Hover Flies, such as the this one above, look at the world in quite a different way than humans do. The structure and function of a flies eye are completely different from ours, and so they see shapes, motion and color differently. Flies are also able to see light in a way humans cannot.
Structure of a Compound Eye
Compound eyes are made up of thousands of individual visual receptors, called ommatidia. Each ommatidium is a functioning eye in itself, and thousands of them together create a broad field of vision for the fly. Each ommatidium is a long, thin structure, with the lens on the outer surface of the eye, tapering to a nerve at the eye’s base. When the ommatidium receives light, it is filtered through the lens, then a crystalline cone structure, pigment cells and visual cells. Every ommatidium has its own nerve fiber connecting to the optic nerve, which relays information to the flies brain.
Flies Can’t Focus
A human’s eye is attached to muscles that allow it to move, expanding the field of vision and making it possible for the eye to gather more information about its surroundings. Instead of moving their eyes, flies receive information from several different points simultaneously. A flies eyes are immobile, but because of their spherical shape and protrusion from the flies head they give the fly an almost 360-degree view of the world. In a human eye, the pupil controls how much light comes into it, which is focused by the lens onto the retina. The retina then relays information to the brain via the optic nerve. Because fly eyes have no pupils they cannot control how much light enters the eye. With no control over how much light passes through the lens, the fly cannot focus the image it sees. Flies are also short-sighted — a visible range of a few yards is considered good for an insect.
The Mosaic Effect
The best analogy to describe a flies vision is to compare it to a mosaic — thousands of tiny images convalesce, and together represent one visual image. Each one of these pictures represents information from the fly’s individual ommatidium. The effect is much like how we see stippling or newspaper print — up close the image is a lot of tiny dots, but take a step back and it’s a complete image. The more ommatidia a compound eye contains, the clearer the image it creates.
There’s a reason why flies are especially jumpy creatures that take off at the slightest flinch. A flies vision is nowhere near as clear or effective as a human’s, but it’s especially good at picking up form and movement. As an object moves across the fly’s field of view the ommatidia fire and stop firing. This is called a flicker effect. It’s similar to how a scrolling marquis works — with lights turning on and off to give the illusion of motion. Because a fly can easily see motion and form, but not necessarily what the large moving object is, they are quick to flee, even if the moving object is harmless.
Flies have limited color vision. Each color has its own wave frequency, but flies have only two kinds of color receptor cells. This means they have trouble distinguishing between colors, for instance discerning between yellow and white. Insects cannot see the color red, which is the lowest color frequency humans can see. However, houseflies have the ability to see polarized light, but humans cannot differentiate between polarized and unpolarized light. Polarized light is light in which the waves travel only in one plane.
Wolf Spiders are members of the family Lycosidae. They are so named because their method of hunting is to run down their prey like that of a wolf. Wolf Spiders are robust and agile hunters that rely on good eyesight to hunt, typically at night. Wolf Spiders resemble nursery web spiders (family Pisauridae), however, they carry their egg sacs by attaching them to their spinnerets (instead of by means of their jaws and pedipalps).
Wolf spider Characteristics
Wolf Spiders range from about half an inch to 2 inches in length. They are hairy and typically brown to grey in colour with a distinct Union Jack impression on their backs. The spiders undersides are light grey, cream or black, sometimes salmon pink.
Wolf Spiders have eight eyes arranged in three rows. The bottom row consists of four small eyes, the middle row has two very large eyes and the top row has two medium-sized eyes.
Wolf Spiders depend on their good eyesight to hunt. Their sense of touch is also acute. The sides of their jaws may have a small raised orange spot or ‘boss’.
Because they depend on camouflage for protection, Wolf Spiders do not have the flashy appearance of some other kinds of spiders. In general their colouration is appropriate to their favoured habitat.
Wolf Spiders eyes reflect light well and one way of finding them is to hunt at night using a flashlight strapped to ones forehead so that the light from the light is reflected from their eyes directly back toward its source.
Wolf spider Habitat and Webs
Wolf spiders can be found in a wide range of habitats both coastal and inland. These include shrub lands, woodland, wet coastal forest, alpine meadows and suburban gardens.
Wolf spiders are commonly known as household pests as when the weather starts getting colder, they look for warm places to overwinter in homes. Wolf Spiders are commonly found around doors, windows, house plants, basements, garages and in almost all terrestrial habitats. Wolf Spiders do not spin a web, instead, they roam at night to hunt for food. Wolf spiders are often confused with the Brown Recluse spider, however, they lack the violin-shaped marking of the Recluse. The wolf spider is shy and is most likely to run away when disturbed.
Wolf spider Diet
Two Wolf spider species are known to be predators of cane toads. Lycosa lapidosa will take small toads and frogs while Lycosa obscuroides has been noted biting and killing a large toad within one hour.
Wolf spider Reproduction
Mating takes place outside the females burrow at night. Some adult male Wolf spiders of smaller-sized species are known to disperse by air in order to find mates. The male is attracted by scent markings left by the female, often associated with her drag-line silk. Males perform a courtship ritual prior to mating, often involving complex leg and palp signaling to the female.
The female Wolf spider constructs an egg sac of white papery silk, shaped like a ball with an obvious circular seam, which she then carries around attached with strong silk to her spinnerets. When the spiderlings hatch, they are carried around on the females back until they are ready to disperse by ballooning or on the ground. Such a high degree of parental care is relatively unusual among spiders. Wolf spiders live for up to 2 years.
Wolf spider Venom
The Wolf Spider is not aggressive, however, it will inject venom freely if continually provoked. Symptoms of its venomous bite include swelling, mild pain and itching. Though usually considered harmless to humans, its bite may be painful.
Dolycoris baccarum Hairy Shieldbug
A large and distinctive purple-brown and greenish shieldbug which is covered with long hairs. The antennae and connexivum are banded black and white. During the winter, the ground colour becomes uniformly dull brown.
This bug overwinters as an adult, emerging in the spring. Larvae, which are also hairy, may be found on numerous plants, particularly those in the Roasaceae. The new generation is complete from August onwards.
Common and widepsread in many habitats throughout Britain, particularly hedgerows and woodland edges, becoming scarcer and mainly coastal in the north.
Adult: All year
Length 11-12 mm
Taken at Lunchtime today, this Spider was hiding in the hollow of a garden tree. I am not sure what kind of spider she is but am going through lots of websites and wildlife books I have.
At the moment I am keeping my Macro lens on my Camera all the time, I am missing taking some more general landscape images but truly enjoying spending sometime getting much closer to the nature that I find at home or very close to home. Macro photography is not easy and a true skill, so the more macro’s I find myself taking the more confident I am feeling in this area 🙂
The world we live in is full on the most amazing things, some of these things we see everyday around us in a very clear and detailed way, others we have to stop and take a little more time in order to observe. This is why when I get this time I love using a Macro Lens, you can get in close to the small things of life, getting a view that is hard to get from a distance.
This summer more than ever before I want to use my macro lens in order to record the small things in nature 🙂
A Gallery of images taken over the last four days here in county Kilkenny and Tipperary, Springtime has almost arrived 🙂 ….