spidersrule

During the early summer back in 2015 I found that a few leaves of my backyard grape vines were covered with colorful galls.  After some research, I identified these galls as “grape tube galls” which were likely created by Cecidomyia viticola (AKA Schizomyia viticola) a tiny fly.  The gall growth is stimulated by the developing fly larva within the plant tissue.  Some species cause significant damage to the host plant, but in this case only a few leaves were affected, and any damage to my grape vine was insignificant.  In my opinion the galls were very beautiful.

A grape leaf with tube galls likely produced by a fly Cecidomyia viticola

As I was admiring the galls, a small flower fly (Syrphidae) landed on the edge of the leaf.

A grape leaf with tube galls likely produced by a fly Cecidomyia viticola with a flower fly (family Syrphidae) on edge of leaf (not the gall maker)

When I bent down to examine the tubes closely, I found spiders among the galls!

pair of meshweavers under thin webbing among tube galls

Some small spiders build their webs in the spaces created by curved leaves.  In this case, hiding below the thin whispy webbing stretched between the tube galls on my grape leaves were tiny brownish spiders.  I recognized them as meshweavers (family Dictynidae).  There are two species of meshweavers in my yard that I have found building very thin webs on the surfaces of leaves.  These two species Dictyna foliacea and Emblyna sublata are quite similar in appearance.  They are both small brownish spiders, in the females there is a light yellowish or orange colored folium (central stripe) on the abdomen.  One way to distinguish these females is a difference in the markings on the cephalothorax (head region). In Dictyna foliacea there is usually a single stripe of white hairs, in Emblyna sublata there are usually three separate white stripes of white hairs (sometimes more).

Both of these two species of meshweaver females are illustrated in my book (Plate 21) and I include those paintings by Steve Buchanan below.

comparison of female meshweavers Dictyna foliacea and Emblyna sublata paintings by Steve Buchanan

In this situation among the galls the residents were a pair of tiny meshweavers (Dictyna foliacea).  This spider seems to prefer the leaves of herbaceous plants in fields and brushy areas.  I usually encounter them on the upper surfaces of goldenrod or other plants in our home prairie patch.  The grape leaves with tube galls provided a convenient substrate for their web.

pair of meshweavers (Dictyna foliacea) in their web between grape tube galls

Perhaps the flash from my camera, or the fact that I was hovering very close to the leaf, stimulated the spiders to move.  Here are photos of the male, and the female after they moved at least a bit more into the open.

male meshweaver (Dictyna foliacea) in web

female meshweaver (Dictyna foliacea) at the edge of her web among grape tube galls

Here (below) is a photo of the similar looking meshweaver Emblyna sublata in her web atop a leaf.  These photos were taken during a bio-blitz in May of 2015 at a nearby park (Shale Hollow Park).  Notice that she has more white hairs on her cephalothorax (head region) than Dictyna foliacea.

typical form female of the meshweaver Emblyna sublata, scale bar 1/8 ” (appx 3mm)

Here (below) is another individual of Emblyna sublata photographed on at the same location and time as the photograph above.  She is an extremely dark colored individual with a very fat abdomen (probably full of developing eggs). She is busy eating.

dark form female of the meshweaver Emblyna sublata eating a prey item

Here is another photograph taken on the same day showing another pair, male and female meshweavers (Emblyna sublata) in their nuptial web.

pair of meshweavers (Emblyna sublata), male below looking up at female above him

In many cases, pairs of spiders have been found cohabiting the space under the web.  On one occasion while wandering in my yard I found a male with a fly prey. By the time I returned with my camera, the fly had been transferred to the female. Perhaps the male offered her the fly as a nuptial gift.  This sort of behavior is known for some spiders, but I was unaware that meshweaver males provided nuptial gifts.  Or perhaps the larger female just stole the fly from the male.

pair of meshweavers (Dictyna foliacea) in thin web on top surface of a goldenrod leaf in my back yard, here the male is on the left and the female is feeding on a fly prey

A slightly closer view of the same pair.

pair of meshweavers (Dictyna foliacea) in thin web on top surface of goldenrod leaf, female with fly prey

Even tiny meshweavers such as these can sometimes capture prey that seem huge in comparison to the spider.  On June 17, 2008 I found a female meshweaver (Emblyna sublata) with a fly that was very much larger than the spider.

meshweaver (Emblyna sublata) feeding on a large prey item (fly)

In this case she has bitten the fly near the base of the antennae, maybe this is because there is soft flexible cuticle on the fly at this position; making it easier for the tiny fangs of the spider to penetrate the exoskeleton of  the fly. Here is a closer view.

close view of a female meshweaver (Emblyna sublata) with a huge prey (fly)

There always seems to be something going on in our small back yard, all I need to do is to slow down and pay attention.  As I write this post it is winter, but I can still recall that early summer morning, when finding colorful galls on the leaves of my grape vines led me to an adventure observing meshweavers.

If you live in eastern North America there is probably a life-and-death struggle going on near you between the local spiders and a particular wasp.  The wasp is famous for its remarkable mud nests, the beautiful Pipe Organ Mud-dauber Wasp (Trypoxylon politum). This is one of the most frequently encountered predators of spiders in our region.  It builds conspicuous mud nests with a tubular shape that some people think resemble organ pipes (because of their varying length and parallel arrangement).

large array of Trypoxylon nest tubes said to resemble a pipe organ, note the holes (dark) where young wasps have successfully emerged out of their chambers

pipe organ pipes (this photo is shown upside down to emphasize the resemblance)

This wasp builds its pipe organ mud tubes to house her family.  The carefully constructed tubes are built of wet mud that she collects from the neighborhood. Each load of mud is added to the tube creating a series of ridges, looking almost like the coils of hand made coil-built pottery.  When dry, the tubes become quite hard and durable.

one dry tube with a newer wet extension and one fresh Trypoxylon tube

Trypoxylon female flying to nest with load of wet mud

Trypoxylon female landing at nest with mud

Trypoxylon female at nest adding mud to lip

Here is another series of photos of a female arriving with a mud ball and spreading the mud along the edge of the tube forming a new extension.

Trypoxylon female arrives with mud ball, male attending below

Trypoxylon politum female adding mud to her tube, male attending below

Trypoxylon politum female adding mud to her tube, male attending below

Trypoxylon politum female adding mud to her tube, male attending below

When a tube is ready, she will fly out and capture a spider. After she captures a spider, she paralyzes it with a sting, then stuffs it into the tube. The spiders aren’t dead, just immobilized.  They are alive and will remain so until they are eaten by the baby wasp (larva).  As she provisions her nest tubes, there is often a second wasp seen hanging around near the entrance.  This is a male Trypoxylon, guarding the female and her nest.  I assume he is likely protecting his mate from other males who might try to mate with her.

male Trypoxylon wasp guarding entrance to tube with female inside

fresh tube of Trypoxylon wasp with pair present, male visible at entrance

When the mother wasp has provided enough zombie spiders as food she will lay an egg on one of the spiders then seal up that section of the tube. The pair of wasps actually mate inside the tube and the male holds the female as she lays the egg.  The female now seals the zombie spider prey and her egg by making a mud partition.  Eventually each tube will have several compartments, each with a supply of paralyzed spiders and wasp eggs.

back view of Trypoxylon nest tubes revealing wasp pupal cases and some spider bodies (at left)

The egg will hatch into a larva and begin to devour the paralyzed spider.  As it eats, it grows and molts. The larva looks a bit like a maggot at this stage, munching through one “fresh” paralyzed spider after another and growing.  After eating the entire cache of zombies, the larva will construct a survival capsule called a cocoon and molt into the pupa.  At this stage the little wasp looks like a tightly folded pale mummy sealed in a brownish sarcophagus.

dissected Trypoxylon tube revealing successful emergence

In her article about the variable life history of Trypoxylon politum, Jane Brockmann has published a nice description of the life cycle of these wasps*.  The egg hatches in a couple of days, consumes the prey spiders in about five days, then spins a cocoon (which hardens into a dark brown capsule-shaped pupal case in a few days).  When metamorphosis into a wasp is complete, the young wasp emerges from its pupa and digs its way out of the mud chamber.  According to Brockmann, some of the young wasps emerge about six weeks after pupation, in the same summer.  Others enter a “resting stage” called diapause.  These individuals will spend the winter in the tube and emerge the following spring.

This wasp, aka Trypoxylon is skilled at capturing spiders out of their webs.  Her favorite prey are small orb-weaving spiders.  In the mud nests that I’ve dissected from around my house, the spider victim most often taken is Neoscona arabesca (aka arabesque orbweaver).  Sometimes the wasps also take immature Araneus marmoreus (aka marbled orbweaver) that are about 1/2 grown (roughly the same size as adult N. arabesca).  Perhaps the size is the critical feature that the wasp is using to make her choice.

dissected Trypoxylon tubes revealing dead spider bodies of Neoscona arabesca

Neoscona arabesca female (in her web)

So it is clear that this wasp is a real threat to the local spiders.  Imagine my surprise when I noticed one of the wasps (the male) hanging as a prey item in the web of one of the Common House Spiders (Parasteatoda tepidariorum) on the side of our house.

Common House Spider with male Trypoxylon wasp prey (also note that some of her spiderlings are emerging from another egg case above)

Somehow it seems like poetic justice to have a spider capture and kill a wasp that specializes in eating other spiders.  It isn’t clear to me that Trypoxylon is capable of capturing Parasteatoda.  The typical prey of Trypoxylon are orb weavers with their flat circular webs.  Thus the orbweaving spiders are exposed to direct attack.  In contrast, the web of Parasteatoda is a complex tangle of nearly invisible threads filling a three-dimensional space.  The spider hangs within this tangle.  For the wasp, it would be very difficult to approach the spider without getting tangled in the web, and potentially being captured. Maybe this is how this spider predator became spider food.  Here is a closeup shot.

Common house spider feeding on a male Trypoxylon wasp prey

Remarkable names are the rule in “scientific” terminology.  Sometimes they are used enough by enthusiasts that they become the “common name” for the species.  This is the case for both of these interesting animals.  The Pipe Organ Mud-dauber Wasp (Trypoxylon politum) is often referred to as just “Trypoxylon,” and the Common House Spider (Parasteatoda tepidariorum) is often referred to as Parasteatoda.

Reference:

Brockmann, H. Jane. 2004. Variable life-history and emergence patterns of the pipe-organ mud-daubing wasp, Trypoxylon politum (Hymenoptera: Sphecidae). J. of the Kansas Entomological Soc., 77(4): 503-527.