Arthropoda-Insecta
Insects make up the majority of the kingdom Anthropoda, which also consists of crustaceans and and spiders. There are approximately a million different species of anthropods, most of which are insects. Insects have an exoskeleton, or cuticle, made of proteins that is waterproof. This allows insects to reside in various environments, including land, air, and water. Insects molt, meaning that they shed their exoskeleton periodically, and are vulnerable during the period when they are without their exoskeleton. Anthropoda is divided into four lineages, Trilobites, Chelicerates, Uniramians, and Crustaceans, insects belongnig to the Urinamians. Urinamians are defined by characteristics including two antennae, compound eyes, an un-branching appendix, and jaw-like mandibles. The insect's body is divided into three sections, the head, thorax, and abdomen. Some insects have wings, which usually extend from the thorax and allow the insect to fly without damaging an appendage. Along with the exoskeleton, which also aids in retaining water, insects have adapted to protect themselves in various ways, some of those ways being spraying or emitting chemicals and poisons, and the presence of pincers, stingers, and spikes.
Insects sense their environment mainly through their compound eyes and their antennae. Compound eyes allow the insect to see; they possess numerous different focusing elements and are multifaceted. The antennae are located on either side of the head, and allow the insects to sense, smell, and feel their environment.
Differing species of insects are either endothermic or exothermic, endothermic meaning that energy is absorbed as heat and exothermic meaning that energy is reseased as heat. Endothermic insects have a higher metabolism, and thus require more food than exothermic insects. They are able to thrive in habitats that have changing weather, and the species that possess wings are able to fly longer distances. Exothermic insects depend on their environment to regulate their body temperature. Due to the stable temperatures in water, exothermic insects are usually found in aquatic environments. Insects maintain osmotic balance in their cells by the presence of hemolymph fluid, which aids in assuring that cytoplasm is present in all cells, as well as spiracles, pores that control the amount of water wapor lost during respiration by opening and closing. Insects also control the rate of urination in order to save water, called the antidiuretic and diuretic factors, by means of the gut and the Malpighian tubes of the insect.
Insects have a tracheal system, which allows for respiration and circulation in the insect, and consists of a system of tubes runs throughout the organism to every cell in its body. Spiracles also allow air flow into the cells, and allow gas exchange to occur accurately by absorbing oxygen into the tracheal system and hemolymph fluid. Insects possess an open circulatory system, in which the heart pumps hemolymph fluid throughout the body, distributing oxygen. The fluid is pumped through short arteries and into cavities called sinuses, collectively known as hemocoel, that are located around the insect's organs and tissues.
Different species of insects use various different methods of acquiring food, which can be almost anything, including wood, plants, blood, other animals and other insects. Insects use either the jaw-like mandibles or other puncturing or sucking mouthparts to capture and chew food. Every insect possesses a complet digestive system, where food is processed in a tube that runs from the mouth of the insect to the anus. This tube is called the alimentary canal, which is divided into three sections, which are the foregut, or stomodeum, the midgut, or mesenteron, and the hindgut, or proctodeum. Insects also have salivary glands and reservoirs, located in the thorax. Saliva is mixed with food through movements of the mouth, which breaks down the food. Once food is digested, it is execreted through the anus. Other metabolic waste is removed through the spiracles in the tracheal system in the form of excess gas made during cellular respiration.
The majority of species of insects are able to walk, and many species have six legs, though many do not. Insects ensure their stability when they walk using a movement called static stability, where at least three of the legs are always on the ground, which helps the insect stay balanced. Many insects also have wings, which can come in one or two pairs and can move in unison or separately, depending on the species. The motor-like pattern of the flapping insect wings is a result of a group of neurons called central pattern generators.
Insects reproduce sexually, typically through direct contact of the male and female, with the male placing the sperm directly inside of the female. Some species of male insects leave a sack of sperm on the outside of the female instead of having sex. To attract a mate of the same species insects use a variety of methods depending on the species, including emitting unique sounds, chemicals, and having bright colors on their exterior. Usually, once a female insect is about to lay eggs, it will find a source of food for the offspring to eat once they hatch. Numerous species of insects mate once in during their lifetime, but they can lay a large number of eggs.
