a hard pain, but it doesn’t persist so much.

Mediterranean species. The marbled spinefoot (Siganus rivulatus) has an olive light body with irregular brown spots. It can be confused with salema porgies (Sarpa salpa). It is an invasive species.

Peix conill llis (Siganus rivulatus) (Foto: Stephan Moldzio, Fishbase).
Marbled spinefoot (Siganus rivulatus) (Picture: Stephan Moldzio, Fishbase).

Remember: you don’t have to be afraid of sea and nature. With common sense and respect towards nature you won’t suffer any harm.

REFERENCES

  • Ballesteros E & Llobet, T (2015). Fauna i flora de la mar Mediterrània. Ed. Brau
  • Bergbauer, Myers & Kirschner (2009). Guía de animales marinos peligrosos. Ed. Omega
  • Martin, P (1999). Claves para la clasificación de la fauna marina. Ed. Omega
  • Riedl (1986). Fauna y Flora del Mar Mediterráneo. Ed. Omega

Difusió-anglès