Are Tarantulas Spiders? A Glimpse at Spider Evolution and Phylogeny

Are Tarantulas Spiders?  A Glimpse at Spider Evolution and Phylogeny

Are tarantula’s spiders? Brief reply… sure, they’re certainly spiders. Any of you who comply with me on social media will know that I personal a number of tarantulas, and that is the place this put up comes from. The previous couple of instances that I’ve visited an unique pet store and requested to see their spiders, I’ve been met with the response “we do not actually inventory any spiders, however we do have a number of tarantulas”. Moreover, I’ve seen a few social media posts and YouTube movies from tarantula keepers during which they state that tarantulas aren’t the truth is spiders. This misunderstanding seems to be most outstanding inside the tarantula holding passion, moderately than the science neighborhood. This text was initially going to be a fast correction of this misunderstanding, however have determined to show it into an excuse to jot down about spider evolution and phylogeny. So, if you’re simply right here to seek out out that tarantulas are spiders, then chances are you’ll need to cease right here, however should you’re serious about why that is true and the variations between tarantulas and different spiders, then seize a heat beverage, sit again, and skim on.

Evolutionary Historical past and Phylogeny

Spiders are probably the most specious group of venomous animals on the planet, and arguably probably the most profitable terrestrial predators, apart from maybe predatory beetles (King and Hardy, 2013). At present, there are over 50,000 described species with estimates that the whole quantity could also be nearer to 120,000 species, and data of spider-like creatures that date again 380 million years (Garrison et al., 2016). Attercopus fimbriunguis is a species of prehistoric spider-like creature and is understood from a Devonian-aged fossil. It had many spider options, corresponding to the power to supply silk, however possessed no true spinnerets and possessed a tail-like appendage, not dissimilar to the modern-day whip spiders (Coddington, 1991). While not a spider, it does present how far again the spider ancestry goes, now onto the extant spiders. Spiders (Araneae) are one of many eleven orders of the invertebrate class Arachnida, which additionally consists of the scorpions (Scorpiones), harvestmen (Opiliones), ticks and mites (Acari) and extra (Ubick et al., 2005). Arachnids are Arthropods and sit inside the subphylum Chelicerata.
Residing spiders are divided into two essential teams, the Mygalomorphae and the Araneomorphae each of which possess some key options that make them spiders, together with: spinnerets on the finish of the stomach, eight legs, fangs and two physique segments (Ubick et al., 2005). Tarantulas belong to the group Mygalomorphae, which incorporates a lot of the giant, heavy-bodied spiders which can be sometimes extra primitive than the Araneomorph spiders and have a number of defining options. Mygalomorphs have the primitive Orthognath cheliceral place, which means that their fangs level downwards, like these of snakes. Whereas, the extra derived, Araneomorph spiders have a Labidognath cheliceral place the place their followers transfer aspect to aspect, like a pair of scissors (determine 1.0). Nevertheless, again to the principle level for a second, no matter whether or not they’re a Mygalomorph or Araneomorph, they nonetheless belong to the Arachnid class Araneae and subsequently are spiders. It may generally get complicated with the Araneomorphs usually being known as “True Spiders” however I consider that is merely all the way down to the truth that they make up extra of the species and are extra generally encountered. It does not nonetheless, imply that the Mygalomorphs are “False or Pretend Spiders”.


Determine 1.0 The cheliceral positions of the Mygalomorphs and Araneomorphs. The previous possessing the primitive downwards dealing with fangs (Orthognath) and the latter having the extra superior, sideways transferring fangs (Labidognath).

The cheliceral place is definitely probably the most distinct morphological variations, as with most of the others, corresponding to the massive sizes which can be typical of Mygalomorph spiders aren’t unique. For instance, some Araneomorphs corresponding to Lycosidae (wolf) spiders can attain giant sizes, while the Mygalomorph purse-web spiders (Atypus affinis) and dwarf tarantulas (eg Cyriocosmus sp.) are comparatively small.
There may be really a 3rd group of spiders, the Mesothelae, that are the oldest and most primitive group, with just one dwelling household (Liphistiidae) consisting of roughly 100 species, which share the primitive Orthognath cheliceral place. Mesothelae are restricted to China, Japan, southeast Asia, and Sumatra (Coddington, 1991). They’re probably the most primitive of the teams and possess larger belly segmentation and fewer developed spinnerets (Coddington, 1991). The phylogeny of those teams and their traits may be seen in determine 2.0.

spider phylogeny (2)

Determine 2.0 The phylogeny of the three spider teams with the Taxa in common font and characters in italics. Not all of the Araneomorph teams are represented, the three proven symbolize the group and present among the characters which can be shared with the Mygalomorphae (corresponding to the scale of Lycosids). Taken from Ubic et al., 2005.

Habits and Pure Historical past

Together with the differing morphological traits, the Mygalomorphs and Araneomorph spiders additionally differ of their life. While each teams are extremely numerous in behaviours, there are a number of traits that work as a normal rule of thumb in terms of separating them. For instance, how they use silk. The evolution of silk manufacturing is undoubtedly one of many essential developments that has led to the success of the spiders (Blackledge et al., 2009). While the precise timeline continues to be not clear, it’s estimated that the Araneomorphs diverged from the Mygalomorphs roughly 240 million years in the past (Garb et al., 2007). This divergence and the sudden radiation of Araneomorphs may be, to at the least some extent, attributed to their developments in silk manufacturing and use (Garb et al., 2007). The Mygalomorphs are extra primitive of their silk use than the Araneomorphs, utilizing it primarily to assemble burrows, hides and trapdoors. These spiders use silk in its extra primary kind, some utilizing it primarily for housing building and only a few for prey seize (such because the purse-web spider – Atypus affinis). Whereas, the Araneomorph spiders have advanced the power to seize their prey utilizing webs, spiders are so numerous that there’s a big selection in simply the webs of the Araneomorphs, which in some instances can be utilized as an figuring out function… they’re that distinct.

While some, such because the net-casting spiders (Deinopids) utilizing the primitive, non-sticky (cribellate) silk that catches prey by way of Van der Waal pressure interactions and bodily entanglement (Piorkowski and Blackledge, 2017). The Araneoidea spiders make the most of a extra superior type of silk, often known as viscid silk, which makes use of an aqueous glue-like substance that coats the silk core (Piorkowski and Blackledge, 2017). The evolution of the viscid silk is regarded as one of many greatest contributing elements of the success and variety of the Araneoidea spiders. I might simply go into masses extra element, waffling on about why that is the case, however we’re already beginning to strategy 1,000 phrases, so I will save that for an additional time. Silk manufacturing and use is simply one of many multitude of things which have contributed to the success of spiders and there are a lot of extra variations between the teams. I think about I’ll deal with extra of those in particular person posts sooner or later.

Again to the comparability of Araneomorphs and Mygalomorphs. While the spinning of orb webs is unique to the Araneomorphs, as is the viscid silk, most of the characters aren’t unique. For instance, the Lycosids and Salticids are simply two examples of Araneomorphs that don’t use silk in any respect for prey seize, however as a substitute hunt actively, extra akin to the Mygalomorphs. Demonstrating that there’s a lot of cross over between the 2 teams, with the Mygalomorphs being the ancestral situation, they’re base of spider evolution. The Araneomorphs have simply managed to innovate these base options, such because the manufacturing of silk and go down a myriad of various roots. Utilizing silk in a plethora of unimaginable methods has result in spiders being remarkably profitable and while many Araneomorphs use extra complicated methods, the constructing of silken homes and journey traces, mixed with sheer brutality and measurement, has enabled the Mygalomorphs to outlive millennia.


I really feel as if I could have gone off monitor slightly bit, however it’s straightforward to do when spiders possess a cornucopia of fascinating traits and behaviours. Anyway, the purpose is that, whatever the big variety amongst all spiders, and the variations between the Mygalomorphs and Araneomorphs, all Mygalomorph spiders (together with tarantulas) nonetheless belong to the Arachnid class Araneae and subsequently are certainly spiders. I hope you’ve got loved this considerably all over put up about spider teams and their variations, with the underlying goal of displacing a typical misunderstanding. It’s extremely possible that I’ll do future posts going into extra element on the totally different silks utilized by spiders in addition to spider evolution, just because (in case you hadn’t guessed), I discover it fascinating. Hopefully you do as nicely.

Thanks for studying, till subsequent time.

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And be at liberty to seek out me on Instagram for pics and movies of my tarantulas, normal wildlife images and simply my life. Matthew Woodard (woodard 303).

My little Trinidad Dwarf Star Tarantula (Cyriocosmus elegans), proving that not all tarantulas are big.


Blackledge, TA, Scharff, N., Coddington, JA, Szüts, Wenzel, JW, Hayashi, CY and Agnarsson, I. (2009). Reconstructing internet evolution and spider diversification within the molecular period. PNAS, 106(13), 5229-34.

Coddington, J.A. (1991). Systematics and evolution of spiders (Araneae). Annual Assessment of Ecology and Systematics, 22565-92.

King, GF and Hardy, MC (2013). Spider-venom peptides: Construction, pharmacology and potential for management of insect pests. Annual Assessment of Entomology, 58, 475-96.

Piorkowski, D. and Blackledge, TA (2017). Punctuated evolution of viscid silk in spider orb webs supported by mechanical habits of moist cribellate silk. Naturwissenschaften, 104(67).

Ubick, D., P. Paquin, PE Cushing, and V. Roth (eds). 2005. Spiders of North America: an identification handbook. American Arachnological Society. 377 pages.