Stinging and Injection Devices of Animals

Cases of convergent evolution

What qualifies as a sting and what had better be called a bite is not always clear and most people say they’ve been bitten by a mosquito while some refer to the “bite” as a “sting”. If the sharply pointed end of a structure is pushed into the tissue of another individual, I think we should call it a sting  –  and stinging animals abound. The stinging devices in animals are amazingly diverse and although we tend to think immediately of the defensive stings of bees and wasps, stinging is also used to deposit, for example in female parasitic wasps, their eggs into caterpillar or spider hosts on whose tissue the larval baby wasps can feed. Injecting venom can be the fastest way to immobilise prey and some stinging animals like, for example the fish-eating slowly moving cone shells or some spiders and snakes that inject venom into their victims, make use of their stinging devices in this way. To obtain oxygen under water without having to come up to the surface, the larvae of the mosquito Mansonia spp. impale the air-containing cavities in the stems of underwater plants with their syringe-like “stinging” syphons.

Venomous snakes, depending on the species, have two ways of delivering the venom to their victims. In those with venom glands connected with teeth at the back of the mouth, the teeth are not hollow, but possess a narrow groove on their inner side, in which the venom runs along. More dangerous are the hollow front teeth of some snakes. These teeth are normally folded up and tucked away under the roof of the mouth when not used, but when needed they point forward to strike the prey and to deliver the venom through tiny pores at their tips. The bite is carried out with a considerable force and the venom is forced from its storage glands into the wound of the victim. A rather similar method is employed by spiders, which also inject venom through a canal inside their two oral appendages, known as chelicerae. The chelicerae have very pointy tips with a hole at the end and the venom stems from the glands at the base of the chelicerae or from deeper in the head. How a droplet of the liquid venom can be pressed through the very narrow tube in the hollow chelicerae and then leave through the tiny pore at the end is something for scientists interested in fluid mechanics and involves some knowledge of the viscosity of the venomous liquid. In most web-building spiders the two chelicerae work like pincers, but in the often much bigger mygalomorph spiders the chelicerae work in parallel striking prey like 2 axes from above.

Similar fluid mechanical problems would apply to the venom delivery of wasp and bee stingers, for they resemble hypodermic needles. The honey bee stinger is barbed (a bit like that totally unrelated stinger of the stingray) and stays in the flesh of a stung human, leading to the death of the bee, but continues to pump venom by itself for some minutes. Wasp stingers and those of some powerfully venomous ants like the Australian bull ant are smooth and can be used repeatedly. Giant centipedes are feared because of their strong mandibles, sometimes referred to as ‘fangs’, which possess a canal through which a venom can be injected into a bitten individual. However, stingers delivering a potent venom that can kill are known not from centipedes, but scorpions. The most dangerous stinging animals in the sea are probably the already mentioned cone shells with their single hollow chitin tooth connected to a venom bulb, further the so-called stone fishes and some others with venomous fin rays as well as stingrays (the death of Steve Irwin comes to mind). The only “stinging mammal” is the male platypus with its venomous and hollow hind leg spurs. But who’d want to pet or even have a chance to pet a platypus?

© Dr V.B. Meyer-Rochow and, 2020.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content. 

biology zoology blog benno meyer wrinkle

“Wrinkle-wrinkle, au revoir”

How I wonder what you are

I have recently been reading about wrinkles. Not because I am worried about my wrinkles (I actually think wrinkles can make a face look more interesting than if it was “as smooth as a baby’s bottom”), but because so many people here in East Asia seem terrified of getting wrinkles and avoid an exposure to direct sunlight through face masks, parasols, summer hats, lotions, creams, etc. The scientific literature on wrinkles includes information on skin structure and function, biochemical and physiological reasons to develop wrinkles, but I couldn’t find anything about perhaps the most obvious reason: you get older, you shrink!  As we age, our height diminishes. During the time I passed university examination I was 184 cm tall; now I am 181 cm tall. People who have spent some time in the space station circling around our planet Earth under zero gravity conditions reverse that trend and are a little bit taller when they return to Earth. An apple that ages shrinks and becomes wrinkly. And humans  – how about us?

Wrinkles consist of more or less deep furrows and bulges and they usually develop along locations of microlines in the skin. The latter form a polygonal network of fine lines easily visible on the outer skin layer (the epidermis) with a magnifying glass. Under the epidermis lie the dermis and hypodermis with their stabilizing connective tissue component proteins collagen for structural integrity and elastin for flexibility and plasticity. And, not to forget, there is hyaluronic acid in the skin with its multiple functions. All the skin layers are associated with underlying lymphatic vessels along with perilymphatic and subcutaneous fat tissue, known as panniculus adiposus and p. carnosus. What is most damaging and a cause of the skin to age is oxidative stress, in other words free oxygen radicals. These radicals are highly reactive and may be produced by the breakdown of double-bond fatty acids following an exposure to UV-radiation. There are, of course, ways the skin tries to protect itself: a higher sebaceous gland density of the skin is correlated with shallower wrinkles, but as the pillars of the skin (like collagen and hyaluronic acid) slowly diminish and the skin becomes drier the decline in skin cell renewal of older people can only be slowed down with a nutrition that is rich in vitamins and anti-oxidants.

What matters also are the genetic factors and how rapidly a person ages. In addition, smoking and heat are often mentioned as wrinkle-promoting, and so is lack of sleep; in fact, anything that causes skin to become dehydrated. However, there is one cause that is related to facial expressions.  Grooves on the forehead during thinking, or wrinkles during laughter, or the vertical lines between your eyes during squinting to see more clearly: such lines can become permanently visible as expressive wrinkles. There is generally not terribly much that an ageing person can do to avoid getting wrinkles, but there is one dog breed (the “Shar-pei”), in which the wrinkles disappear with age. For other and much bigger animals with wrinkled skins, the wrinkles can actually be an advantage as they can hold moisture that can then evaporate from a larger surface area and in this way lead to the cooling of the wrinkled individual. This suggestion has often been advanced to explain the folds and wrinkles of the skins of elephants and rhinoceroses. However, fact is that any animal (other than a Shar-pei dog) develops wrinkles as it ages, especially around the joints. But because animals are covered in fur we tend to overlook their wrinkles  -with one exception: the beautiful, pain-free naked mole rats. Their incredibly wrinkled bodies help these subterranean, naked rodents to turn around in their narrow tunnels and navigate corners with ease.

To return to my earlier statement that we shrink as we age and that space travellers are taller when returning to Earth: my hypothesis is that they would not only be slightly taller but also less wrinkled (provided they got enough sleep and had good vitamin-rich food while at the space station). In any case: Every wrinkle has a story to tell and as for me, there will be a lot more stories when I’m older.

© Dr V.B. Meyer-Rochow and, 2020.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content. 

Strangest Creature on Earth

Not a fungus, plant or animal but behaving intelligently

I learned about these strangest of all organisms already at high school from my teacher Dr W. Ruppolt. And how long ago that was, you can guess from the following comment. At that time slime moulds were seen as organisms straddling the boundary between plant and animal life. They were placed into a separate category of fungi and in those days fungi were considered plants without chlorophyll. It’s all changed: fungi are now regarded as a phylum separate from plants and animals. The slime moulds are neither fungi nor plants and whether one can call them ‘animals’ is also more than doubtful. So, like other unclassifiable organisms they are now called “Protists”. They have, however, amazingly interesting characteristics and this is why they have attracted so much attention in recent years.

There are basically two somewhat similar but evolutionarilly most likely unrelated types. Some, like Dictyostelia spp., start their life as single cell amoeba that crawl around on rotting logs, enter crevices, multiply by fission and feast on bacteria and other minute foodstuffs. If food becomes scarce the amoebae produce signal chemicals which “call together” the individual amoebae from all the nooks and crannies they are hiding in to form what is appropriately termed “a slug”. These whitish usually no more than 10 mm long “slugs” crawl along to find an open, elevated and lit place, where they create a stalked “fruiting body”. Some amoebae sacrifice themselves, die and become the hardened vertical stalk, while others transform into spore-producing individuals at the tip of the stalk, i.e. the fruiting body. The spores are distributed by the wind, then turn into amoeba and the cycle can begin anew.

The other group of slime moulds contains the plasmodium-forming Physarum polycephalum (from physa = pustule and polycephalum = multiheaded). Chances are you’ve seen the species on rotting logs as branched, sometimes spiderweb-like yellow strings, but did not pay much attention to this feature of Nature. Perhaps you should have, because what you see best in autumn is the plasmodium of the organism. A plasmodium can be described as single gigantic cell with multiple nuclei, but no cell walls or membranes present. Plasmodia move around by “streaming”, which is a process in which an inner less viscous sol-like substance is surrounded by the somewhat tougher outer gel-like material, containing actin filaments. Streaming involves rhythmic and erratically changing movements of the plasmodium and a speed of 1 mm per second can be reached. The size covered by a plasmodium fully spread out may be as extensive as a metre (but usually is much smaller). During this plasmodial phase the single cell, but multinucleate “super organism”, engulfs small edible particles and bacteria and avoids bright light, especially blue and UV. The organism has a keen chemical sense and is guided unerringly to a food source (it loves oats and sugary substances, but avoids salt and caffeine).

Why this organism has received such a lot of attention is its ability to move around, to solve problems, to learn and to memorize things  –  all without a brain and differentiated tissues! This organism has led scientists to re-define “intelligence” and its ability to find the shortest escape route in a maze or to connect different food deposits in the most effective way has intrigued researchers no end. In order to sporulate, the plasmodium re-organizes itself to form an often quite colourful fruiting body, from which spores are released. Some of the spores are amoeboid and can crawl along while others are flagellate (possessing flagella). The two kinds of spores are apparently interconvertable. I guess by now you will have become so attached to these “slimeblobs” that you may wish to own one as a pet. If that’s the case get some advice from here.

© Dr V.B. Meyer-Rochow and, 2020.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.