Friday, September 2, 2011

New address

Hi all, I have moved my blog to a different address! From now on new posts will be at:

Thank you!!

Monday, August 8, 2011

Spiders in Seattle: a walk through the Washington Park Arboretum

Last week I went to Seattle with Ryan for a family reunion. We spent Thursday afternoon exploring the Washington Park Arboretum, a very pretty park containing all sorts of exotic-looking plants, including magnolias, asiatic maples, rhododendrons and camellias. It didn't take long to notice that the vegetation supported many spider webs, and that the abundance of spiders was noticeably higher than in Logan.

Washington Park Arboretum

The first spider I found was an araneid of the genus Zygiella, an exciting find since I had never photographed this genus before. Zygiella spiders have a relatively flat, oval abdomen, and eyes that are closely spaced. The back of the abdomen has a leaf-shaped pattern (folium) that is generally white in the front and dark in the back. The orbweb built by adults is interesting because it typically has a missing sector on the upper half, in the direction of the spider's retreat. The missing sector is where the safety line is located, and this thread leads from the hub of the web to the retreat, as seen in the pictures below.

Zygiella close to her retreat

Zygiella leaving her retreat to go on the safety line 

Not far from the Zygiella web, I noticed a silk tent under which a small spider was guarding her eggs, which she kept in a round sac. I only got one picture and did not try too hard to identify her, as I didn't want to disturb her. 

A female web spider guarding her eggs

A tangle-web under a leaf revealed a theridiid (probably in the genus Theridion) with a branching pink median stripe on the back of its spherical abdomen. This spider reminds me of Theridion pictum, a species that is found in Europe, North America and Africa.

The most conspicuous spider in the park was the Cross Orbweaver, Araneus diadematus. The webs of this spider were everywhere, even outside the park, in people's yards. This is the same species than the one mom found in our yard in France (see previous post).

Araneus diadematus

I found a tetragnath spider of the genus Metellina, sitting in the center of a web, in a shrub relatively low above the ground. Tetragnaths, which are also known as Long-jawed Orb Weavers because of their typically long chelicerae, build orb webs that have a "hole" in the center. Their webs do not have a safety line or a retreat as described for the araneid Zygiella. There are only three species of Metellina in North America. The one I found was probably Metellina segmentata, a species introduced to Canada from Europe and first found at the northern edge of Washington in 1986.

Metellina segmentata

The underside of Metellina, sitting on the empty hub of her web.

As I was walking by some vegetation low on the ground, I noticed that most of it was covered in sheets of silk. I took a closer look and found that these were funnel-shaped webs built by spiders in the family Agelenidae, which are also known as Funnel-Web Spiders. The notorious Hobo Spiders belong to this family. These spiders usually sit inside a funnel-shaped retreat, but when they detect the vibrations caused by trapped prey, they quickly run across the sheet of silk to bite the victim. I tried to get one of these spiders out of its retreat by gently poking the sheet web. The spider came out so quickly that it startled me!

Agelenid spider waiting inside the funnel of its web

The agelenid runs out in response to vibrations in the web

Ryan found a philodromid spider on a bench, at the base of the armrest. Philodromids are active hunters that do not rely on webs to catch prey. This spider appeared to be guarding her eggs, which she had covered in a protective layer of silk. She did not move away from her eggs, even when I got very close to take a picture.

Even benches can provide good habitat for spiders!

Philodromid spider guarding her eggs

I was excited to find the spider below in the rolled-up leaf of a shrub, although it is a species introduced from Europe. The spider belongs to the family Theridiidae, and the species is Enoplognatha ovata, a spider with yellow-white legs that varies alot in color and pattern. This individual had two pink stripes with small dark spots, on a cream-colored abdomen.

Enoplognatha ovata

In a shrub nearby, I barely noticed a tiny tetragnath spider, holding onto the underside of a leaf, its long and slender legs stretched out in an attempt to blend in with the nearby vegetation. Many members of this family are characterized by these very long legs.

A small tetragnath resting under a leaf

After walking under a bridge to get to the other side of a busy road, I inspected the outside walls of the bridge and found a couple of big Larinioides sclopetarius sitting in their webs. This spider, also known as the Bridge Spider, or Gray Cross Spider (family: Araneidae), prefers to build its web on man-made structures, especially near water. Apparently, it is rarely found on vegetation. In both sexes, the cephalothorax has conspicuous white markings, as seen in the picture below:

Larinioides sclopetarius on a bridge wall

Wednesday, August 3, 2011

A french Araneus

Mom sent me a picture of a spider that we get every year in our backyard in Brittany, France. This spider, which she photographed in the shrubs by one of the yard fences, is an orb-weaver of the genus Araneus. The species appears to be diadematus (a.k.a. Cross Orbweaver, or Garden Spider), as suggested by the elongated white spots in the front of the abdomen that are arranged in the shape of a cross. A. diadematus is common in Europe, but it can also be found in parts of North America.  Females usually sit face down in the web, or hide in a retreat near the web. The retreat is connected to the web by a special silk line so that the spider can quickly move between the two locations. The abdomen of A. diadematus has two "shoulder humps" in the front, as seen in the picture below. The back of the abdomen has a leaf-shaped pattern (folium) with scalloped margins. This species varies in color and in markings (the "cross" in some individuals is sometimes indistinct).

 Araneus diadematus with prey item wrapped in silk

Sunday, July 31, 2011

In search of the elusive Argiope

This morning, Lori Spears, Ben Kuethe and I went to a field located not far from Thatcher, a small town west of Tremonton. Someone had told Lori that there had been large amounts of Argiopes last year in this field in the late summer. Although this genus in the family Araneidae can be quite common in the right type of habitat, I had not seen it yet in the U.S. We followed the instructions to get there, eager to find some big Argiopes.

The field consisted mostly of grasses, thistles, and a few small shrubs:

We walked around for quite a while without seeing any spiders at all, until we came across a couple of large orb webs. The occupants turned out to be Aculepeira spiders, which are in the same family as Argiope. These Aculepeira were big and appeared to be well fed, as suggested by the prey items caught in their webs. The abdomen of Aculepeira is typically egg-shaped, widest anteriorly, and has a dorsal longitudinal lobed band.

Only two or three species of Aculepeira can be found in North America. According to Levi 's publication The orb weaver genera Metepeira, Kaira and Aculepeira north of Mexico (Araneae, Araneidae), the species we found was probably A. packardi, as suggested by the posteriorly directed lobes on the back of the abdomen. I have collected this species at my field sites in Logan Canyon, but I had not seen any as big as the ones here. Adult A. packardi females build a new web every night and actively remove prey caught during the day.

Aculepeira  resting on thistle 

Aculepeira sitting in the hub of her web with a prey item

Aculepeira working on a large prey item

Aculepeira has a typical median ventral white streak, as seen in the picture below:

As we were discussing why we did not find any Argiopes yet, Lori found a small Argiope trifasciata in its web, not very far above the ground! This was the only one we were able to find, but it was a pretty spider that made our trip worthwhile.

Lori finds an Argiope

Argiopes sit on the web with their head facing downwards, and their legs are often held in pairs. Argiope trifasciata is also known as the Banded Garden Spider. The back of its abdomen is a silvery/pale yellow background, with several horizontal black stripes, and the legs are striped. We think our spider was immature, as it was relatively small and had a mostly white dorsal surface.

I have read that Argiope trifasciata prefers to orient its web along an east-to-west axis, with its abdomen facing south. Given that the underside of A. trifasciata is mostly black, the orientation of the spider is supposed to maximize solar radiation and heat gain, which is an important consideration for spiders that are active late in the year.

Argiope trifasciata

The dark underside of A.trifasciata

We decided to return to this site in about a month, in hopes of finding adult Argiopes.

Wednesday, July 20, 2011

Dreaming about Colombia, part 1: El Paujil reserve

In 2008 I went to Colombia to visit my family in Bogota and to spend some time in a couple of reserves that belong to the Fundacion ProAves, an NGO dedicated to the conservation of birds and their habitats. I had such an amazing time there that lately I have been longing to go back. While I wait for my next colombian adventure, I decided to post some spider pictures from that trip. The amount and diversity of spiders in these reserves was staggering, making these places a dreamland for arachnologists. There were spiders and spider webs everywhere!

El Paujil is a  reserve dominated by rainforest, located in the departments of Santander and Boyaca. I spent a few days there, dedicating all my time to observing all the plants and animals I could find. I found it exciting to think that there are probably many undescribed species in this part of the world. We spent nights in a nice wooden cabin in the reserve. One of the first spiders I found was the one below, behind the cabin:

At lunch time, I noticed this small Argiope (family Araneidae) near the base of a tree. In North America, these spiders are known as Garden Spiders. Argiopes build orbwebs with a special silk structure in the middle called a stabilimentum (see picture below). The pattern of the stabilimentum varies across species, and the role of this structure is subject to debate.

Argiope sitting on the stabilimentum of it web

I also noticed this pretty jumping spider, which was wandering on a wooden post close to our lunch area:


My last find at lunch time was this araneid spider, which I found hidden in a rolled-up leaf. The silk structure at the tip of the leaf had called my attention. This spider had a roughly triangular shape, with several humps on the posterior part of her abdomen.

Along one of the trails in the reserve, I found my first Micrathena spider. I was so excited to find it but a little frustrated because I felt a little rushed as the rest of the group kept on walking. In addition, my camera lens had gathered condensation due to high humidity levels. I was able to take one acceptable picture. Micrathena spiders are araneids (they build orbwebs) that have a typical arrow shape due to the spiny projections on their abdomen.

On the side of a more open trail, I noticed many spiders like the ones below. Their translucent legs were hard to notice against the background vegetation. I think these were oxyopids, a family also known as the Lynx Spiders, due to their hunting strategy which consists in jumping and running after their prey, and their relatively good eyesight. I was able to take pictures of some spiders that had caught a prey item, including a fat caterpillar. Oxyopids have spiny legs, as seen in these pictures.

A red jumping spider caught my attention along another trail. It was very active and curious, and jumped on my camera a couple of times to investigate it. I had to place him back on the plant to take more pictures.

I found this other jumping spider in a very shaded area, where the canopy was dense:

One orbweb along the trail had a pretty spiral shaped stabilimentum. In an attempt to find out who had built this web without scaring the spider away, I carefully placed my camera behind the web and took a picture at random, hoping that it would be in focus. My strategy worked and revealed that there indeed was a spider hiding under the stabilimentum, but I can't tell what spider this was.

One section of the trail was in close proximity to a river. Upon inspection of a big log, I noticed this beautiful orbweb spider. I had never seen this species before, but I think it may be a tetragnath spider of the genus Leucauge. Members of this genus have a cluster of long trichobothria (these are hair-like structures that detect vibrations) prolaterally at the base of their femurs on their fourth legs. These trichobothria are noticeable in the picture below. The second picture shows the orbweb, with relatively few radii and a "hole" in the center, which are typical tetragnath web characteristics.

Also by the river, we found this Pisaurid spider (also known as Fishing Spider) resting on a small tree trunk. These spiders are able to stay underwater for a few moments. They feed mainly on aquatic invertebrates and sometimes on small fish.

At night time, my cousin Esteban, Ryan and I went out exploring not too far from our cabin. We were rewarded with a small tarantula, which was wandering about right next to the steps that led to our cabin.  Tarantulas have fangs that point straight down, whereas other spiders have fangs that cross each other.

Tuesday, July 19, 2011

Meanwhile, back in France..

My mom sent me a couple of pictures of a spider she found in our house, in Brittany, France. This spider, which belongs to the family Pholcidae (cellar spiders), genus Pholcus, brings back memories from home, as I remember seeing these when I was younger. I remember throwing small paper balls in their webs to see if the spider would mistaken them for prey items. Instead, the spider would shake and vibrate in its web. I later found out that this shaking is a defense mechanism which makes the spider look blurry and therefore more difficult to catch.

This spider was surrounded by her offspring, which first looked like small dots in her web:

The second picture shows the same spider and her young, now a little older:

Pholcids are long-legged spiders that hang upside down in tangle webs, which they typically build in dark areas (cellars, caves), but sometimes also in warm areas inside houses.

Sunday, July 10, 2011

Payette river rafting trip

My friends and I went to Idaho for a few days of great rafting on the Payette river. We stayed at a nice campsite not far from Crouch, a small town that had the craziest 4th of July fireworks I had ever seen. Our campsite was located by the river and had enough trees to provide shade...and interesting spider habitat. I searched for spiders a couple of times between our rafting adventures.

 View of the river from our campsite

My first find was this dictynid spider, which did not look like the dictynid species at my field sites in Logan Canyon (Utah). I had to gently poke her out of her tangle web to get a better look.

Close to the river, I noticed a male linyphiid spider in a sagebrush shrub. This spider was hanging upside down in its sheet-like web. When prey get caught in the web, linyphiid spiders bite them through the web while remaining upside down.

Anneli and Andy found this spider on the ground by our kitchen area. I have not seen this very cryptic looking species before, but I would guess that it is a philodromid spider, as it looks like a darker version of Philodromus histrio, a species common on sagebrush in Northern Utah. Philodromids are wandering spiders that do not rely on webs to catch prey. This family resembles the true crab spiders (Thomisidae) but philodromids have legs that are subequal in size whereas thomisids have third and fourth legs that are shorter than the first two pairs of legs.

One night, as we were chatting by the campfire, we noticed a small arthropod running around by our feet. Upon closer inspection, it turned out to be a solpugid!! Solpugids are also known as camel spiders but they are not spiders- they are a closely related order of arachnids. I was very surprised and excited to see one here, because I thought they were only found in desert areas. I guess that's not the case! Solpugids are typically nocturnal predators that use their impressive chelicerae to macerate their arthropod prey. I have heard that very little is known about solpugids because they are not easy find and difficult to keep in captivity. Perhaps this individual was hunting for arthopods that had been attracted to our campfire.

Solpugid hunting next to our campfire

That night I went to bed a little after midnight. As I was starting to fall asleep in my tent, I felt something walking on my arm. I turned on my headlamp and saw something hop straight onto the light! It turned out be a Phidippus jumping spider. I took a quick picture of it, let it out of the tent and went back to sleep. Jumping spiders are diurnal predators, but it has been shown that they sometimes use artificial light to hunt at night. This paper by Frank (2009) has some information on the subject:

Frank KD (2009) Exploitation of artificial light at night by a diurnal jumping spider. Peckhamia 78.1:1-3

Phidippus attracted to my headlamp. Picture taken after midnight.