Linnaeus and the animals
Linnaeus was fascinated by how all species were depending on each other in coexistence in nature, especially the animals and their behaviour. “Without the animals the earth would be like dead, but now the dogs hunt the hare, the gadfly the ox, the falcon the dove, the grebe the fish, the stork the snakes, the eagles the chickens, and everything moves quickly.”
In his botanical garden Linnaeus not only grew plants but he also kept different animals. Some were exotic, like monkeys and racoons, but he also had several tamed Swedish birds. In addition to the living animals he had a large collection of stuffed animals and animals kept in alcohol for research and teaching purposes.
In Systema Naturae Linnaeus made a classification of the three kingdoms. For the anmal kingdom he mainly followed the system from 1693 made by the British scientist John Ray, but made some important additions. Linnaeus’ friend Peter Artedi helped Linnaeus with the classification of fishes and some other animals while Linnaeus was, among other things, working with mammals, birds and insects.
The classification of mammals contained many important changes. Linnaeus based his mammal classification on the animals’ teeth instead of on their feet as previous. He also acknowledged the suckling of the young as being typical for the group, which lead to the fact that Linnaeus was the first scientist to refer both whales and bats to the mammals. Earlier they had been referred to fishes and birds, respectively.
Bats are not birds
The bats were for a long time difficult to classify. Originally they were seen as strange birds. They had wings and they could fly, but they definitely differed from the other birds by giving birth to living suckling young. In the 17th century John Ray placed the bats among “the four-feet animals”. Linnaeus followed his example, and noted that the suckling of the young qualified the bats to belong to the group he called the mammals.
The bats are the only mammals capable of flying. They mostly fly at nighttime, and they generally have bad eyesight. On the other hand their hearing is excellent.
To orientate themselves they give up a cry that works as an echo sounder. The signals are reflected by objects in the bat's environment and helps it to orientate. The cries are of high frequencies and cannot be heard by a human ear, but there are detectors that can be used to listen to the bats. With a detector it is possible to distinguish what species of bats one is listening to.
In Sweden 16 species have been seen, but many of them are nowadays uncommon. The Swedish bats eat insects. Recent changes in forestry have changed the insect fauna, which has resulted in a decrease in number in several bat species. One of the most common species in southern Sweden is the brown long-eared bat, which is commonly found in church towers and other buildings. The brown long-eared bat was described by Linnaeus.
In the tropics there are bats with different feed habits. A big group are fruit eaters, flying among the canopies of trees. In this way they disperse the seeds and they can also be important pollinators. Many trees have flowers or fruits adapted to the bats. The trees can for example have light coloured flowers hanging on long stalks, free from the foliage of the tree. In South America there are species of bats living partly or exclusively of blood. Those are called vampires and are named after the myths about Count Dracula from Transylvania.
Insects have their skeleton outside the body
More than half of all species on earth are insects. How did this group of animals become so successful? One important reason is that the insects have their skeleton on the outside instead of inside the body. The outer skeleton efficiently protects the soft inner parts. Other reasons are their adaptations to land life and their ability to fly. Many insects also have two different stages in life, something that is called a ”complete transformation”.
A butterfly for instance, lives both as a crawling larva and as a flying butterfly. These different qualities have together made the insects able to adapt to many different niches in nature and produce many species.
Linnaeus had an eye for small details and described many insect species. In Systema Naturae 1758 he described 50 species of butterflies and 125 species of flies in Sweden. Today we know 113 butterfly and 4070 fly species from Sweden. Already in Linnaeus’ time most of the butterfly species of today were known but not nearly all flies. An explanation is that the attractive and beautiful organisms are often the first ones to be investigated. The plainer organisms often have to wait longer to be investigated.
How are new species discovered today? It is often the case that what was considered one species in the 18th century is today found to be several, rather similar species. Examples of this are the cluster flies.
The cluster fly – a Christmas fly
The cluster fly often moves indoors to hibernate and sleep through the winter. At Christmas, when you go up to fetch the Christmas decorations in the attic, a fly might wake up and start flying around inside the house. It is therefore called the ”Christmas fly”.
The cluster fly is not related to the common housefly but is a kind of blowfly. It is larger and more hairy than the housefly and the larva is living as a parasite on earthworms. The scientific genus name for the cluster fly is Pollenia.
Linnaeus never described the cluster fly even though they must have been abundant in his workroom. Instead his pupil Johan Fabricius in 1794 named the cluster fly. He called it Pollenia rudis. Fabricius, who became a famous entomologist (insect researcher), distinguished only one species. Today nine Pollenia species have been found in Sweden. The newest species was described in 1987.
The cluster fly species are very similar to each other but can be told apart by details in their hairs. They all act in the same way and it has not been easy to separate the species. We will probably find even more cluster fly species in the future. Fly systematics is studied at Uppsala University.