Insects and relatives Valentina Cipriani Natalie Sarracino

What are insects? Insects are classified within arthropods (segmented body) that have an exoskeleton that mostly consists of chitin, a three part body (includes head, thorax, and abdomen), three pairs of jointed legs, and 2 antennae. Chitin: complex carbohydrate that makes up the cell walls of fungi and is also found in the external skeleton of arthropods. They are among the most diverse group of animals on the planet and include more than a million described species. Represent more than half of all known living organisms.

Digestion The digestive system of an insect is used to extract nutrients and other substances from the food it consumes. Most of this food is ingested in the form of macromolecules and other complex substances like proteins, polysaccharides, fats, and nucleic acids. Macromolecules: a very large molecule commonly created by some form of polymerization. The macromolecules are then broken down into smaller molecules like amino acids and simple sugars before being used by cells of the body for energy, growth, or reproduction.

Respiration Insects conduct respiration without the use of lungs. Instead, they use a respiratory system that consists of internal tubes and sacs through which gases either diffuse or are actively pumped which deliver oxygen directly to tissues that need it. Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced.

Gas exchange Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange. During continuous gas exchange, oxygen is taken in and carbon dioxide is released in a continuous cycle. Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion rather than physically taking in the oxygen. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest.

Reproduction The majority of insects hatch from eggs. The fertilization and development takes place inside the egg, enclosed by a shell. Some insects use parthenogenesis, a process in which the female can reproduce and give birth without having the eggs fertilized by a male.

Metamorphosis Metamorphosis in insects is the biological process of development that all insects must go through. The two types are : incomplete metamorphosis and complete metamorphosis. Incomplete metamorphosis: The insects change gradually by undergoing a series of molts. An insect molts when it outgrows its exoskeleton. Complete metamorphosis: where the insect changes all in four stages, an egg or embryo, a larva, a pupa, and the adult or imago.

Relation to humans Many insects are considered pests by humans. Insects commonly regarded as pests include those that are parasitic (mosquitoes, lice, bed bugs), transmit diseases (ex. malaria ), damage structures (termites), or destroy agricultural goods. Despite the amount of effort focused at controlling insects, human attempts to kill pests with insecticides can backfire. If not used in the proper way. The poison can kill all kinds of organisms in the area, including insects' natural predators such as birds, mice, and other insectivores.

Insect relatives Insects, centipedes, and millipedes are all in the phylum Arthropoda and are classified as uniramians. Uniramians have jaws, one pair of antennae, and unbranched appendages or body parts. Although insects and their relatives share these characteristics as uniramians their different forms and lifestyles separates them into different categories. Centipedes and millipedes are classified into a separate sub phylum called myriapods meaning many legs. Their different characteristics separate them from insects.

Contrasting the Two InsectsCentipedes and Millipedes (Relatives) Compact BodiesLong Bodies Three part bodiesWormlike Are adapted for flightDo not fly. Stay close to the ground Have 3 pairs of legsFrom legs Go through metamorphosisDon’t go through metamorphosis

Centipedes Contain from a few to more than 100 pairs of legs. Most body segments contain one pair of legs each. Centipedes are carnivorous. Their mouths include venomous claws which they use to catch, stun, or kill their prey usually during nighttime. Usually live under rocks or in the soil. Do not contain a waterproof coating on their exoskeleton. Because of this their bodies loose water easily and they must live in moist or humid areas.

Millipedes Highly segmented body. Each segment contains two instead of one pair of legs each which result from the fusion of two segments in the millipede embryo. Live under rocks and decaying logs. Millipedes are herbivores and feed on dead and decaying plant material. Are fearful, gentle creatures who roll themselves up into a ball to protect themselves when they are bothered. Also defend themselves by secreting unpleasant or toxic chemicals.

Centipedes and Millipedes Cont’ More flattened Cylindrical Long Hind Legs

Reproduction Centipedes Male deposits sperm bundles leaving the female to find them. Some females species abandon their eggs, leaving the newly born centipedes to manage on their own yet some nurture their offspring until they are ready to handle things by themselves. Millipedes Male and female join in mating. All female species remain with their eggs until they hatch and nurture their offspring until they are no longer dependent on them. Both Lay their eggs in underground nests.

Life Cycle Spend the winter as adults in a protected habitat and become active in the spring. During the warmer months, females lay eggs in soil and cover it with a sticky substance to keep them together in clumps of between 10 and 60 eggs. Some species do give birth to living offspring though. They then undergo the Immature stage (larvae), when the centipede or millipede hatches from the egg and looks similar to an adult only smaller with fewer leg bearing body segments. Develop through several molts and stages in which more and more leg bearing segments are produced. Some centipedes go through anamorphy in which each molt adds legs to the body during the larvae stage. Other centipedes go through epimorphy in which they hatch with a full set of 15 pairs of legs. Millipedes develop through about 7 stages in 21 to 25 weeks. Some centipedes can live up to 6 years.

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