I spent much of my professional life studying arachnids, especially spiders. I think that I was drawn to them for two reasons. They were comparatively little known and often misunderstood (I have written about this in two earlier diaries on my childhood.) In addition most served as important secondary consumers (carnivores) in many terrestrial ecosystems. My first real interest began when I found a resting sac of Phidippus apacheanus on a desert shrub in the Yuma desert of Arizona when I was about ten years old. It contained a male of this beautiful jumping spider (the males have black legs and bright orange-red dorsal surfaces. They appear to mimic velvet ants.) As a teenager I sent an inquiry about possible pen pals (this was around 1960 — there was no Internet) to Alice Gray at the American Museum of Natural History in New York City. I mentioned jumping spiders as an afterthought. She put me in contact with a young man who was interested in these creatures and I am still in contact with him and his associate, to whom I also wrote and with whom I coauthored several publications. Between them I became hooked on these fascinating spiders, although eventually I also conducted research on violin spiders, wolf spiders, various families of sac spiders, as well as scorpions- the latter mostly in aid of a specialist I knew. I became a charter member of the American Arachnological Society in 1972 and am a member to this day.
Almost all arachnids, other than a number of mites, are predatory. Ticks and some other mites are parasites and a few arachnids (some spiders) other than mites will feed at least occasionally on nectar and/or pollen. Some mites (such as spider mites) are totally plant feeders. The following photo essay will sample some of the predatory species, but because of the complexity of the class Arachnida. this can only be a tiny sample. There are, for example, over 5000 species of the largest spider family (and my favorite) the Salticidae or jumping spiders. There are more than 100,000 species of all arachnids and their variety is quite phenomenal. Even though most are predators, studying their methods of prey capture and their varied biologies, mimicry, and reproductive behavior could easily occupy a battalion of researchers, from taxonomist to ethologists, for several life times.
Scorpions are perhaps the least appreciated of arachnids, after ticks. They do not spread diseases, but do have a venomous sting. Although my own research centered on spiders, I did spend some time with scorpion specialists collecting scorpions for a research project and even wrote a chapter on them for a book. Scorpions are quite fascinating and they are among the most ancient of orders, dating from as early as the Silurian, 430 million years ago. Scorpions were aquatic then and possessed both compound eyes and book gills, but there is no mistaking the body of a scorpion even then. One neat fact about scorpions is that they glow under a UV light! That is how they are found by researchers as they are foraging at night. We still are not certain if this has a function, or is just a accidental result of waste storage in the cuticle. however no other arachnids have this characteristic as far as I know.
Male scorpions produce spermatophores, which they then attach to the substrate. They then pull the female over the spermatophore so that the sperm inserts into her genital opening. The process of getting the female in place is the famous dance of the scorpions, or promenade à deux. Fabre in his Life of the Scorpion (English translation) missed this and was puzzled by the behavior, especially when he found the female eating the male the next day. In the wild males usually escape, but Fabre kept his scorpions in a cage. I have only observed this behavior once in the wild under UV light above the New Mexico town of Hatch in the early morning hours (the locals probably thought they were being visited by space aliens!) And then I did not see the whole act as my companion wanted to collect the spermatophore.
Female scorpions give birth to live young and even have a structure like the mammalian placenta, except that they are attached by the mouth. The young scorpions climb onto the mother’s back and remain there until they molt. They are then on their own. Looking like miniatures of the adults, they can sting, but do not produce as much venom. Nor is their venom more toxic than that of adults.
I am often asked about deadly scorpions and indeed there are a few that it would be wise to avoid. Especially the North African and Middle Eastern genera Leiurus and Androctonus. Also Buthus (Fabre’s scorpions), Parabuthus, Centruroides (especially in West Mexico), Tityus and a few others, all in the family Buthidae. The venom is usually neurotoxic and that of Androctonus australis has been known to kill an adult healthy male human in hours. The same species is thought to kill about 400 people annually in North Africa. Both Androctonus and Leiurus are unfortunately easily obtainable on the exotic pet market. I have seen specimens of both being sold. Fortunately populations vary as to the toxicity of their venom so some may be “hotter” than others and thus not all individuals are equally dangerous. Also, as with venomous spider bites, scorpion stings may be “dry,” that is contain no or little venom. Still owning one of these is really asking for trouble, including violation of local dangerous pets laws. Finally, owning a breeding pair or a gravid female in the Southwest, where they could become naturalized if they escaped, is really irresponsible. Still the danger of this happening is pretty minuscule compared to traffic accidents or the possibility of being shot.
Other scorpion-like or vaguely scorpion-like arachnids include vinegaroons (Uropygi), whip scorpions (Amblypygi), Pseudoscorpions (Pseudoscorpiones), and Solpugids (Solifugae). All are non-dangerous, despite stories to the contrary, although Pseudoscorpions have venom glands in their pincers (pedipalpi), solpugids can bite, and vinegaroons can spray a mix of acetic acid and other chemicals from two glands at the base of the hair-like tail.
Harvestmen or true daddy-long-legs (Order Opiliones) are especially found in the world’s forests, where they are common predators in the rock and leaf litter. They have no venom but are often confused with the cellar spiders, which do have venom, but usually have chelicerae too small to bite humans. As far as is known the venom of cellar spiders is not especially toxic in any case. Most of the harvestmen have long legs and tend to move in a bouncing manner. They feed on small insects.
Spiders (Order Araneae) form one of the two largest orders, the other being the mites and ticks (Acari). Both orders have at least 40,000 species each. I will not delve into the latter here, in part because acarologists have had their own society for many years and in part because I have spent very little time on these.
Spiders have very strange mating behavior (at least to us) as the males ejaculate onto a sperm web and suck the sperm up into their palpi, applying these to the female’s genital opening like hypodermics during mating. Mating can be a chancy affair as if the female is hungry, the male may become her next meal. Although North American black widows have a reputation for eating their mates, this is only absolutely true for the related Australian red-backed spider. The male of this species actually flips himself into the female’s mouthparts after mating. He is smaller than the female (almost the rule in some families) and serves as a dose of protein for the production of the eggs.
Spiders are usually divided into three suborders. One is found primarily in SE Asia and the Malay Archipelago and the other two are more generally distributed. The two that are found in North America will be briefly discussed here. The Mygalomorphae or Orthognatha, include the tarantulas, trap-door spiders, and several other smaller groups, including one of the most dangerous spiders on earth, the Sydney funnel-web tarantula (Atrax robustus — Family Hexathelidae) of Australia. For some reason we have yet to discover, the male of this species has a very potent venom which affects humans very badly. Being bitten by one is no joke and can easily bring on hospitalization and eventual death. An antivenin has finally been developed, however, and may make the bite less fatal. The other candidate for the world’s most dangerous spider is the wandering spider (Phoneutria nigriventer and relatives), a large South American member of the entelegyne (see below) family Ctenidae. The venom is very toxic and the spiders are quite agressive. Interestingly wandering spiders often dry bite or inject only a partial dose, so some people who are bitten may not think them especially dangerous. As far as I know the more “primitive” Atrax never does this. Fortunately Australia has strict wildlife laws and for some reason the ctenid has not apparently appeared on the market. There are very few ctenids in North America and no hexathelids at all. Our most dangerous spiders are the much less formidable black widows and violin spiders. However, ctenids, including Phoneutria, occasionally show up on banana shipments. The often much more colorful large ctenids in the genus Cupiennius are also found in such shipments, but are much less dangerous with their bite being more bee-sting like.
Most spiders fit into the Araneomorphae (or Labidognatha.) This suborder can be further divided into Haplogynae and Entelegynae, based on whether the females have hardened (sclerotized) external genitalia (Haplogynes usually lack hardened female genitalia, while most entelegynes have hardened female genitalia.) The haplogynes are made up of violin spiders (including the brown recluse), cellar spiders, sow-bug eating spiders, house spiders and a number of others. However they are vastly outnumbered by the highly successful Entelegynae , which constitute the majority of spiders.
The three-clawed entelegynes are mostly web-builders, except for the wolf spiders (Lycosidae) and a few other families. Web-builders use the third claw on the tips of their tarsi to walk on webs. The web-builders include the Linyphiidae, or filmy dome and dwarf spiders, the Theridiidae, or comb-footed spiders (including the black widow and the related brown widow, red widow, white widow and others — all with neurotoxic venoms, however most other theridiids are not dangerous.)
The Araneidae (orb-weaver spiders) and the related Tetragnathidae (spiny-jawed orb-weaver spiders), build the standard wheel-shaped web often associated erroneously with all spiders. Some have lost the web completely and may instead spin a thread with a drop of venom-soaked gum. These are the so-called bolas spiders (Mastophora spp.) The key element is the production of a sex pheromone analog which mimics those of a few species of moths!
Perhaps the most spectacular of the orb-weavers, now in their own family, are the giant silk spiders (Genus Nephila). The webs of these spiders can be as much as a meter or so across and are made of yellowish silk. The webs are so strong that some societies use them to catch small fish. In Florida they are one of the basic components of the summer and fall woodland.
The cat-faced spider (several species in the genus Araneus) can get very common and I have seen webs covering a general store in northern New Mexico. The spiders themselves get fairly large and I have to confess that one scared the daylights out of me when it dropped on a silken thread from the doorway of an abandoned outhouse along the Dry Cimarron River near the Colorado state line. They are, despite appearances, quite harmless.
Although the Lycosidae are mostly hunters on the ground surface (a few build funnel webs) they have three claws like orb-weavers. The eye arrangement, with four small eyes in one row in front, a pair of very large eyes and a third row of eyes in between size, is diagnostic. For the most part these are beneficial and few are known to even bite. Some in the genus Hogna can get quite large- over an inch (25 mm).
The two-clawed entelegynes are primarily non-web-building and hunt by ambush, speed or stalking. These include most of the “sac spiders (several families),” the ground spiders (Gnaphosidae), the various crab spiders (Sparassidae, Selenopidae, Philodromidae and Thomisidae) and my favorite, the jumping spiders. The crab spiders are generally easily identified by having the first three pair of legs facing forward (laterigrade) and are mostly ambushers, the characteristic flower crab spiders (several genera of thomisids) being the most commonly observed.
The jumping spider family (Salticidae) is the largest, comprising over 5000 species. Again, like lycosids, these are easily identified by their eye arrangement, only in salticids it is the anterior median eyes that are the largest, followed by the anterior laterals and posterior laterals, with the posterior medians being tiny. These spiders are varied and while usually box-like in their cephalothorax, they may resemble ants, velvet ants, beetles, grass stems, water droplets, dust clumps or bark. They are diurnal, unlike many lycosids, and highly visual, while also engaging in inaudible (to us) communication. They are expert stalkers of insects and other spiders. Their courtship more resembles that of birds than other spiders, with gaily colored and festooned males strutting their stuff in front of often uncooperative or downright hostile females.
My research over much of my career concerned these remarkable creatures, which are wonderful subjects for studies on evolution, ecology, taxonomy, ethology and zoogeography. Most specialist believe that they originated in the early Tertiary, but I think that they might date back to the late Cretaceous. The seem to have evolved from something like the recent philodromid genus Titanebo, and certainly they came from that same clade (a genetically closely related group with a relatively recent common ancestor), that includes these and perhaps the sac spiders in the family Anyphaenidae.
There are many references for the arachnids, both on the Internet and in the literature. For those interested in venomous spiders I highly recommend Rick Vetter’s (2015) The Brown Recluse Spider, which includes information on not just that one species, but all known violin spiders, as well as other venomous spiders and those confused with them. There are a lot of books on the subject, but Vetter’s book is by far the best and is well anchored in reality. Other references include Common Spiders of North America by Richard A. Bradley (2012), and Arachnids by Jan Beccaloni and Trudy Brannan (2009). Richard J. Adam’s (2014) Field Guide to the Spiders of California is an excellent local guide.
All photos are by me.