Insects

insects belong to the group arthropods.

An arthropod is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods form the phylum Arthropoda, and include the insects, arachnids, myriapods, and crustaceans. Arthropods are characterized by their jointed limbs and cuticle made of α-chitin and/or calcium carbonate.The arthropod body plan consists of segments, each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80% of all described living animal species, some of which, unlike most animals, are very successful in dry environments. They range in size from microscopic plankton up to forms a few meters long. Arthropods' primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph - analogue of blood - circulates; they have open circulatory systems. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. Their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong.

Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae (bristles) that project through their cuticles. Arthropods' methods of reproduction and development are diverse; all terrestrial species use internal fertilization, but this is often by indirect transfer of the sperm via an appendage or the ground, rather than by direct injection. Aquatic species use either internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother. Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by scorpions.

The evolutionary ancestry of arthropods dates back to the Cambrian period. The group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians (or their constituent clades) in a superphylum Ecdysozoa. Overall however, the basal relationships of Metazoa are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated.

Arthropods contribute to the human food supply both directly as food, and more importantly as pollinators of crops. Some specific species are known to spread severe disease to humans, livestock, and crops.

There are none on my porch.

If you live in a rather warm climate, and you see them in a spot in the direct sun, running around fast and rather aimlessly, looking something like tiny bright red spiders, with round bodies surrounded by many short legs, those are "chiggers".

The main thing I know about them is that they share an annoying habit with ticks: If they get on you, they burrow into your skin, they itch like crazy, and they're hard to get rid of. If they've already dug in, you can't see them, but you know it's them if you have an itchy spot, and when you look at it, it's slightly pink and slightly raised, like a mosquito bite, but it has a tiny, hard, slightly darker, pin-point dot in the center.

Do I sound like I've had my share of them over the years ?

They could also be clover mites. They also prefer to be in the sun and are often found on cement and brick. They're completely harmless to humans.

First of all, there are actually three kinds of critters called daddy longlegs. The common name daddy longlegs is most often used to describe Opiliones, aka harvestmen. Opiliones are arachnids, but not spiders. They have no venom glands at all, and are absolutely not venomous. The nickname daddy longlegs may also refer to a crane fly, which is a true fly and a member of the order Diptera. Crane flies do not pose a threat, either.

Sometimes, the name daddy longlegs is used for another group of arachnids, the spiders of the family Pholcidae. These spiders are also called cellar spiders.

Cellar spiders do have venom glands. However, there is no scientific evidence whatsoever to confirm that their venom can harm a human being. Not a single documented case exists of a person being bitten by one and having an adverse reaction.

Pholcid spiders do have short fangs, but not any shorter than other spiders that have been known to bite humans. The cellar spider's fangs are similar in structure to those of a brown recluse spider, which we know can and does bite humans. Again, there is no evidence or proof to the claim that their fangs are too short to bite a person.

In fact, the show Mythbusters tackled this daddy longlegs legend back in 2004. Host Adam Savage subjected himself to a cellar spider bite, proving that the daddy longlegs spider is indeed capable of breaking human skin. The results? Savage reported nothing more than a very mild, short-lived burning sensation. Analysis of the daddy longlegs' venom revealed it's nowhere near as potent as venom from a black widow spider.

So, you really don't need to worry about daddy longlegs, of any variety.