orchard spider   1 comment

what when where pic
orchard spider,tetragnathidae, leucauge, probably venusta 2009-07-05 bushes in front of our house

These spiders built their webs in front of our house for a while in the summer of 2009. I hope they come back in 2010 –they’re stylish and classy, and provided some of the best photographs I’ve ever taken of spiders. They belong to the family Tetragnathidae, the long-jawed orb weavers, so-called for the size of their chelicerae, I believe.

There were at least three separate spiders, all of them female. The webs were large, distinctive and well-constructed; they were constructed at an angle, rather than vertical. I don’t know why different spiders specialize in webs at different angles — the uloborid nearby built its web completely horizontally, which I’d never seen before. What’s the evolutionary advantage for that? The explanation I have heard involves building nests over water to catch rising prey, but that cannot apply here.

They rest in the web bottoms up, which explains why I have more ventral views of this spider than all the others put together. Here’s one to start, with its web:

From insects and spiders

Note the hole in the center of the web — that is characteristic of the family, and I do not think it is found in the other orb-weaver families (Araneidae and Uloboridae).

This next photo gives a wider view of the web: hole in center, special “dotted” web next, blank after that, then normal spirals. I’m not sure what the purpose is of this structure, and especially what the “dotted line” silk does. (I do know that this spider is ecribellate — in other words, is able to create sticky silk.) I would like to understand this aspect of the spider web better. It’s not clear if anyone knows why the webs are built this way.

From insects and spiders

Here’s one with detail of the ventral view, with the epigyne and the spinnerets marked. The spinnerets are where the silk comes from, whereas the epigyne is the female external sexual organ. It’s true what they say about spiders: you don’t want to be a male spider. The male spiders deposit their sperm into the epigyne with their pedipalps, which are sort of their antennae. You can see that that involves climbing below the (considerably larger) female, into a position where the hungry female can wrap her legs around the male and envenom him. Even if the female doesn’t really want to kill and eat the male, he is just so perfectly positioned as a morsel that I’m sure sometimes the temptation can be too much, and who can really blame her?

From insects and spiders

This photo is in a bit more detail and shows an interesting aspect of orchard spiders: each leg in the fourth pair has a set of fine hairs pointing forward from the femur, which are visible only if the photos get the light just right. This is pretty distinctive for this particular genus, as far as is known. I do not know what these hairs are for — I’m not sure if anyone knows. There’s a lot that we don’t know about these creatures — if you want to be an amateur scientist and push the boundaries of science, arthropods are a pretty good bet.

Also, some of the other photos I’ve seen to show a red spot on the bottom, below the yellow “U”. These photos don’t show this, so it’s probably variable. There were a bunch of other spiders at the time that in fact did have that red “half-hourglass” shape (which initially freaked me out, because I was worried they were Black Widows). These other spiders were smaller, and so were perhaps the males or juvenile females.

From insects and spiders

This photo has a dorsal view, and shows the beautiful markings they have. They are supposed to have a large yellow, orange or red spot on the rear, but that isn’t always found.

From insects and spiders

Wikipedia says that these spiders tend to get parasitized by a wasp larvae that attaches externally at the junction between the cephalothorax and the abdomen. This is something we would like to keep an eye open for in the future. We haven’t been able to find photographs of what to look for, though.

Here are some more photos, click for more detail:

From insects and spiders
From insects and spiders

Heres a photo that shows the red half-hourglass shape we mentioned earlier. It shows the same web pattern described earlier.

Finally, here’s a photo from bugguide.net with the eye pattern.

and another by Thomas Shahan on Flickr:

Orchard Spider Face - (Leucauge venusta)

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  1. Pingback: orchard spiders « A Little Wild

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