Friday, May 27, 2011

Some Small Spiders

Relatively small, compared to some heavyweights such as the Dark Fishing Spider.

This is an Elegant Crab Spider (Xysticus elegans). Not uncommon, but often overlooked due to their cryptic coloration, small size – this one is about 5 mm long, and their habit of staying low and living near the ground.

As often happens in nature, a predator has itself become prey. This female Elegant Crab Spider has captured a predacious Carabid beetle.

Robber flies are fearsome hunters in their own right but this one has been captured by a Jumping Spider. Despite the distinctive markings on the abdomen I haven't been able to get a better I.D. on this spider than possibly Phidippus clarus.

This unknown spider at BugGuide.Net looks the same but there's no consensus as to species. To make life a little more complicated ... Phidippus clarus can have different color forms, and it's also possible that my photos are of an immature specimen, which can look very different from an adult.

There seem to be dozens of different kinds of jumping spiders lurking on the vegetation. I don't know what this robust little female is either.

Insects aren't the only arthropods that have fatal encounters with spiders, sometimes it's other spiders. The large pale spider is about 10 mm long. It's a Slender Crab Spider (Tibellus sp.), and this time a Jumping Spider's turn to play the role of the hunted.

A Flower Crab Spider (Misumena vatia) lurks on vetch.

The spider's patience has paid off. Though larger and possessing a stinger the bumblebee never had a chance, as the venom of these crab spiders is specifically toxic to bees.

Excluding its legs this Long-jawed Orb Weaver (Tetragnatha sp.) is about 15 mm long and can easily mistaken for a grass seed when at rest.

This mug shot is about the best detail possible with a subject so small (good lighting really helps!). The appellation "long jawed" certainly fits. Note what looks like globules on the ends of stalks: this spider is a male and the balls are sperm packets on the ends of its pedipalps. (The pedipalps are the two "feelers" at the front of a spider – they are not true legs).

Most orb weavers spin a new web daily, abandoning the old one. Almost invisible, these webs often entangle unwary victims such as this Four-spotted Skimmer.

The following three images were acquired indoors under poor lighting so they can't do justice to the eye-catching color scheme of this female cobweb spider. It's about 5 mm long, and the abdomen is black with silver markings. This is (probably) a Triangulate Cobweb Spider (Steatoda triangulosa). A welcome guest in many homes, as it is known to prey on fire ants, ticks, and spiders whose bite is harmful to humans such as the Hobo Spider and the Brown Recluse. With the exception of ticks none of these other arthropods are extant in this area, so a wasp moth will do for lunch ...

As I was taking photos of this Wolf Spider (Lycosa sp?) it seemed like something looked wrong with its abdomen. Zooming in on the image later showed what was amiss ... this is a mother spider with her young hitching a ride on her back. They will stay with her for a few weeks until they are old enough to fend for themselves. Small spiders indeed ...

Goldenrod Gall Fly (Eurosta solidaginis)

During the summer months round galls are a common sight on goldenrod. One cause of galls is insect larvae, which produce chemicals to induce the abnormal growth. The hard exterior of the gall provides a safe haven and the inside becomes a source of food.

Many kinds of insects (as well as mites and fungi) cause galls, often unique to each species on preferred host plants (more on this subject at BugGuide). Here's the culprit responsible for the round goldenrod galls: a member of the Fruit Fly family, the Goldenrod Gall Fly (Eurosta solidaginis). There's no sign of an ovipositor on this insect, which tells us that it's a male.

This fly is roughly 8 mm long (the measurement is by "rule of thumb", metaphorically speaking).

Adult flies are emerging in greater numbers every day so it was just a matter of time before I stumbled across a female (note the ovipositor) ...

... and a mating pair.

Images of females ovipositing, starting the cycle anew.

Until I took photos of this fly a few days ago and researched its life cycle on the Internet I had no idea as to the cause of the goldenrod galls. And I had always assumed that winter and early spring (when no self-respecting insect would be active) galls with holes in them were the result of predation by Downy Woodpeckers. Perhaps not: it seems that the fly larva prepares its emergence tunnel in the autumn before pupating for the winter. You learn something new every day ...

About eighteen months after posting the photographs above I've learned that there's more to the life story of the Goldenrod Gall Fly. It appears that my original surmise about the opening in the gall seen in the image above was probably correct and the cause is predation. The larva prepares an exit passage in the autumn – but – it does not chew all the way through the gall, it leaves the outer integument (epithelium) intact to provide some protection from the elements.

There were actually two larvae ensconced within the gall in the following photo. When I opened it I fortuitously split one of the exit tunnels (circled and labelled in red) right down its length. I don't have a picture of the other larva that was living in the center of the gall (its passage, which goes into the gall at a right angle to the plane of the cut surface, is annotated in blue) – it wasn't so lucky and fell victim to my jackknife.

Closer views of the larva and its exit passage.

This is the larva (about 5 mm long) in my hand, I'm not sure which end is the head. According to the Eurosta solidaginis page at BugGuide.Net pupation occurs in early spring, so I'll have to re-visit the goldenrods in a few months and check out the pupae. In the meantime, there's some fascinating information about this insect's winter survival strategies at: Which Way Out – A Study of the Exit Tunnels made by the Goldenrod Gall Fly, Eurosta solidaginis.

The conclusion of a story that began two years ago – these final three photos of the pupa of the Goldenrod Gall Fly were taken and uploaded in early May 2013. I haven't determined the earliest that pupation takes place, but I have found some in mid-April.

Wednesday, May 25, 2011

A Fetch of Dragonflies

In case you've ever wondered what a group of dragonflies is called ...

About a kilometer east of Tweed "the Trail" crosses a sand bottomed creek. Pools of standing or slowly moving water in shady forested areas are combined with open sunlit patches created by the trail. This medley of habitats, very different than the river, lake or marshes, has its own collection of odonate species.

While it was on the wing I mistook this immature female Chalk-fronted Corporal for a species of Baskettail. Although this one is perching on a twig these small dragonflies (40 mm long) are more often seen sitting on the ground or on rocks.

Habits can be a good way to identify or at least narrow down dragonfly species. Springtime Darners (Basiaeschna janata) prefer to hang vertically when resting. At about 60 mm in length it's relatively small for a darner. The colors and markings of the males are the same as the female's.

The Stream Cruiser (Didymops transversa) is about the same length as the darner above but much more robust. This dragonfly's habit of perching on an angle, like the female in the next two photos, is typical of its species.

Both of our two local species of cruiser have a pale facial stripe and only one lateral thoracic stripe, making them easy to spot in the field ... other large dragonflies, such as darners, have two thoracic stripes (if any).

Male and female Stream Cruisers are similarly patterned. The male can be distinguished by its slightly flared abdomen and pale claspers.

A mating pair of Stream Cruisers

This is an immature female Mustached Clubtail (Gomphus adelphus). The markings and length (at 45 mm it's small for a clubtail) agree with the species account in my field guide. The colors threw me off at first, but eyes will turn green and the bright yellow on the body will change to grayish-green as the dragonfly ages.

The "7"-shaped pale marks on the upper thorax, the broken middle thoracic stripe, and particularly – the heavy black markings on the face – are the characteristic field marks of this species.

Many species of clubtails prefer to stay low when at rest, adopting a horizontal position on the ground, rocks or leaves like these two immature males. In the field males can be differentiated from females by their clubbed tails and claspers, visible even from a distance on the male to the right.

A closeup of an immature male's facial markings. Clubtail species can be hard to tell apart and it's often necessary to get a detail shot of the terminal appendages for a positive I.D. In this case the bold black cross-stripes on the face are sufficient.

An older male Mustached Clubtail ... this photo was taken about one month later than the others. Note the changes in color.

Obvious field marks aren't good enough to sort out three of our local Baskettail species, all are similarly patterned and about 45 mm long. The only noticeable difference between them is the amount of pigmentation at the bases of the hindwings (which can vary) and the presence or absence of a "T"-shaped spot on the top of the frons (no images of the latter, the dragonflies weren't co-operating). So let's have a closer look ...

Baskettail # 1
The hindwings have a generous amount of black at their bases.

Looking at the terminal appendages: we see that the cerci are constricted at their bases but there's no evidence of any teeth. Taken in conjunction with the relatively large amount of hindwing pigmentation we have to conclude that this dragonfly is a Common Baskettail (Epitheca cynosura).

Baskettail #2
Some black pigmentation is visible at the bases of the hindwings.

Views of the claspers from a couple of slightly different angles. A ventral tooth is barely visible in the first image, but this isn't necessary for an I.D. What is clear in both photos is that the cerci turn down at the ends, and – they definitely possess dorsal teeth. This is sufficient to identify this dragonfly as a Beaverpond Baskettail (Epitheca canis).

Baskettail #3
The hindwings have a small amount of pigmentation at their bases.

A dorsal view would be helpful but it's unneccessary because luckily I was able to obtain a good image of the claspers – the cerci definitely have a sharp ventral tooth. As always, the claspers are the final word as to species. This dragonfly is Spiny Baskettail (Epitheca spinigera).

A teneral male Brush-tipped Emerald (Somatochlora walshii), length about 45 mm. As a rule it's not a good idea to handle a teneral odonate, especially by its delicate wings. But this one is gravely injured (likely by a beaver, a dog or a hiker) and won't survive much longer. A pity this dragonfly in such rough shape, as it would have made an excellent subject with its amber-tinted wings and a thorax that looks like it's made out of colored metal foil.

The hairy claspers (which sustained injury as well) are visible in the field and leave no doubt as to the identity of this dragonfly.