You probably do have little “ghosts” (as in ghost spiders, of course) in your garden. They are spiders of the family Anyphaenidae and are so named because they not only are active at night, but some of them—such as this one—have a decidedly pale and mostly translucent, ghost-like* 👇 appearance:
Despite that catchy moniker, though, most ghost spiders, such as the one below, do not share the wan look of Wulfila, looking much more like…well…plain old, everyday, small** 👇 spiders.
Ghost spiders do not make capture webs, and use their silk only for drag lines, egg sacs, and to make resting/hiding places—often in curled leaves.
To catch prey, they rely on speed: They are fast*** 👇 runners that are known to dash about constantly when hunting. In fact, they often seem to be on little sugar “highs,” training hard to develop their lightning-fast moves by overdosing on the sugars to be found in plant nectars (Taylor and Foster, 1996).
I kept two juveniles alive after their capture last summer, waiting for them to mature so that I could photograph and identify them. On two occasions I opened a jar ever so cautiously to check on its resident after having carefully ascertained that it was not near the opening: Twice there was no spider to be found in the open jar, despite my having seen it moments before in the unopened jar!
In one case it had simply vanished-—as befits a specter—never to be seen again. In the second case, although I did not see it making its escape, I spotted it seconds later hightailing it off the back of my desk, leaving a tiny cloud of dust lingering in the air as I heard the faintest of “meep, meep!” sounds.
And so, I shall try again! At this writing, I have another species of ghost spider in the same type of jar. I collected it as a subadult male a week ago, and yesterday it had molted, meaning it’s now a mature, hence identifiable, male. I already knew it to be a ghost spider, and probably Hibana gracilis (Hentz, 1847) at that**** 👇 but, barring yet another escape, I’ll now be able to confirm it.
One of the things I’ve noticed about spiders, is that people invariably exaggerate their size…sorta like…well…some other things* 👇.
Clearly, it’s human nature to exaggerate the good things in life. Sadly, though, most of the spider stories I hear being embellished are not presented as being Good Things™. Instead, the goal seems to be to enhance some unspoken degree of terror by enlarging the size of the threat.
So how big are spiders? Well, first off, when we “officially” measure spiders, it’s from the front of the cephalothorax (that’s the front end, exclusive of chelicerae or pedipalps) to the tip of the abdomen (excluding any spinnerets which may protrude).
Notice that legs don’t count!
However, when speaking of The Largest Thing, we not only exaggerate, but, when spiders are the subject, people usually include the legs, presumably for effect. Thus, the largest spiders known are Theraphosa blondi (Latreille, 1804) which can measure 13cm (5.1in), but to make that even more impressive, add the legs , and it becomes 30cm (ca. 1 foot)–although if that’s what you’re counting, it ceases to be the world’s largest spider** 👇.
Of course, most spiders are small. In fact, about half of the known North American spider species*** 👇 are very small: less than 3mm long (about the thickness of three credit cards) at maturity.
Males of the smallest species known, Patu digua Forster & Platnick, 1977**** 👇, measure 0.37mm (about the diameter of a 0.015in guitar string, for my musician friends). In a classic bit of understatement, the species’ authors wrote of P. digua: “[their being] the world’s smallest known spider[s] makes working with them difficult; many characters…are difficult or impossible to resolve…and can be seen in detail only with [a] scanning electron microscope.”
Just think: It would take ca. 810 P. dagua lined up***** 👇end-to-end (no legs) to reach from one end of T. blondi’s legs to the other.
With no exaggeration!
*👆 Fish. Yeah, that’s what I was thinking of! Fish.
**👆 If we’re counting legspan, the largest known spider is a huntsman found in Laos: Heteropoda maxima Jäger, 2001, the legspan of which can exceed a foot.
***👆 N.B. the number of individuals in those small species vastly exceeds the numbers of individuals in the larger species.
****👆Patu digua is in the family Symphytognathidae–they’re all small. In fact, Lehtinen (1975) wrote: “the Symphytognathidae… is surely a polyphyletic dump heap of minute Araneoidea.”
*****👆 I said “lined up” rather than “standing,” because we’re not counting legs, so how could they be standing?
Bradley, Richard A. 2013. In Common Spiders of North America. (1st Edition. University of California Press; Berkley & Los Angeles, California, USA) p.4.
Forster, R. R. & Platnick, N. I. 1977. A review of the spider family Symphytognathidae (Arachnida, Araneae). American Museum Novitates 2619: 1-29.
Lehtinen, Pekka T. 1975. Notes on the phylogenetic classification of Araneae. Proc. Sixth Internatl. Arachnol. Congr., pp. 26-29, figs. 1-24.
You are probably familiar with “gauchos,” the outstanding South American horsemen who used bolas to catch running livestock and/or to capture small animals and birds to eat.
The idea is that the rocks or other weights on the ends of joined lines spread out when the twirling bolas are thrown; when one of the lines strikes an animal or its leg, all the spinning weights will quickly wrap around the target, thus felling livestock…and subduing or killing small game.
Now, bolas spiders are morphologically and genetically members of the family Araneidae, which spiders are called “orb weavers” because they usually make those stereotypical orb webs so well known to all. (See this 2016 post for some of my prolix ramblings about orb webs.) Bolas araneid spiders, though, make no capture webs, being instead nocturnal hunters: They are, therefore, easily overlooked as they tend to remain motionless during the day, trying very hard to look like bird droppings or buds on twigs.
While these non-orb-weaving orb weavers make no web, they do use sticky silk to ensnare prey, and, as you no doubt have sussed out, they do this in a manner reminiscent of the gauchos’ bolas.
While the technique varies somewhat among the more than 50 species of bolas spiders, a general description of what a bolas spider does is to make a single strand of silk having a large glob of stickum (more, in some species) on its end. The spider dangles this sole line from its perch and waits for a flying insect to appear, and then swings its sticky bola at it, or–depending on the species–it may swing the bola constantly, increasing the chances of its randomly making contact with a suitable supper.
Once a hapless insect is stuck to the line’s end, it is hauled up to be dispatched and eaten in normal spider fashion.
Cool, eh? But the very best part is that these spiders stack the deck in their favor…bolas spider species have evolved the ability to produce pheromone mimics that male moths of particular species detect and respond to as their species’s sex pheromones! Yep, those testosterone-poisoned males follow the pheromone trail right to the spider’s bola.
And, should the spider miss its attempt to snag it, the by now frantically eager male will hang around, still lusting for the consensual “fang fatale” that lured him in, giving our spider protagonist multiple opportunities to catch its meal.
A few months back, I was “vetting” some photographs that had been submitted to the North Carolina Biodiversity Project’s Arachnid page when I came across this photo, submitted as possibly being Agelenopsis pennsylvanica (C. L. Koch, 1843), one of the grass spiders (sometimes called “funnel weavers”) of the family Agelenidae.
A Grass Spider
Now, right off, it didn’t look to be Agelenopsis to me, for a number of reasons, none of which are easy to specify–it just didn’t look right.
When all one has is a photo, though, identifications can get tricky, and–my not being from ’round these parts–I didn’t recognize what seemed to me to be what should be a readily identified species.
I am generally hesitant to start searching online photo collections looking and hoping for a match: After all, not only do many spiders look similar, but online photos can be misidentified. So, I did the next logical thing: I asked a highly experienced person also working on the project if he had any thoughts.
He immediately responded with a likely ID of Barronopsis texana (Gertsch, 1934), another agelenid genus known from NC…and he was spot on, of course.
As B. texana was a species which I’d never seen (or even heard of) before, I naturally did some literature searching to learn something about it. First off, I learned why I was unfamiliar with it: It occurs from NC south through Florida, thence west into Texas: All my collecting has been in the Midwest and Northeast, so I’d simply never come across Barronopsis before.
So, armed with this knowledge, I was ready for my next encounter, right? Um…no, this is where the “fool me twice” bit kicks in, I’m embarrassed to admit.
A couple of months later, a neighbor brought a living spider to me, about which I immediately proclaimed (in my very best know-it-all-tones) “that’s an immature wolf spider!” and then–using the Occam’s Razor Theory of Spider Identification–promptly guessed at a species.
OK, I’m sure you see where this is going! When I got it under the microscope it was immediately clear that this was not a lycosid (wolf) spider at all, much less the species I had guessed. Nope, wrong family altogether, its being (as you’ve no doubt already surmised) another of the agelenid Barronopsis texana, of which I had so recently been totally ignorant–and, sadly, had apparently remained.
But, my suffering this ignominy did, at least, lead to a happy ending. A few weeks later, I was visiting a relative’s house some miles away when I found a spider molt skin having familiar markings. I looked around and found funnel webs on a building wall, from which webs I captured an adult female and an adult male B. texana. And this time I got it right!
Morals of the story:
No matter how much I think I know, there is always someone who knows a lot more.
Don’t hesitate to say “I’m not sure–let me get a closer look”.
Chances are pretty darned good that the answer to the title’s question is “No.”
After all, the Cambridge Dictionary says a poison is “a substance that can make people or animals ill or kill them if they eat or drink it” [emphasis added], while the Oxford Dictionary is a bit more explicit: “a substance that causes death or harm if it gets into the body” [emphasis added].
What may be poisonous, though, is venom (rattlesnake or otherwise) which, according to the Oxford Dictionary is “the poisonous liquid that some snakes, spiders, etc. produce when they bite or sting you.”
So, basically, a rattlesnake is not a poison; in fact, “rattlesnake” can be found on exotic meat menus, and, barring any open wounds in or around your mouth, you can drink rattlesnake venom without ill effect. Or so I’ve read. This definitely falls into the “DO NOT TRY THIS AT HOME!” and “I AM SPECIFICALLYNOT RECOMMENDING THIS!” categories.
Thus, while the snakes shown below are not poisonous, they are highly venomous!
OTOH, the venom shown being collected in the next photo is most assuredly poisonous when injected into most mammals!
So what does this mean for spiders and some stinging insects? Well, first off, it means that most simply aren’t poisonous. Insofar as I know, you can eat any spider whatsoever without fear of poisoning. (And here, I must repeat my “I AM SPECIFICALLYNOT RECOMMENDING THIS!” caveat.)
“Venomous,” though is a different matter.
As of this writing, there are 48,974 recognized species of spiders in 128 families* 👇. Among these, only one family, the Uloboridae–comprising only 287 species (0.6%of that almost 49K)–does not produce venom. All the rest do, and it’s safe to assume that probably more than that remaining 99.4% of all the spiders you’ve ever noticed do produce venom.
Why produce a toxin at all? Well, it serves spiders the same way that venom serves dangerous snakes: It is used mostly to subdue prey, though it may be used for defense when necessary.
Thus, when people ask me “Is this spider `poisonous?'” I have to point out that almost all spiders are venomous, but more importantly, almost none dangerously so (and none poisonous).
In fact, only a tiny handful of the 48,687 venomous species known are known to be capable of causing serious issues in humans** 👇! Furthermore, many (most?) spiders are just so small that they cannot deliver venom to humans, their fangs being unable to penetrate human skin.
In fact, while I have no idea what spider has the smallest fangs in proportion to its body, I do know that Scytodes atlacoya, the spitting spider I find so interesting, has a carapace (the head-thorax part) generally ca. 3-4mm (ca. 3 pennies thickness) wide: Their fangs are only ca. 0.1mm long, or about the thickness of 2 sheets of paper–not much of a threat!
On the other hand, the dysderid spider below illustrates sort of the opposite ratio: you can really see the fangs on this beauty! This common species lives in leaf litter and duff, where they feed on woodlice, the critters sometimes called “sowbugs” or “pillbugs.” It uses those disproportionately large fangs to penetrate their armored plates. (But fear not: They’re only ca. a centimeter long, and not aggressive.)
So the long and short (ha!) of it is: Most critters aren’t poisonous (some are, though–e.g. several species of puffer fish are deadly poisonous to eat!). OTOH, almost all spiders are venomous, but it’s unlikely that one would bite you anyway. Furthermore, if you do somehow provoke a spider into biting you, it’s extremely unlikely to be one of those few species whose venom can actually cause a problem in humans. So, honestly: Don’t sweat it–far more Americans are killed by horses every year than by spiders!
*👆 Per the authoritative World Spider Catalog **👆 Of course, as with any bites or stings, some individuals may have allergic reactions to the proteins in spider venom.
So…last time, I spoke of weird scientific names, and told you that this time I would address common names.
E.g., I live in North Carolina, where the spider figured below is often called a “writing spider*”👇. However, it’s also called the “yellow garden spider,” “black-and-yellow argiope,” “black and yellow garden spider,” “yellow garden orbweaver,” “black & yellow argiope,” “banded garden spider**👇,” “zipper spider,” “McKinley spider” and–in California, I’m told–the “golden orbweaver”:
Now, by common names, I mean those colloquial names we all use in our native tongues for organisms of all stripes. However, even in the same language, a particular species may have several different common monikers, often varying by geographic region.
Well, then, what should we call it? I call it “Argiope aurantia,” and I suspect (and hope) that my family knows what I’m talking about…but my neighbors sure don’t.
So what is to be done? The simplest and most accurate solution is to avoid colloquial names altogether, and use only the scientific name: After all, that’s preciously why they exist, and it is no coïncidence that they’re the exact same in all languages and all countries.
Alas, that’s not going to happen.
But at least for scientific publication, the scientific name is mandatory. Except, after once identifying a well known species by its scientific name, an author can use a common name approved by the publishing organization. In this way, I could write about the “yellow garden spider, Argiope aurantia Lucas, 1833,” and from that point on merely call it the yellow garden spider.
In order for this to be consistent, though, the organization must maintain a list of “approved common names.” You may have guessed from my usage that among all those common names for Argiope aurantia, the only one acceptable in a scientific publication of the American Arachnological Society–and therefore the only one I would use in casual conversation–is “yellow garden spider.”
At this writing, that spider list recognizes common names for only 220 spiders (of almost 49,000 described species), 131 mites, 48 scorpions, 3 harvestmen, 2 pseudoscorpions, and 1 vinegaroon.
The Entomological Society of America maintains its own list, 61 pages long (that’s about 2,400 species, but I’m not going to count them) of (mostly) insect common names approved for its publications (out of ca. 1 million described species).
These organizations take the recognition of common names quite seriously and have strict rules, not only for their acceptance, but for their syntax: E.g. “orbweaver” is one word (hyphens are eschewed), “leaffooted bug” takes no hyphen between the Fs, but “bug” is a separate word, as it is a “true bug”; a “sowbug” is not a bug (much less an insect) so it’s one word.
Furthermore, common names take no upper case, unless as the first word of a sentence or a proper noun: e.g. “American cockroach,” “Gertsch antmimic,” “McDaniel spider mite.”
This all matters. Well, maybe not to normal Homo sapiens, but to those of us nerds who really are concerned with knowing as closely as possible how any given critter is classified. Let’s face it: When telling your neighbor what’s climbing up his back, a “big ol’ red & black slimey, bitey-lookin’ thing” will still suffice.
*👆 The yellow garden spider (see what I did there?) is presumably called the “writing spider” ’round these parts because they spin a stabilimentum: i.e. a zigzag thickening of silk in the center of their their web, whereupon they rest. Local legend has it that if the spider writes your name in that zigzag, you’ll die that very night! **👆 Unfortunately, banded garden spider is the accepted common name for a different species, viz. A. trifasciata (Forsskål,1775). This source of confusion highlights one of the problems with “unofficial” common names!
Last time we discussed the process of naming biological organisms following Carl Linnaeus’s binomial nomenclatural system, i.e. each named critter has two parts to its name, a genus and a specific epithet. These names, by international agreement use Latin or Greek endings, so as an example of an odd species name, I mentioned “Cartwrightia cartwrighti Cartwright, 1967,” where: 1) the genus, Cartwrightia was created in 1958 to honor Oscar Cartwright who, in 1967, 2) named a new species in in that genus, cartwrighti, to honor of his brother, Raymond, and, since the Oscar named the species, 3) his name as author follows the species name, so we get yet another “Cartwright.”
Now, I confess that for most of my entomological career, I was a die-hard, stick-in-the-mud traditionalist who believed and espoused the notion that scientific names should be descriptive, e.g. Homo sapiens Linnaeus 1758. or Latrodectus mactans (Fabricius, 1775). The etymology of the former was discussed in my previous posting; the latter is interesting because the Greek Latrodectus can mean “secretly biting” and the Latin mactans can mean “slaughtering or killing.”
Oh, yeah–lest I forget–L. mactans is the spider commonly called a black widow.
I grudgingly accepted naming species for scientists, such as Messrs. Cartwright, above, and even places; e.g. the defunct cockroach pictured above is in the genus Periplaneta, the Greek roots of which can mean “all around wanderer.” The species is P. americana: not too hard to figure that one out.
But I drew the line at non-scientists or even–perish the thought–fictional characters. Until, that is, my favorite cartoonist of all time was honored by having a chewing louse*👇, Strigiphilus**👇 garylarsoni Clayton, 1990 so-named in recognition of Larson’s “…enormous contribution…made to biology through [his] cartoons.”
And then I saw this spider:
This, friends, is Eriovixia gryffindori Ahmed, Khalap & Sumukha, 2016. It’s commonly called the “Sorting Hat spider.” Definitely fictitious, right? But what a perfect name!
BTW, it could be a bit difficult to see this spider on dry leaves:
So not only have I come to accept fanciful names, I now embrace them. They stir my curiosity, and have led to many delightful hours of researching names and animals to which I would otherwise have paid no attention!
In closing, I give you the longest proposed scientific name, a fungus eponymously named for the famed town***👇 in Wales, Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch: Myxococcus llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogochensis Chambers et al., 2020 (the “ensis” on the end indicating that it is named for that town).
Next time–the dread “common name”!
*👆 Chewing lice are commonly called “bird lice,” and this species is only found on owls. **👆 Strigiphilus can be loosely translated as “bristle-lover.” ***👆Google Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch (without the “ensis”).
Back in June of this year, I wrote about the human propensity for categorizing and naming things: All things–people, animals, tools, geographic entities, diseases, cars–you (*ahem*) name it!
As a biologist, though, my concern here is the naming of organisms, and owing to my own leanings, I shall generally focus on animal names in what is intended to be a series of posts.
Almost 300 years ago the Swedish naturalist Carl Linnaeus proposed a binomial (“two-name”) system for naming organisms (initially plants), which system has been globally accepted and adopted. Simply put, the name given to each species of living or extinct organism comprises two parts: a genus and a specific epithet. The former is always capitalized; the latter, never, even when it’s a proper noun, as we shall see.
Thus, any organism reading this is a member of–in all likelihood–the genus Homo…and in particular is a member of the species Homo sapiens.
Of course, people being people, we made rules about such names–first and foremost being that all such names shall be either of Latin or Greek origin…or at the very least “Greek- or Latinized,” i.e. having Latin or Greek endings. By international agreement only the Roman alphabet is used. Furthermore, everything being appropriately “-ized,” the names of all species are therefore treated as foreign terms and set in italics accordingly.
So, the name of our own species comes from directly from the Latin words “Homo” for “man,” and “sapiens” (its being the present participle of the Latin verb sapere, translated as “to be wise”), and neither term required any Latinization.
Naturally, though, many things have been named in a manner that takes liberties with the “-ized” rule, so e.g. we have the dung beetle genus “Cartwrightia” erected by Federico Islas Salas*👇 to honor one Oscar Cartwright (note the “-ia” Latinizing his surname); Old Oscar himself later named a new species of Cartwrightia for his brother, Raymond, so we have the species Cartwrightia cartwrighti (the “-i” simultaneously Latinizing the name and indicating that it’s named in honor of someone, in this case that someone having the same surname, of course).
Making this name more fun (Ha! As if that were even possible!) is that for scientific publication the name of the original author of a species and the year of its description are listed after the binomial, so I should have written “Homo sapiens Linnaeus, 1758,” and, for our dung beetle we get (you ready?):
Cartwrightia cartwrighti Cartwright 1967.
So, there’s the basic structure of scientific names. Next time, we’ll discuss a few other organisms that have been given um… “unusual” names!
*👆 Islas erected the genus Cartwrightia in 1958, and he named its first–and therefore defining–species “Cartwrightia intertribalis Islas, 1958).”
I had threatened a few posts back to add some more spider-themed music, and have decided that the time has come.
In specific, when I first became seriously interested in Scytodes atlacoya, I had gone to the World Spider Catalog (WSC) to see just how many species of Scytodes might be involved, and was rather surprised to find that there were 222 (up to 224 at this writing)!
Coïncidentally, a few months later I stumbled upon a Hank Snow video of a song called I’ve Been Everywhere, Man, written in 1959 by an Australian named Geoff Mack, and based on the names of some Australian towns. Mack later wrote an American-town version, subsequently recorded by Hank Snow in 1962 and covered by a number of artists, Johnny Cash and Willie Nelson among them.
Owing to the number of species found in the genus Scytodes, I figured I’d try to do something based on Geoff Mack’s song, using the WSC list. So, following the original song’s format, I was able to squeeze almost 100 of the specific epithets into this version.
To make it easier for you to sing along, I have subtitled the lyrics for each of the four verses, but to see them, be sure to turn on the “Closed Caption” feature of YouTube. On a cell phone, do this:
On a desktop:
So, herewith, my version of Scytodes Everywhere, Man
If you get a chance, check out the version Hank Snow recorded: He’s really honking along! In fairness to me, though, please note that he modulates to a different key after each chorus, thus buying him extra two measures in which to inhale!
Back on 01 August 2020, I wrote about finding a species of spitting spider,Scytodes atlacoya, in my home in central North Carolina, which species had not hitherto been recorded from this state. It occurs to me that I offhandedly mentioned that spitting spiders were appropriately named, but failed to elaborate.
The moniker “spitting spider” can be applied to any of the 245 species*👇 of spiders in the family Scytodidae, and it relates to their method of prey capture.
With the exception of a single family, **👇 all spiders have venom glands. The scytodids, though, have highly modified glands that produce not only venom but silk and what can best be described as “glue,” although I am prone to using the technical term: “stickum.”
Most spiders’ venom glands are in the cephalothorax***👇 and connect to the base of each chelicera; the venom is then released through small holes in the pointy, business ends of the cheliceral fangs. In the evolution of their multipurpose venom glands, those of spitting spiders have become quite enlarged and take up a lot of space, giving the spiders a rather pronounced and distinctive humpedheadedness.
Scytodids have rather poor eyesight, so they use their super-long front legs as distant early warning devices, and as hunting range-finders. When they assess something in range to be potential prey, they spit their glue/silk/venom mix onto it through the holes in what are remarkably small fangs.
In doing this, they emit a stream of solidifying silk covered with stickum and venom. As they expel this mixture, the fangs oscillate rapidly, creating a zigzag pattern. As there are two fangs doing this simultaneously, the glop not only zigzags, but crisscrosses!
The silk not only solidifies almost instantly in air, it quickly contracts, which, owing to its gluey component, binds the intended prey and can also serve to stick it to the substrate.
After the prey has been rendered pretty much immobile, our spider approaches carefully and often loosely wraps it in more silk from its spinnerets. Eventually, using those tiny fangs, it nips through a thin spot in its prey’s “skin,” and injects its fast-acting venom to kill–or at least paralyze–it.
Then, the spider begins an interesting process of alternately forcing digestive juices through the fang-made-holes into the prey, and sucking out its liquefied contents through those same holes (spiders can’t suck anything through their fangs!).
To entertain you, here’s a silent, (don’t turn up those speakers!), real time, 35 sec. video I recorded showing a young S. atlacoya having captured, and now eating, an also young cobweb spider (you’re looking at the underside of the atlacoya‘s cephalothorax on the left):
At ca. 3 seconds in, you’ll see some dark material being sucked into our atlacoya though the holes made by its fangs–watch the moving black spot on the prey: Our atlacoya is using the prey’s leg as a straw!
Around 10sec in you can see the prey collapsing as its contents are being sucked out.
At about 20sec you’ll see that atlacoya stops sucking, and instead forces more digestive juices into the prey, refilling the latter’s abdomen as if it were a water balloon!
And finally, at ca. 25sec, you’ll see more specks of matter being sucked in through the leg-turned-straw.
And, just in case you’re wondering, the alternate sucking/refilling in that video occurred over 20 times during the more than half hour it took before atlacoya had sucked its victim dry.
*👆 i.e., 245 species of Scytodidae accepted by the World Spider Catalog at this writing, 03 Sep 2020.
**👆 The spider family Uloboridae, hackled orbweavers, is the only known spider group having no venom. They bore their prey to death with bad jokes.
***👆 Spiders have two distinct body segments. Their front end is a combination of a head and a thorax–i.e. cephalothorax, where cephalo=head, thorax=”chest.” The other segment is the abdomen. Insects, you’ll recall, have three such segments, the head and thorax being separate.