Monday, 16 September 2013

Do adult female house spiders roam?

As you gather from my last post, it is quite common to come across adult male house spiders, Tegenaria, roaming in search for females in late summer and autumn. Females are supposed to wait for them at the bottom of their web funnels. I was puzzled to find this fully grown, beautiful female inspecting my cat scratching post, in the open, an hour ago. Do females roam too?

Sunday, 15 September 2013

Spider portraiture

It is quite flattering that several people have congratulated me over the years on the invertebrate photos I feature in BugBlog, thank you guys! I don't claim to be a photographer, but I am happy to share a few tips on the white bowl technique, which I regularly use on critters found around the house and garden, especially on non-flying ones. As today I found the first male house spider, Tegenaria sp., of the season, I thought a post on this topic was timely.
Before my daughter finished saying 'spider!' I got the little beast running across the kitchen floor into a little plastic pot. For this, I save any little plastic pot I come across. You know the onion salad pot from an indian takeaway? ideal! To hold the bug for a few minutes the pot does not even need to have holes on the top. I also have a 'proper' bug viewing pot (like the one featured in the photos below). My bug pots are always available on the side of the kitchen and I always carry one in my bag.
The second piece of equipment is the bowl. A flat-bottomed white bowl, like those used for soup, is ideal, as its sides help reflect the light. Better if there is a smooth transition from the bottom to the sides, as it will reduce undesirable reflections.
 I take the bug pot and bowl to the conservatory (or outside, weather permitting), as I like as much natural light as possible.
And push the cat out of the chair (sorry!).
 Then I remove the lid of the bug pot, put the bowl on top, turn it round to transfer the spider to the bowl surface.
I'd like to say that, although it is a common technique, I don't like to use the fridge to cool down the animal, I am impatient and I want to get the photos and release the animal as soon as possible. Many of the bugs are naturally slow and settle quickly on the pot, or stop long enough for the shots. Male spiders at this time of the year are challenging, as they are very jittery and require a bit of attention until they are posing well. Usually, tapping on the table will startle them and they will stop running around. Unfortunately, they often stop leaning on the side of the pot, so when you remove it, they are settled in awkwardly like so...
...which is not ideal. I move the pot slowly until the spider is in the middle and blow softly under the pot, until the spider spread its legs.
Now lets go to camera settings. I don't own a DSLR, just a bridge camera (Canon Powershot G12, if you are wondering), but you can achieve a similar effect with any portable camera. I first set the flash on, and increase the flash setting to +2, this is important if the bug is dark, as the auto flash setting will result on an overall dark animal and not a very white background. You might need to experiment with your camera to find the best flash setting.
No flash
Flash on to +1
Then I set the focal point to the top left hand side of the visual field (nearer to the flash itself), instead of the central position. This ensures the animal is not in the shade of the objective. If I didn't do this, once I cropped the photo, the bottom right corner would be grey, not white, as it would be shaded by the objective. You can simulate this on a cameral without this setting by focusing in the middle point and then moving the camera trying not to lose the focus so that the animal is located in the top left hand side of the visual field.
 Today, I experimented by holding the camera vertical, so that the flash light came exactly in front of the spider.
Set the camera to macro, and fire away. I usually take lots of photos, as I want to get the focus right on the animal's eyes and I try also several angles, which are often useful for ID purposes.
  I download the photos in the computer and do some basic processing. Crop the white/grey space out, adjust the levels so that the white background is actually white, remove specks of dust or dirt and sharpen a little. That's it!
White level adjustment
 This one is my favourite of the session today. Although the white background is not perfect, as it is greyer on the right hand side, I like the spooky effect of the spider leg shadows.

Monday, 9 September 2013

Wandering Lime Hawkmoth caterpillar

From mid August to mid September is prime time for squished Lime Hawkmoth caterpillars. Being ready to pupate, they leave the lime trees where they have fed all their lives in search of a suitable pupation site on the ground. As lime trees like streets and parks, I always find them crossing the paths, and most often than not, already squished by passers by. Keep an eye on them, they are as large as a pinky finger when fully grown, greenish to pinkish colour, and with a blue 'horn' at the rear end. We collected this one, which we found on the school grounds this afternoon, to watch the rest of its life cycle at home.

Sunday, 8 September 2013

The weird and wonderful Vapourer Moth

While having lunch, a bright, russet moth outside flew against the bay window glass again and again. After a while, I decided to capture it to check what it was. The moth was very unsettled, and carried on flying in the bug pot while we finished our meal. Shortly after, another similarly russet moth, a bit larger, flew against the glass and landed on a silky cocoon on the window frame. I went out and realised the reddish moths were in fact male vapoureurs attracted by a female on the cocoon. The second male was now mating with the female (above). The Vapourer, Orgyia antiqua is a very odd moth indeed. They have a striking sex dimorphism. Males have large, feathery antennae and often fly during the day. They are a rich russet colour with a white spot on each forewing. Females, in contrast, don't look much like moths, they cannot fly as their wings are vestigial, they have small antennae and enormous bulging bodies, full of eggs, and are pale grey in colour. Females will barely move in their short lives, attracting the males with pheromones they release shortly after emerging from her cocoon. The large feathery antennae of the males helps them locate the females quickly.
I took this photo from inside the house.
After mating for about 15 minutes, the male left (13:20). We could then had a closer look at the female. Eggs were visible through her thin abdominal skin. She looks velvety and heavy.
The female quickly started to lay eggs on the cocoon surface, the photo below taken at 15:15. Note that the caterpillar hairs, which are irritating, are embedded on the cocoon itself, so they may act as a defensive device for the eggs themselves.
After egg laying, female dies, so the adult stage is very short, about two days and they do not feed. The eggs overwinter and the caterpillars will be born the following spring.
  There are several British species of a few moth families showing this pattern of female flightlessness, amongst them the Winter Moth. The limited mobility of the females is compensated by the highly dispersive larvae, which might be able to balloon when little. In the UK adults are found from July to September.
On this photo you can see the vestigial wing: just a small hairy flap (the head is down and the abdominal tip up, egg laying).
At 16:41 she had pretty much finished laying.
 I searched around for more cocoons nearby and found one under a wooden shelf by a large cotoneaster, about 2 m away from the first one. It looked very fresh and translucent, and still contained a caterpillar.
The large oval cocoon and large caterpillar inside points to another female will emerge from this one too.