Identifying common orbweavers from the underside - Wiki

This is an experiment with a tutorial that can be edited by anyone. It’s also intended to be the kind of thing discussed here. Sometime in the future, iNaturalist will have a place for content like this on taxon pages. When that time comes, I will transfer all the content in this tutorial over to iNaturalist, so you needn’t fear losing any work you put into this.

Most often spiders are photographed from above, but observations of orbweavers often only have a photo of the underside of a spider on its web. This is a tutorial about how to identify common orbweavers from the underside.

BugGuide has a page with ventral images of some orbweavers which covers more species from North America, but in less detail.

Table of Contents

Basic Vocabulary

I try to use plain language here and avoid technical terms as much as possible, but it’s still much easier to describe the underside of a spider in text if one is allowed to use a handful of topic-specific words:

spider body-plan vocabulary
Photo © Mark Nofsinger

The photos featured here are from iNaturalist observations which show both the top-side and the bottom-side of the same spider, and which the observer has licensed for non-commercial uses.

So far, all the photos here are of female orb-weavers. Males often have significantly smaller abdomens relative to their heads, are significantly smaller overall compared to females, and often don’t build orb webs, though they often hang out on or near an orb-web a female has built. If photos of the undersides of males turn up often enough, someone should add a photo of a male to the section for the species.

Family Araneidae (Orbweavers)

Almost all orb-weaving spiders are in this family. However, a few are in other families such as Tetragnathidae, Uloboridae, and Phonognathidae, so if all you have is an orb web then the narrowest ID that contains them all is superfamily Araneoidea.

Genus Argiope (Garden Orbweavers)

5 species in North America, 89 worldwide. Large and colourful enough to attract attention, thus very commonly observed. Spiders in this genus often have a zig-zag or X-shaped decoration on their web.

Argiope aurantia (Yellow Garden Spider)


Photo © Erin Faulkner

A North and Central American species. In Canada and all but the southernmost parts of the US it can only be confused with A. trifasciata. Legs usually solid black at tips, solid brown near body (compare with banded A. trifasciata), but early in the summer sometimes have banded legs. Underside of abdomen difficult to distinguish from A. trifasciata, but epigyne may be distinguishable? Sternum has a single solid yellow stripe, with no distinct lobes or separate yellow marks.

Argiope trifasciata (Banded Garden Spider)


Photo © aarongunnar

A global species. Legs always banded, never bicolored like A. aurantia. Underside of abdomen difficult to distinguish from A. aurantia, but epigyne may be distinguishable? Sternum has a large central yellow stripe like A. aurantia, and sometimes distinct lobes or separate yellow marks in pairs on either side of the central stripe, unlike A. aurantia.

For A. aurantia vs. A. trifasciata, those with unbanded legs are definitely A. aurantia, and those with side-lobes or dots on the sternum are definitely A. trifasciata. The difficult ones are those with both banded legs and a stripe on the sternum with no side-lobes or dots. It can be worth the effort to get a picture of Argiope sp. from another angle, since the top and sides of the abdomen are instantly identifiable.

For juveniles, see this comment.

Genus Araneus ( Angulate and Roundshouldered Orbweavers)

Historically the “miscellaneous” genus of the family. 50+ species in North America, 576 species worldwide.

Araneus diadematus (Cross Orbweaver)


Photo © Joe Bartok

Among the most commonly observed orbweavers in the world. Introduced to North America from Europe. White marks bracketing underside of abdomen. Marks straighter, more angular than Larinioides. Black inside the overhang of the bracket marks, dark brown between. In poor light the dark brown may be indistinguishable from the black. Sternum dark, unlike Neoscona. Female epigyne has a little hook which extends slightly out over the abdomen, which can be useful to confirm ID.

Araneus marmoreus (Marbled Orbweaver)


Photo © peggyo

A northern-hemisphere species. Yellow marks bracketing underside of abdomen. Legs orange closer to body. Huge color variations in this species; some are all black-and-white instead of yellow, orange, and black, which can make identification difficult.

Araneus trifolium (Shamrock Orbweaver)


Photo © LJ Moore-McClelland

A North American species. Adults have a dark reddish underside with no bracketing marks. (Juveniles different?)

Araneus bicentenarius (Giant Lichen Orbweaver)


Photo © Celeste Ray

An eastern North American species. Has a uniquely-shaped mark in the middle of the abdomen which looks like a T with a wide triangluar base and bulbous arms, reminiscent of a rotary-dial telephone. Dark sternum overlaid by a pale central stripe with one pair of branches angled toward the abdomen. Some species of Eustala can be mistaken for A. bicentenarius and vice versa. A. bicentenarius are much larger than Eustala, but sometimes there is nothing in a photo to indicate the size of the spider. Example.

Araneus gemmoides (Cat-faced Orbweaver)


Photo © Kayleyana Anderson

A western North American species. Pale marks bracketing underside of abdomen, similar to Araneus diadematus but shorter. Sternum dark with a pale center, unlike A. diadematus.

Araneus nordmanni (Nordmann’s Orbweaver)


Photo © Nick Block

A northern-hemisphere species. Underside of abdomen has two white dots on a black background. In exceptionally good photos, faint lines connecting the dots to the sides of the abdomen are visible, as above. Juvenile A. nordmanni, which are tiny yet build webs like adults, are more likely to have the dots fully touching the sides of the black area, forming the bracket-like markings common on other Araneus. A few examples from Alaska also look more like standard Araneus.

Araneus cavaticus (Barn Orbweaver)


Photo © Kyle Jones

The species featured in the children’s book Charlotte’s Web. Only found in and around the Appalachian Mountains of eastern North America. Particularly abundant in Vermont and New Hampshire. Males and females often observed together under the eaves of barns and other buildings. Brackets on underside of abdomen similar to A. diadematus, sometimes but not always completely black between them, otherwise brown in the centre and black underneath the brackets. Sternum black. Legs noticeably longer than A. diadematus, with dark bands around the centre of each leg segment as well as at the joints, unlike other Araneus. Banding on the legs is often fainter than in the photo above. Males have even longer legs than the females.

Genus Neoscona (Spotted Orbweavers)

8 species in the US and Canada, 126 worldwide.

Neoscona crucifera (Spotted Orbweaver)


Photo © Even Dankowicz

An eastern North American species. White marks bracketing underside of abdomen often resemble the bottom half of square brackets, with a well-defined, angular corner. Upper half of brackets usually connected to the lower half unlike N. oaxacensis, and the part nearer to the head is usually about the same brightness as the part further away, unlike N. arabesca. Sternum pale surrounded by dark, unlike entirely dark Araneus and Larinioides.

Neoscona oaxacensis (Western Spotted Orbweaver)


Photo © Tony Iwane

Found in the west coast and southwestern states of the U.S. south to South America. White marks bracketing underside of abdomen similar to N. crucifera, but much more often detached from each other. Sternum pale surrounded by dark, unlike entirely dark Araneus and Neoscona. Coloring highly variable, ranging from the very dark body and banded legs in the photo above to very pale.

Neoscona arabesca (Arabesque Orbweaver)


Photo © Julie Filiberti

A North and Central American species. Pair of white marks on either side of underside of abdomen. Dim white marks on underside of abdomen towards head, unlike N. crucifera. Sternum pale surrounded by dark, unlike Araneus and Larinioides.

Neoscona domiciliorum (Red-femured Spotted Orbweaver)


Photo © Joe Walewski

Found in the south-eastern US. Femurs (the parts of the legs nearest the body) are bright red (though it should be noted that other Neoscona can also have similarly red femurs). White marks bracketing underside of abdomen similar to N. crucifera, but much more often detached from each other. Sternum pale surrounded by dark, unlike entirely dark Araneus and Neoscona.

Genus Larinioides

3 species in North America, 7 world-wide.

Larinioides cornutus (Furrow Orbweaver)


Photo © Dan Toth

A northern-hemisphere species. White marks bracketing the underside of the abdomen are more curved than on Araneus. Underside of abdomen black throughout, unlike Araneus diadematus. Sternum dark, unlike Neoscona. Lacks dark band on middle of second-to-last segment of rear legs, unlike L. sclopetarius and L. patagiatus.

Larinioides sclopetarius (Grey Cross Spider)


Photo © Jeremy Hussell

A northern-hemisphere species. White marks bracketing the underside of the abdomen are more curved than on Araneus. Underside of abdomen black throughout, unlike Araneus diadematus. Sternum dark, unlike Neoscona. Dark band on middle of second-to-last segment of the rear legs, unlike L. cornutus. Difficult to distinguish from L. patagiatus by the underside alone. However, Grey Cross Spiders are much more common on buildings than the other species. E.g., they’ve been photographed on webs on the outside of windows 50+ stories above ground on skyscrapers in Chicago.

Larinioides patagiatus (Ornamental Orbweaver)


Photo © Анатолий Озерной / Anatoliy Ozernoy

A northern-hemisphere species. White marks bracketing the underside of the abdomen are more curved than on Araneus. Underside of abdomen black throughout, unlike Araneus diadematus. Sternum dark, unlike Neoscona. Dark band on middle of second-to-last segment of the rear legs, unlike L. cornutus. Difficult to distinguish from L. sclopetarius by the underside alone, although it more often has some red colour on the legs and is less likely to be found on man-made structures than L. sclopetarius.

Genus Araniella (Cucumber Spiders)

2 species in North America, 17 worldwide.

Araniella displicata (Six-spotted Orbweaver)


Photo © Stan Rullman

A tiny spider, often observed upside-down on a web just above the surface of a single leaf. Color of the abdomen variable, typically with a red rim, a yellow or green arc passing around the spinnerets, and yellow or green spots on a red background between the spinnerets and the legs. The colors and pattern range from very bright and distinct to quite dull and smeared. The photo above is about halfway between the two extremes. Legs unbanded. Sternum unmarked and slightly darker than the legs.

A northern-hemisphere species. The only species in the genus known from the US. Outside the US, easily mixed up with other species in the same genus.

Araniella proxima


Photo © Ryan Grow

Red patch at the tip of the abdomen, above the spinnerets. No red present elsewhere on the abdomen, unlike A. displicata.

A northern-hemisphere species. In North America, not found south of Canada, where it is the only species of Araniella known to be present besides A. displicata. In Europe and Asia there are more species in the same genus present.

Genus Cyclosa (Trashline Orbweavers)

5 species in Canada and the US, 179 worldwide. These tiny spiders often build a line of trash-camouflaged egg-sacks directly attached to their orb-web. Usually these appear as vertical lines, but some species make spirals or fan-shaped decorations.

Cyclosa conica (Conical Trashline Orbweaver)


Photo © catchang

A northern-hemisphere species. In Canada and the US it can be mixed up with C. turbinata. Around the Mediterranean Sea it can be mixed up with C. algerica and C. sierrae. In northern Europe there aren’t any other Cyclosa it could easily be confused with. Compared to C. turbinata, the largest pair of white patches on the underside of the abdomen nearly touch (C. turbinata’s are well-separated). The exact shape of the white patches vary considerably from one individual to another and from one geographic region to another (another example).

Cyclosa turbinata (Humped Trashline Orbweaver)


Photo © Justin Williams

A North American species. In Canada and most of the US it can be confused with C. conica. The largest pair of white patches on the underside of the abdomen are more widely separated than on C. conica, and may have a pair of smaller white dots or a short white line between them.

Genus Mangora


Photo © Matt Claghorn

Mangora are tiny and mostly found in wooded areas, and are thus less commonly photographed than Araneus, Larinioides, or Neoscona, but are quite common once you know where to look. With the exception of M. placida, they have a green sternum. All have relatively large hairs or tufts on their legs. The center of their web, where the spider rests, has a dense net with lots of small cells instead of the fewer larger cells in most species’ webs.

7 species in North America, 186 worldwide.

Mangora placida (Tuft-legged Orbweaver)


Photo © jawinget

An eastern North American species. Brown and black on the underside where other Mangora are green. Size, tufted legs, and web similar to other Mangora.

Mangora gibberosa (Lined Orbweaver)


Photo © Joe Bartok

An eastern North American species. Sometimes (but not always), creates an opaque circle or disc of silk to rest on. Web otherwise similar to other Mangora. Green sternum unlike M. placida. Black lines on undersides of legs close to the body, unlike M. maculata and M. spiculata.

Genus Nuctenea

3 species worldwide, all in or near Europe. Used to include the species which are now in the genus Larinioides.

Nuctenea umbratica (Walnut Orbweaver)


Photo © Taxon Expeditions

Has a pair of rounded white marks on the underside of the abdomen, similar to Larinioides, but perhaps a bit thicker, shorter, and closer to the mid-point of the abdomen. Sternum black.

Family Tetragnathidae (Long-jawed Orbweavers)

Genus Leucauge (Orchard Spiders and Allies)

3 species in North America, 167 worldwide. Generally found on horizontal orb webs instead of vertical ones.

Leucauge venusta (Orchard Orbweaver)


Photo © molanic

Orange V-shaped mark on underside of abdomen, point towards head, highly reflective from some angles but not others. Sometimes confused with Mangora due to generally green colouring and hairy legs. Unlike Mangora, the centre of Leucauge webs have a hole large enough for the spider’s abdomen to poke through. Found throughout the eastern US into Nova Scotia and southern Ontario, but not found in peninsular Florida. Occasionally found in the western US, particularly in the big cities of California. Observations south of the US are likely other species of Leucauge.

Leucauge argyrobapta (Mabel Orchard Orbweaver)


Photo © cynthabbott

Split from L. venusta in 2018. US range: Southeast US, closer to the coast. Range outside the US not yet clear, but likely found throughout Mexico and Central America down to Panama and not found in the Caribbean. May be confused with the many other species of Leucauge in Central and South America. Red/orange V-shaped marking on abdomen similar to Leucauge venusta, but with the arms usually thicker in such a way that they form a less-sharp point towards the head. Paired red/orange markings on the dorsal posterior abdomen can often be seen in ventral images - in L. venusta, the analogous markings are yellow or silver. Like L. venusta, the red markings are highly reflective.

Leucauge argyra


Photo © Bill Lucas

US range limited to peninsular Florida, with occasional specimens found in coastal Texas. Found throughout Mexico, Central America, the Caribbean, and at least the northern half of South America. No V-shaped mark on underside of abdomen, in contrast to the other two US Leucauge species.

Genus Tetragnatha


Photo © JeremyHussell

Easily identified to genus by the combination of very long, thin legs, long abdomen, and prominent jaws. However, there are 15 widespread species in N. America, and there is not much known about how to identify them from photos with the exception of T. viridis (it’s green) and T. caudata (long, pointy “tail” on the end of the abdomen that extends past the spinnerets, as opposed to the blunter end of the abdomen seen in other species). 330 species worldwide.

31 Likes

Fantastic post!

3 Likes

Thanks! It’s a work in progress. Additional content would be welcome!

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Orbweavers from above seem to be very variable within a species. Is the view from below generally less variable/more reliable for ID? If I see two such views in observations that differ in the pattern on the abdomen, is it conclusive that they’re not the same species, genus or family?

e.g.,
https://static.inaturalist.org/photos/19305814/original.jpg?1528381535
https://static.inaturalist.org/photos/11521908/original.jpg?1509362896

I would say the ventral view is much less variable, and for the majority of species it will be diagnostic. There will be some species where it isn’t though, so care needs to be taken.

With secondary characters (pretty much anything non-genitalic or eyefield) I would consider them in clusters, where the more you have the more certain you can be of the ID, but without dissection and/or genitalic structures you can never really be 100% certain.

Yes, I’ve generally found the undersides to be less variable than the top of the abdomen in most species. That doesn’t mean there’s no variation: a few species have lots, while the majority seem to have only one or two color morphs. Either way, it can be quite useful at times to have a shot of the underside to confirm the ID. And this guide exists because sometimes a shot of the underside is the only evidence available.

For the two photos you provided, I don’t recognize either of them, I’m afraid. The first one might be an Eustala. I haven’t really studied the undersides of that genus yet.

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I think it is all the more useful because most “Spider Books” will show you the dorsal view, and maybe a lateral, but they seldom show you the ventral, and as Jeremy states, ventral is often the only view one can get without disturbing the critter. For what it’s worth, a similar problem exists for lepidoptera, in that adults are well presented in books, but the caterpillars not so much.

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Thanks everyone. The two example pictures were both from different RG observations of eustala anastera. I was looking at these to compare to my own observation and found some variability in the ventral view of the RG observations. It looks like I’ll have to look a little deeper before drawing any conclusions.

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