Wednesday, October 1, 2014

Long-jawed Orb Weavers


We were sitting on a pond dock when someone spotted this creature stretched flat along a pole above the water.  Its slender length was dramatic enough that at first glance we weren't sure what kind of insect it was, but after counting its 8 legs we clinched the diagnosis as a spider.

Its posture and the jaws extending way in front of its head is a dead giveaway to its identification.  This is a Long-jawed Orb Weaver (LJO) of the family Tetragnatha (four jaws in Greek).  There are over 1,000 species found world wide, especially in the tropics, but only around 15 species in the US.  Identification of the species requires a specialist with lots of magnification to see parts that you and I could not identify. 

Also called "stretch spiders", LGOs extend their legs when threatened to hide on a blade of grass.  With their long legs and light weight body they are able to run on the surface of the water like a water strider. The third pair of legs which are much shorter are used to cling to grass or other vegetation as they stretch their other longer legs out in front and behind, blending in to the leaf blade.

Spread legs in a box
Even with a pocket camera you can still get decent pictures.  Using only a Panasonic Lumix camera with no specialized equipment you have to get your subject's permission to get up close.  I use a plastic box or container such as a margarine bin with smooth sides to keep the subject from climbing out.  If it is too active, a brief stay in the refrigerator will slow down the action.  You can see it has long jaws extending forward as well as the short third pair of legs.

"My what big jaws you have!"- note right fang.

Although named orbweaver, they are in a different family from the classical Araneidae orbweavers such as the Argiopes we discussed recently.  The Tetragnatha create their orb webs parallel with the surface of the water to pick up prey flying along the surface.  Their typical meal includes species like mayflies that emerge from their aquatic larval form into flying insects or insects that develop in the muddy banks like crane flies.

Front view - Note eyes, chelicerae with folded fangs
Once slowed down, I was able to move it into a different box to get the camera close for macro photographs. The eyes are now visible as raised black spots on the head.  The chelicerae (jaws) look blunt and club shaped, but you can see the fangs folded up along the inner edge.  Like a venomous snake, the Tetragnatha can control the amount of venom they inject.

Lip-locked mating - Youtube
Many female spiders are known to eat their potential suitors or even the male  after after they have mated.   The LJO has an interesting defense against this reproductive hazard.  They grab each others chelericia and holding on tight while the male delivers his vital fluids by using his pedipalps.  This gives a whole new meaning to the term "lip-lock".  You can see a video here but don't expect a lot of action.

More on LJW species at this website.