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Have you ever watched a tiny red ant scurrying through the backyard only to be astounded that the ant seems like a giant when it walks by some much smaller black ants? Such observations have always caused me to wonder how small insects could become. What are the smallest insects out there and just how tiny are they? The answer is actually astonishing, and, like most good answers it just brings up more questions. Most entomologists believe the tiniest living insects are the fairyflies, infinitesimally minute parasitoid wasps which live on or inside the tiny eggs of thrips(well, some fairflies also live inside the brains of other insects, but let’s not think about that right now). Fairyflies are smaller than many single cell organisms like paramecia, amoebas, and euglenas. Dicopomorpha echmepterygis, a wasp from Costa Rica, is an astonishing .13 millimeters in length. Although many of these wasps fly, they are so tiny that they don’t have conventional wings: some of the smaller specimens have long cilia-like hairs which they use to row through the air (the fluid dynamics of which are considerably different for creatures so small).
Fairy wasp with single celled organisms under electron microscope
In fact the wasps are so tiny that the millions of individual cells which make up their tissues and organs have to be very miniscule indeed. In fact, according to physics, the brains of fairyflies should not work. Many of the neural axons are smaller than 0.1 micrometre in diameter (and the smallest axons were a mere 0.045 μm). At such sizes, the electrical action of axons should not work properly. An article on Newscientist describes the basic problem:
…according to calculations by Simon Laughlin of the University of Cambridge and colleagues, axons thinner than 0.1 μm simply shouldn’t work. Axons carry messages in waves of electrical activity called action potentials, which are generated when a chemical signal causes a large number of channels in a cell’s outer membrane to open and allow positively charged ions into the axon. At any given moment some of those channels may open spontaneously, but the number involved isn’t enough to accidentally trigger an action potential, says Laughlin – unless the axon is very thin.
So how do the wasps continue to fly around and parasitize the eggs of other creatures if the electrical impulses of their brains do not work? German researchers speculate that the axons of wasp brains work mechanically rather than electrically. The tiny axons touch each other physically instead of by means of electrical action. If this is correct it means the wasps are analogue creatures with little clockwork minds! If they were any larger or more complex, this would not work, but because of their small size and simple drives, they can manage to operate with slow-moving machine-like brains.
Micrograph of a fairyfly (fairy wasp)
Dactylanthus taylorii
In grade school biology class we learned that plants use photosynthesis to manufacture their own food from light, water, and air. In almost every familiar ecosystem, the plants are somewhere down there at the bottom, dutifully turning out food for every herbivore (and thereby ultimately for everything). It makes the green kingdom seems so virtuous. The plants I wrote about this week as “underworld plants” are no exception–they provide us with nutrition, beauty, drugs, a way to get rid of lackluster emperors, even natural-looking color for unusually pallid shrimps! And it all comes from air, water, and sun.
However the grade school biology explanation does not provide a full picture. There are indeed plants out there that do not pull their full weight. Like a big dirty city, the plant kingdom has its own underworld filled with creepers and stranglers and suckers—and at the very bottom there are outright parasites. Some plants do not “make their own food” and indeed do not contain chlorophyll at all. They leach nourishment out of other vegetation. One of the strangest and darkest of these parasitic plants is Dactylanthus taylorii, the Hades flower, which comes from the forest undergrowth of New Zealand. Naming it after Hades might be unduly generous—the plant should probably be called the cancer flower.
Dactylanthus taylorii: close-up of male flowers (Photo by Helen Jonas)
Dactylanthus taylorii is the only species in the genus Dactylanthus and the taxonomical relationships of that family are anything but clear. The plant grows on the roots of various indigenous trees. It has not roots and no leaves but I connected to its host via a stem. The tree tissue where this stem attaches to the host becomes horribly distorted into a weird burl-like structure. The plants can be male or female and they are most often pollinated by the lesser short-tailed Bat, (Mystacina tuberculata) which the native Maori call by the evocative name of “Pekapeka-tou-poto” however the flowers also produce a nectar which smells like mammalian sweat. This apparently attracts possums who carry pollen between male and female plants (and perhaps did long before the evolution of the unusual short tailed bat—a creature which deserves its own post).
The Lesser Short-tailed Bat pollinating Dactylanthus taylorii
Like many parasites, the Hades flower is cryptic—it makes itself difficult to find. Because of this characteristic, there are aspects of the flower’s life and lineage which remain unknown. However the modern world does not seem to suit Dactylanthus taylorii : botanists estimate there are only a few thousand left in the wild. The plant’s decline is exacerbated by the fact that collector’s value the freaky wooden excrescences which they create. In the future the hades flower may indeed exist only in the hereafter.
Some things are easy to write about. For example, the world’s largest catfish was an effortless topic—what a great fish! There is plenty of information about the animal and its giant size makes it instantly fun and interesting (although the specie’s widespread decline does bring a sense of mounting unease). For a wide variety of reasons, other subjects are considerably more difficult to address. Sometimes the information is unavailable or the data is lurid and upsetting. In a poignant incongruity, one of these troubling topics happens to be the world’s smallest catfish, the candiru, which hails from the Amazon basin of Brazil.
Vandellia cirrhosa
The term itself “candiru” can mean either the species Vandellia cirrhosa, or it can refer to several genera of similar small catfishes. There is apparently even a genus “Candiru”. To put it bluntly the candiru is a vampire catfish. It enters the gills of larger fishes and sucks their blood–well actually, it doesn’t suck the blood as such. To quote “fishbase” an online fish resource, “[The candiru] bites mostly at the ventral or dorsal aorta arteries, and the blood is pumped into its gut by the host’s blood pressure. It does not need any special sucking or pumping mechanism to quickly engorge itself with blood, but simply uses its needle-like teeth to make an incision in an artery.” The candiru is small. Vandellia cirrhosa rarely exceeds lengths of 1-2.5 in (2.5-6 cm) with a width of 3.5 mm (although much larger specimens are known).
The junction of the Amazon River and the Rio Negro, (near Manaus, Brazil) is the principal haunting ground of the candiru. The catfish hides in the sand or mud. When prey swims by—either in the day or at night—the candiru uses its tremendous sense of smell and powerful eyesight to hone in on the other fish’s gills for a blood meal. The Candiru has backwards pointing spines behind its gill covers. It can lock itself into a victim’s flesh with these razor sharp rays.
The…um…Lovely Beach at Manaus, Brazil
The candiru is not picky about its blood source and this has made it one of the most feared fish in the Amazon. It has been known to enter swimming humans through various orifices or through open wounds. Lurid ethnological reports from as far back as the 19th century detail this fish’s intimate depredations of human hosts.
Argh! Drop those in bleach and go wash your hands with holy water!
It is entirely whimsical—even childish—to speculate about whether the catfish is averse to garlic, possesses immortality, has become a hero to preteen girls, speaks with a strong Baltic accent, etc.
