Insects and Arachnids
The Insects :
Insects are a class of invertebrate animals of the arthropod shank and the hexapod subbranch. They are characterized by a body segmented into three tags (head with external buccal parts, a pair of antennae and at least one pair of compound eyes; thorax provided with three pairs of articulated legs and two pairs of more or less wings modifieda; abdomen devoid of appendages) protected by a cuticle forming an exoskeleton composed of chitin and provided with respiratory tracheae.
The life cycle of insects goes through several stages of physical transformation called "moults" and generally involves several metamorphoses. Spiders, scorpions and mites are not insects, but arachnids; among other differences, they have eight legs.
Entomology is the branch of zoology whose object is the study of insects.
The bees :
Bees play an essential role in nature. They participate in the pollination of many plant species. Without them, a large number of varieties of plants, flowers and fruits would be doomed to disappear. The bee needs the flower for its pollen, the flower needs the bee for its fertilization (pollination).
For several years, we have witnessed an excess mortality of honeybees. The causes are poorly understood and numerous (pesticides, parasites, etc.). Threats to bees can have serious consequences for agriculture and our environment.
The butterflies :
Lepidoptera are an order of insects whose adult form is commonly called a butterfly. They are characterized in the adult state by three pairs of legs (like all insects) and by two pairs of wings covered with scales of very varied color depending on the species. Lepidoptera lay eggs which give rise to caterpillars. The latter make silk, and then often form a cocoon.
Butterflies are pollinating agents, and therefore have a useful role in nature, although some species are presented as pests for agriculture as caterpillars. They are also prey for birds and other animals.
The 5,200 species of butterflies identified in France therefore play an important role in the proper functioning of the ecosystem balance. By their natural beauty, butterflies are able to generate a popular craze for the protection of natural sites.
The Dragonflies :
Odonata are an order of insects, often called a dragonfly, with an elongated body, endowed with two pairs of generally transparent membranous wings, and whose compound and generally large eyes allow them to effectively hunt their prey. Their larvae develop in the water, during the beautiful season this metamorphoses into a flying insect called "imago".
Odonates group two sub-orders: zygopters and anisopters:
- The anisoptera or dragonflies in the strict sense have the wings extended flat at rest, not petiolate and uneven, the anterior are narrower than the posterior, often contiguous eyes, rapid flight.
- Zygoptères or demoiselles with the fine body, have the identical front and posterior wings, maintained along the body at rest, a head wider than long, eyes widely separated. The flight is not very fast and at rest, the wings are joined and raised above the body.
In damselflies or zygopters, there are:
- Caloptéryx, with metallic colors and colorful wings.
- Agrions, small often with blue or red.
- The lestes, often metallic green or brown.
43 dragonfly species are listed in the Camargue out of 83 listed in France. (source PNRC de Camargue 2005). Almost all of the photos presented on the site were taken in the Camargue.
Arachnids are a class of chelicerate arthropods, terrestrial or aquatic, often insectivorous. This is the group that includes, among others, spiders, scorpions and mites. They are distinguished within the branch of arthropods by the fact that they have four pairs of legs, that they have neither wings nor antennae, and that their eyes are simple (ocelli) and not composed. Most arachnids are oviparous and the sexes are generally of different morphologies (sexual dimorphism).
Common parlance often considers spiders to be insects; for the zoologist, they are distinguished from these by the number of legs: eight in arachnids, six in insects.
The spiders :
Spiders or Araneids (order of Araneae from the Arachnid class, to which it gave its name) are arthropod invertebrate predators. Like all chelicerates, their body is divided into two tagmes, the prosome or cephalothorax (anterior part devoid of mandibles and antennae, with eight legs) and the opisthosome or abdomen which carries at the back the spinneret. They secrete by these appendages silk which is used to produce the wire which allows them to move, to weave their canvas or cocoons trapping their prey or protecting their eggs or small, even to make a temporary reserve of sperm or a dome their allowing air to be stored under fresh water. Unlike insects, they do not have wings, antennae or chewing parts in the mouth. They generally have six to eight eyes which can be single or multiple.
As predators, spiders play a major role in regulating insect populations, and they are themselves regulated by often specific predators including:
- insects, with in particular wasps, including all pompiles wasps exclusively predatory of spiders, which they bite precisely at the level of the nerve centers by paralyzing them before taking them to the breeding site of the larvae, as well as the wasps masons who build earthen urns which they fill with small paralyzed spiders (which will be used to feed their larvae),
- many reptiles,
- some amphibians,
- many birds said to be insectivorous or more general including almost all the birds eating close to the ground or on the ground (thrush, wagtail, robin, wren, etc. up to the heron, via pheasants, hens, guinea fowl, partridge...),
- some mammals, including bats, hedgehogs, foxes or mustelids (including weasel, weasel ...).
The sericogenic glands produce silk spun by small articulated protuberances (dies), most often 6 in number, located on the ventral side more or less at the end of the abdomen. The silk is liquid in the glands, but solidifies into fibrils once exited by the fusules, under the effect of the traction exerted by the legs of the animal and in contact with the air. The silk thread is in fact constituted by an interlacing of a high number of elementary fibrils, of 0.05 μm in diameter each. The diameter of the silk thread varies between 25 and 70 µm, (with an equivalent diameter, these threads are deemed to be more resistant than steel and have a shape memory 5 to 12 times greater than latex).
Most species of spiders have venom glands.
The branch of arachnology dedicated to them is araneology.