Arctic Life/Arctic Animals/Invertebrates

From Arctic Bioscan Wiki

Invertebrates

99.9% of all animal species on the planet are invertebrates, and there is no exception for this in the Arctic. With a statistic like this, it should come as no surprise that invertebrates, specifically arthropods, are the most common of all animals living in the Arctic.

Cool Facts

Some Arctic spiders spin greenhouses... Expand the tabs below to learn more about the unique invertebrates living in the North.

The Methuselah Moth
A woolly bear caterpillar.

While caterpillars in southern Canada ordinarily reach maturity in just a few weeks, the larvae of the arctic woolly bear, Gynaephora groenlandica, often require 10 years or more to mature. Their extended development is caused by the fact that larvae are able to feed for only a few days each year because temperatures are so low. These caterpillars produce large amounts of antifreeze to protect their tissues from frost damage during the long series of polar winters.

Spider Solarium
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Greenhouses are often used to extend the growing season in southern Canada and some Arctic organisms exploit the same approach to warm their environments. Some Arctic spiders spin a silken solarium to trap a bubble of air. When the sun shines, air inside the bubble heats up and the spider basks in the warmth of its tiny polar greenhouse.

The Plight of the Arctic Bumblebee

Although there are only two species of bumblebees in the High Arctic, their relationships are far from cordial. The queens of Bombus hyperboreus search out the nests of Bombus polaris and kill the resident queen. They then enslave the resident colony of workers and use them to rear their own offspring.

Sperm Mines

Long before humans developed land mines, the males of springtails and some other groups of soil invertebrates developed a unique approach to reproductive success. Instead of seeking out females, they simply attach packets of sperm on slender stalks to soil particles. When a female bumps into a packet, it explodes and the sperm deposited on her body migrates to her reproductive tract, ensuring fertilization of her eggs. Males of some other species take a more active role. When they locate a female, they surround her with a "picket fence" of sperm packets, so she is fertilized as she crosses it!

Warble Flies, Not Warblers
Infestation of warble fly larvae on the skin of a caribou.

The warble fly makes a distinctive buzz when flying and this sound is no music to the ear of a caribou. In fact, they race off madly across the tundra! The reason for their behaviour is not hard to understand. Female warble flies lay their eggs on the rump of the caribou. The larvae burrow into the skin and spend the winter feeding on the fatty layers beneath. In late June, when they have grown to about the size of a human finger, they burrow out, leaving a hole in the hide of the caribou. Although these wounds heal, the scars show that some caribou have hosted up to 350 larvae in their lifetime!

Life Without Males
Rotifers are asexual organisms.

The populations of many freshwater and terrestrial invertebrates in arctic Canada consist solely of females producing eggs that develop without fertilization. The abundance of such asexual lineages is due to their ability to establish new populations from just a single colonist. The colonization of new territories is tougher for sexual species, as new populations can only be established if several individuals of different gender reach a new habitat. As much of the Arctic has been ice-free for just a few thousand years, it is no surprise to find that good colonizers dominate the scene, a fact which helps to explain the abundance of asexuals.

Polar Vampires
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The bloodsucking behaviour of female black flies and mosquitoes does much to explain their low popularity. These insects are surprisingly common in some areas of the Arctic, even where potential blood donors are rare. There is a simple explanation for this fact. While southern biting flies need a blood meal before laying eggs, northern flies do not. Although blood may be a rare treat, northern mosquitoes and black flies have retained their appetite for it, as evidenced by the swarms of flies which surround Arctic birds and mammals on any warm day.

Love Chains
The head of a male fairy shrimp, showing the structures used in grasping the female.

Males of the fairy shrimp, Artemiopsis steffansoni, are very aggressive in guarding their mates. As females approach maturity, they are each clasped by a male who maintains this grasp for the rest of his life. By guarding the female, he aims to ensure the chance of fertilizing her offspring. When females are in short supply, additional males often grasp the first male to form a chain of 3 or even 4 individuals. Even in death the males do not release their grasp, so late in the season females are often seen swimming with the decaying corpse of their first mate!

Quick Change Water Flea
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Daphnia longiremis, one of the common water fleas in Arctic lakes, has a remarkable ability to reconfigure its shape to escape predation. Dwarf forms, reaching a length of only 0.5 mm, occur in lakes with whitefish. Because of their small size they pass through its gill rakers and escape from becoming fish fodder. By contrast, when this water flea occurs with predatory copepods, it reaches a length of 2.5 mm and grows a pronounced helmet. The increase in size and the large helmet provide protection from predation. How does the Daphnia know which shape to adopt? It turns out that it determines its shape by monitoring the levels of waste materials in the water excreted by each of the predators!

Vultures of the Sea
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The polar seas are alive with flesh-eating amphipods. Although they are just a few centimetres long, they can clean a carcass of its flesh in just a few days. If you tumble into the Arctic Ocean, this clean-up squad will ensure that you're reduced to a neat skeleton which would look good in someone's closet.

Packed with Poisons
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Brightly coloured animals often pack a punch. In fact, they are usually poisonous. The Arctic Ocean is home to Clione limacina, a shell-less mollusc that flutters through the water so slowly that it seems an ideal prey for any hungry fish. In fact, the bright red markings on its body signal the fact that its flesh is deadly – a tiny taste is enough to kill a fish.