A Hobbyist’s Guide to Spiders

kingdom Animalia > phylum Arthropoda > class Arachnida > order Araneae

Perhaps some of the most loathed but ultimately invaluable creatures on the planet are spiders. The 45,000+ species of spiders are found on every continent with the exception of Antarctica. Contrary to popular belief, spiders are not insects but in fact belong to the class of Arachnida, which also includes ticks, mites, and scorpions. Unlike insects, spiders transport themselves on eight legs instead of six, bear no antennae, and have bodies which are segmented into two parts rather than three. In addition, unlike most other members of the phylum Arthropoda, spiders do not have extensor muscles, and stretch their limbs using hydraulic pressure.

A spider’s body is composed of two parts joined by a cylindrical pedicel. The cephalothorax consists of the head and the thorax, and contains the central nervous system, a massive cluster of ganglia forming a brain, and venom glands. All of the spider’s eight limbs are connected to the cephalothorax. A pair of appendages called pedipalps, which perform a similar role as an insect’s antennae, are attached to the front part of the spider’s head. In addition to serving as taste and smell organs, palps in male individuals are also used to transfer sperm during mating. The abdomen is the hind part of the spider and carries out life functions such as breathing through book lungs (stacks of alternating air pockets and tissue filled with hemolymph, the arthropod equivalent of blood), digestion of liquid nutrients, and secretion of silk from up to six types of glands. Each gland produces a different variation of silk – for example, sticky, rigid, or stretchy. Spiders incorporate some or all of their available silk types into the architecture of a single web. Due to the inability to take in solid food through their intestine, spiders inject their prey with digestive enzymes to liquidize internal structures. The abdomen of female individuals also holds the ovaries.

Generally regarded as a carnivorous species, spiders have developed a multitude of hunting methods from the time they evolved silk-producing spigots about 386 million years ago. The spiral orb web appears to be one of the earliest forms of trapping insects in midflight, and is largely used by spiders with poor vision who are extremely sensitive to vibrations. Argyroneta aquatica spiders, who spend their entire lives underwater, construct “diving bell” webs, which they fill with oxygen and use as a gill around their abdomen. Female Cladomelea debeeri spiders, better known as bolas spiders, walk a single strand of web and swing sticky obs of silk to capture moths and moth flies in the air. Tarantulas and members of the primitive Liphistiidae family are categorized as ambush predators, who hunt by lurking in burrows surrounded by a network of silk threads. Several species of spiders do not use webs at all, and instead pounce on or chase prey over short distances. These include wolf spiders, crab spiders, and jumping spiders, the latter of which possess characteristic large round eyes and account for over 13% of all spider species. Jumping spiders of the genus Portia use remarkably intelligent tactics to hunt other spiders, outflanking them or luring them from their webs. Yet another highly evolved hunting strategy of jumping spiders is mimicry, in which they go to great lengths to imitate various species of ants by developing slimmer abdomens, waving their front legs in front of them to mimic antennae, and hiding their multiple simple eyes by developing large color patches on their head. Pictured below is the Sarinda spider impersonating a Formica field ant.

Evolution has produced two types of web-dependent spiders – the orb-weaving group, who produce flat horizontal or vertical webs, and the tangleweb spiders, which are 4 times as abundant as their counterparts. The difference in population numbers may be attributed to the sphecid wasp, who prefers to snatch spiders off flat webs instead of entering tanglewebbed burrows. Following the instruction manual preprogrammed into its brain, an orb-spinning spider can weave its elegant trap fairly quickly. Non-sticky rigid silk serves the purposes of intersection and absorption of momentum when the web is hit. Sticky threads are designed to entangle prey and give the spider enough time to scamper along the non-sticky strands to the victim. The usual hub of orb webs is offset slightly above the center, as spiders move downwards faster than upwards to reach prey. Half the insects that hit vertical webs escape, and the success rate is even lower in horizontal webs as they are visible to insects in flight and more susceptible to rain and falling debris. There are however, fair advantages to horizontal webs, such as reduced vulnerability to wind damage and the capability to capture insects in vertical flight. In comparison, tangleweb spiders weave irregular, 3-dimensional webs popularly recognized as cobwebs. The 2200 species of tangleweb spiders belong to the Theridiidae family and have a substantial range of web architectures. The general evolutionary trend seems to be progressing into the direction of reduced sticky silk usage in webs, leading to the complete absence of sticky silk glands in certain species.

The majority of spiders’ predators, such as birds and parasitic wasps (as well as humans) have excellent color vision. A spider’s coloration is camouflage from these predators, and many spiders are of the same color as their most common surroundings. Distinctive warning coloration can be found on venomous individuals to discourage attacks. Members of the family Theraphosidae, which includes tarantulas and baboon spiders, use their legs to flick urticating hairs from their abdomen toward their attacker. These bristles are tipped with barbs which cause acute irritation upon contact. The Carparachne aureoflava spider of the Namibian desert prefers to flee when under attack, flipping onto its side and cartwheeling across sand dunes at a rate of 44 revolutions per second, the equivalent of a car driving at 300km/h. Most spiders are timid, nocturnal creatures, and solve conflicts by running away.

Nearly all spider species are venomous, but only a handful have fangs (chelicerae) that are long enough to puncture human skin. Spider bites are an unusual class of injury and the majority of such encounters go unnoticed or cause medically trivial symptoms such as itchiness, nausea, and headache. Fatalities are extremely rare. Out of more than 45,000 species, only 200 (0.4%) deliver medically significant bites. With the exception of web-building spiders that may feed on any soul that its web ensnares, spiders generally do not attack creatures larger than themselves. Most bites occur defensively, when spiders get caught up in clothes or bed sheets and humans unintentionally press up against them. The chemical cocktail that is spider venom can be separated into two groups – cytotoxins/necrotic agents which inflict damage to the tissue, and neurotoxins, which affect the nervous system. Necrotic venom causes blisters to form around the bite, occasionally leading to ulcers and tissue death if untreated. Loxoscelism, a notorious condition caused by the necrotic venom of a recluse spider (genus Loxosceles), is characterized by the premature death of living tissue via autolysis, or self-digestion. Neurotoxic chemicals on the other hand act on the nervous system, causing cramps, rigidity, paralysis and in rare cases, respiratory and circulation failure. The venomous bite of a widow spider (genus Latrodectus) results in Latrodectism, an illness where muscle rigidity, vomiting, and excessive sweating are the predominant symptoms. Prompt medical attention should be sought after the bites of widow and recluse spiders, Australian funnel web spiders, and Brazilian wandering spiders, as these bites may develop into emergencies if antivenom is not administered. In nearly all other cases, spider bites heal without any medical intervention. To become familiar with the 7 most dangerous spider species, click here, and to access detailed information on 39 common species in North America, click here.

jumping spiders like to wear water droplets as fancy hats~