To obtain needed resources or escape predators, some living systems must move on solid substances, some must move within them, and others must do both. Solids vary in their form; they can be soft or porous like leaves, sand, skin, and snow, or hard like rock, ice, or tree bark. Movement can involve a whole living system, such as an ostrich running across the ground or an earthworm burrowing through the soil. It can also involve just part of a living system, such as a mosquito poking its mouthparts into skin. Solids vary in smoothness, stickiness, moisture content, density, etc, each of which presents different challenges. As a result, living systems have adaptations to meet one, and sometimes multiple, challenges. For example, some insects must be able to hold onto both rough and slippery leaf surfaces due to the diversity in their environment.
Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.
Many living systems send auditory signals to communicate with others, including to attract, announce, or warn. These sounds must be audible to the intended recipient in a variety of conditions, such as in wind, water, and solids. As a result, each living system has specific sounds best adapted to its environment. For example, some birds live in loud habitats, like those alongside noisy streams or in windy areas. These birds use sound frequencies that can be heard by other birds over competing environmental noises.
Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies
Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.
The feet of aphids appear to adhere to surfaces using capillary adhesion.
1=Anaglyph SEM image of Aphis fabae, magnification 50x
“Thus, in an aerial system, water can act as an adequate glue by a mechanism commonly referred to as ‘capillary adhesion.’ Aphids appear to use it to adhere to surfaces (Dixon, Croghan, and Gowing 1990). And it almost certainly helps a tree frog rest placidly on a vertical pane of glass.” (Vogel 2003:428)
“1. The adhesive force acting between the adhesive organs and substratum for a number of aphid species has been studied. In the case of Aphis fabae, the force per foot is about 10 µN. This is much the same on both glass (amphiphilic) and silanized glass (hydrophobic) surfaces. The adhesive force is about 20 times greater than the gravitational force tending to detach each foot of an inverted aphid.
“2. The mechanism of adhesion was considered. Direct van der Waals forces and viscous force were shown to be trivial and electrostatic force and muscularforce were shown to be improbable. An adhesive force resulting from surface tension at an air-fluid interface was shown to be adequate and likely.
“3. Evidence was collected that the working fluid of the adhesive organ has the properties of a dilute aqueous solution of a surfactant. There is a considerable reserve of fluid, presumably in the cuticle of the adhesive organ.” (Dixon et al. 1990:243)
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