Orbicularians are related families of spiders that either spin orb webs or are derived from spiders that probably spun this type of web or its immediate ancestor. Everyone is familiar with the classic orb web. Typically a number of anchoring threads cross each other upon which a silken spiral is imposed. In araneids and tetragnathids (see below) the spiral has a special type of sticky silk (called viscid silk). By contrast, uloborids make orb webs that use cribellate silk (a material that superficially resembles velcro but unlike velcro is sticky -- and sticky in a way very different from araneid silk) to catch insects. In general, these webs appeal to us for their regularity and economy. Whether they use viscid or cribellate silk, their placement makes them especially well-suited to capture flying insects, although some groups such as the insects and moths have evolved counter measures (wing scales that sometimes allow the insect to slip of out the web and leave the scales behind). It is hard not to marvel as one watches these spiders run their lines across large gaps in vegetation and then precisely produce their spiral structures. It is at least as interesting to watch those that make less regular or very different webs and think about the relative advantages of each. |
Please note that all images are copyrighted by the person who submitted them. To see an enlarged version of any image, click on the image. A separate window will open showing the larger image. |
|
Uloboridae -- these are orb-weaving spiders that possess a cribellum and calamistrum and use sticky cribellate silk to capture their prey.
|
Uloborus sp.
© Copyright 2001 by Bryan E. Reynolds
|
Uloborus glomosus
© Copyright 2006 by Jerome Rovner |
|
Deinopidae These cribellate spiders spin a small web which is held between their first two pairs of legs (see photo). The spider commonly hangs from a scaffold web. When attacking prey, the legs holding the web are spread to put the sheet under some tension. If the prey is on the ground or substratum beneath, the spider rapidly lowers itself from the scaffold web towards the prey and ensnares it. If the prey is flying, it sweeps its web at the prey. |
Deinopis sp.
© Copyright 2000 by Fred Coyle |
Deinopis longipes
© Copyright 2005 by Joseph Warfel, Eighth-Eye Photography |
|
Araneidae (orbweavers) These familiar spiders lack the cribellum and calamistrum that is primitive for the araneomorphs. They are termed "ecribellate". There are many species in this highly successful, world-wide distributed family. Most make vertical webs, others spin small horizontal webs and members of one genus (bolas spiders) produce chemicals that attract certain species of male moths -- the moths are then captured by a sticky ball of silk on a line that the spider throws at them. A relatively small number of species make no web at all. The sticky silk used by these orb weavers is quite different in source and mode of action than the cribellate silk made by uloborid (above) orb weavers. |
|||
Argiope aurantia
© Copyright 1997 by Bill Welch
|
Argiope aetherea
© Copyright 2006 by Jerome Rovner |
Argiope savigyni
© Copyright 2000 by Fred Coyle
|
|
Argiope argentata
© Copyright 2000 by Fred Coyle
|
Araneus pima
© Copyright 2001 by Bryan E. Reynolds
|
Araneus pima
© Copyright 2001 by Bryan E. Reynolds
|
|
Micrathena brevipes © Copyright 2000 by Fred Coyle |
Micrathena sagittata
© Copyright 2006 by Jerome Rovner |
Micrathena cyanospina
© Copyright 2006 by Jerome Rovner
|
|
Gasteracantha cancriformis
© Copyright 2006 by Jerome Rovner |
Eriophora pustulosa
© Copyright 2006 by Jerome Rovner
|
Alpaida sp.
© Copyright 2006 by Jerome Rovner |
|
Caerostris sp.
© Copyright 2006 by Jerome Rovner |
Unidentified araneid
© Copyright 2000 by Fred Coyle
|
Arkys sp.
© Copyright 2006 by Jerome Rovner |
|
Tetragnathidae (long-jawed orb weavers) These orb weavers are closely related to the araneids (above) but differ in several anatomical features. Also, unlike araneids, the majority of which build vertical webs, many tetragnathids make horizontal webs, some species locating them near water. However, other tetragnathids (e.g., Nephila) do build vertical webs. |
|||
Tetragnatha elongata
© Copyright 2006 by Jerome Rovner
|
Leucauge sp.
© Copyright 2001 by Bryan E. Reynolds
|
Nephila clavipes
© Copyright 2006 by KN Prestwich |
|
Theridiidae (cobweb weavers) -- These spiders make irregular webs (lacking spiral structure) that feature irregularly placed sticky silk threads. When prey becomes entangled in this silk, the thread tends to break and the prey swings as part of a silken pendulum towards the center of the web and more silk. These spiders hang upside down in their webs (see photo). Although famous for the widows (Latrodectus), there are many genera and species of theridiids found in North America and world-wide. |
Latrodectus hesperus
© Copyright 2001 by Bryan E. Reynolds |
|
|
Linyphiidae (sheetweb weavers) -- this is a large, taxonomically difficult, ecribellate family of generally very small spiders. They often are noticed when dew is on their webs. The webs consist of one or more horizontal sheets that are supported by vertical threads. It is common for the spider to rest underneath one of these sheets and attack prey that land or fall onto the top surface. |
Pityohyphantes costatus
© Copyright 2006 by Jerome Rovner |
|
|
This photo gallery is brought to you by members of the AAS and other arachnologists. last modified March 27, 2006 |
||||||