Dimorphic Jumping Spider

Appearance

In the males there are two forms, a very rare phenomenon in zoology. These use different courting displays, and differ in appearance: the "tufted" morph has a black body and pedipalps, three black tufts across its "head", and pale legs; and the "gray" morph has black and white stripes all over its body and legs, orange palps, and no tufts. However, each form accounts for 50% of the adult males, and they are equally successful in mating. A female of "Maevia inclemens" is 6.5 to 8.0 millimetres long, while males are 4.75 to 6.50 millimetres long.

Like all jumping spiders, "M. inclemens" has excellent vision. The main eyes, in the front-and-center position, are large, and are more acute than those of a cat and about 10 times as acute as a dragonfly's. The remaining three pairs of eyes are along the sides of the head, and work as motion detectors. The eyes are used for hunting, for avoiding threats and for finding and wooing mates. Almost all jumping spiders are predators, mostly preying on insects, on other spiders, and on other arthropods.

The body of "M. inclemens" is only sparsely covered with hairs and scales. A female of "Maevia inclemens" is 6.5 to 8.0 millimetres long, her carapace is light brown, her legs are pale and unmarked. The top of her abdomen is chalky or rusty colored, and along each side is a black band, often thinly covered with orange scales. Sometimes there is series of chevrons along the middle of her abdomen.

She has a prominent white stripe below the foremost eyes. There are spines on the first and second pair of her legs, but her body never has tufts of hair. Males are 4.75 to 6.50 millimetres long, and their carapaces are light to dark brown, with a black line around the edge. There usually is a pair of large lighter areas between the last pair of eyes halfway down the back of the carapace.

The eyes are surrounded by black. Males occur in two forms, a very rare phenomenon in zoology. The "tufted" morph has a totally black body, black pedipalps, white legs and three tufts of bristles on the front part of the cephalothorax. The "gray" male morph has a black and white striped body, a prominent white stripe on the foremost eyes, striped legs and bright orange pedipalps, and no tufts.

Jumping spiders have a distinctive rectangular carapace, and that of female "Maevia inclemens" average 2.30 millimetres wide, while the carapaces of males average 2.10 millimetres. The carapace of "M. inclemens" is fairly high, between 60% and 70% of the width.

Naming

"M. inclemens" is one of the 11 species in genus "Maevia". The species was first called "Attus inclemens", and other names have been used. The two male forms look and behave so differently that they were originally considered two distinct species. In 1955 Robert Barnes chose "M. inclemens", and this has become the standard name.

Distribution

"Maevia inclemens" is found throughout the eastern and mid-west United States and south-west Canada, including: Massachusetts, Connecticut, New York state, New Jersey, Pennsylvania, Maryland, West Virginia, Virginia, North Carolina, Florida, Alabama, Louisiana, Texas, Kansas, Kentucky, Indiana, Illinois, Michigan, Wisconsin, Quebec and Manitoba.

Reproduction

Each morph accounts for 50% of the adult males, and they make the same number of attempts to court females, but using a different courting display. Before looking for a mate, a male spider spins a small, flat web on a surface and ejaculates into it. He then loads the semen into syringe-like receptacles in both palps, and then searches for a female.

After sighting a female, the tufted morph pushes himself as high as possible with the last three pair of legs, and claps with the foremost pair, while at the same time waving the palps up and down, and swinging the abdomen from side to side, usually about 9 centimetres from the female. In contrast, the gray morph crouches down and points the foremost two pairs of legs directly forward, crosses the tips of the legs creating a triangle-like configuration, holds his orange-colored palps beneath his forward eyes, and glides back and forth in stationary or receding semi-circles in front of the female, at 3 centimetres away. The movements of the two morphs are identical later in the sequence.

When receptive, females respond similarly to both male types: approach and settle; extend the foremost pair of legs or tap with them. Both male morphs typically end their initial display and start leg-clapping and zig-zag dancing.

When tufted males clap, females look towards them and display a greater number of tap displays to them than to the gray morph. Females also respond to tufted morphs' clapping more often by settling than for gray males. However, after the females look towards the males, gray males approach the female more often than the tufted male. Females often tip their abdomens from side to side.

Finally the male mounts and copulates with the female. Afterward, the male generally dismounts and the two pair usually run away from each other. However, the male sometimes chases the female and tries to copulate again.

Food

Almost all jumping spiders are predators, mostly preying on insects, on other spiders, and on other arthropods. The most common procedure is sighting the prey, stalking, fastening a silk safety line to the surface, using the two pairs of back legs to jump on the victim, and finally biting the prey. Most jumping spiders walk throughout the day, so that they maximize their chances of a catch.