Amazing Spiders

For male Habronattus pyrrithrix spiders, the best way to attract a mate is by doing an elaborate, tail-shaking dance. The spiders wave their legs and shimmy their backsides, showing off their brilliant colors, which include rainbow markings on their bodies and a bright-red face.

The spiders have light-detecting photoreceptor cells in their eyes that allow them to see a range of colors. They can even see some things that are invisible to humans—like high-energy ultraviolet (UV) rays of light. However, the spiders don’t have cells that detect the color red. That puzzled scientists. Why would males have red faces if females couldn’t even see the markings?

To solve the mystery, Daniel Zurek closely examined the eyes of H. pyrrithrix spiders under a high-powered microscope. Zurek is a neuroscientist (brain scientist) who conducted his research at the University of Cincinnati, in Ohio. He located a tiny red spot on the spiders’ retina, a structure that lines the back of the eye. The red spot sits on top of photoreceptor cells and acts as a filter that allows the spider to identify red objects. “It’s as if you were wearing regular glasses with a red spot on the lens, so when you look through that spot you’d receive only red light,” explains Zurek.

Male Habronattus pyrrithrix spiders do a complex, tail-shaking dance. For them, it’s the best way to attract a mate. The spiders wave their legs and shake their backsides. This shows off their bright colors, including rainbow body markings and a bright-red face.

The spiders have cells in their eyes called photoreceptors. These cells detect light and allow them to see different colors. They can even see some things that humans can’t, like high-energy ultraviolet light rays. But the spiders don’t have cells that detect the color red. That puzzled scientists. Why would males have red faces if females couldn’t see the markings?

Daniel Zurek tried to solve the mystery. He closely studied the eyes of H. pyrrithrix spiders under a high-powered microscope. Zurek is a neuroscientist (brain scientist) who did his research at the University of Cincinnati, in Ohio. He looked at the spiders’ retina, which lines the back of the eye. There he found a tiny red spot. This spot sits on top of photoreceptor cells. It acts as a filter that allows the spider to detect red objects. “It’s as if you were wearing regular glasses with a red spot on the lens, so when you look through that spot you’d receive only red light,” explains Zurek.

Spiders of the genus Cyclosa are only a few millimeters wide, so some have developed a clever trick to keep larger predators away. The tiny critters decorate their webs with huge decoys that resemble spiders up to 10 times bigger than themselves. Cyclosa build their sculptures out of debris, like pieces of leaves that fall into their webs and the remains of insects they’ve eaten.

Scientists have long known that most Cyclosa spiders heap trash in their webs. The piles of junk could act as camouflage, where the spiders can conceal themselves from predators. But only two species of Cyclosa spiders are known to arrange debris into spider-shaped decoys, says Lary Reeves, a biologist who studies insects and spiders at the University of Florida. He discovered one of the species in the Philippines. The other lives in Peru.

Reeves believes the spiders developed their decoy-making abilities to ward off damselfly attacks. These insects, which look like dragonflies, like to eat tiny spiders but will stay away from larger ones. Long ago, Cyclosa spiders that happened to pile their trash into a big spider shape were less likely to be eaten by damselflies. They survived to pass on their unique decoy-building adaptation to future generations.

Spiders of the genus Cyclosa are only a few millimeters wide. So some have developed a clever trick to keep larger predators away. The tiny animals place huge decoys on their webs. The decoys look like spiders up to 10 times bigger than themselves. Cyclosa build them out of trash, like pieces of leaves that fall into their webs. They also use the remains of their insect meals.

Most Cyclosa spiders pile trash in their webs. Scientists have known that for a long time. The junk could act as camouflage, where the spiders can hide from predators. But only two species of Cyclosa spiders are known to create spider-shaped decoys, says Lary Reeves. He’s a biologist who studies insects and spiders at the University of Florida. He discovered one of the species in the Philippines. The other lives in Peru.

How did the spiders start making the decoys? Reeves believes it was because of damselfly attacks. These insects look like dragonflies. They eat tiny spiders, but they’ll stay away from larger ones. Long ago, some Cyclosa spiders happened to pile their trash into a big spider shape. Damselflies were less likely to eat them, so these spiders survived. They passed on their unusual decoy-making trick to future generations.

Unlike most spiders, triangle weavers don’t use venom to subdue their prey. Instead, they use their web to catapult themselves and to ensnare insects.

Triangle weaver spiders, which belong to the genus Hyptiotes, get their name from the triangular webs they construct. The spiders are extremely tiny—only 5 millimeters (0.2 inches) long. That’s about the diameter of a pencil-top eraser. Their small size makes them hard to find, says Daniel Maksuta, a physicist from the University of Akron, in Ohio, who studies the spiders. “To spot them, we look for webs constructed between V-shaped branches.”

Most spiders use venom to overcome their prey. But not triangle weavers. Instead, they use their web to launch themselves and their web. That way, they catch insects from far off.

Triangle weaver spiders belong to the genus Hyptiotes. They get their name from the shape of their webs. The spiders are extremely tiny. They’re only 5 millimeters (0.2 inches) long. A pencil-top eraser is about that wide. Their small size makes them hard to find, says Daniel Maksuta. He’s a physicist from the University of Akron, in Ohio, and he studies the spiders. “To spot them, we look for webs constructed between V-shaped branches.”

The Hyptiotes spider weaves its triangular web from one arm of a branch and attaches it via an anchor line to the other. The spider then cuts the line, but holds on to the two strands with its front and back legs. It’s body acts like a bridge, says Maksuta. The spider walks backward along the anchor line, pulling the web with it. Stretching creates tension that stores potential energy in the web.

Then the spider waits—sometimes for hours—for an insect to land in the web. As soon as one does, Hyptiotes releases its hold of the anchor line. That, in turn, releases the tension in the web, converting its stored potential energy into kinetic energy of motion. The web rockets forward with the spider in tow, entangling the insect. The spider wraps the trapped insect in more silk, sprays digestive fluids onto its prey, and chows down.

The Hyptiotes spider weaves its three-sided web from one arm of a branch. It attaches the web with an anchor line to the other. Then the spider cuts the line. But it holds on to both ends with its front and back legs. Its body acts like a bridge, says Maksuta. The spider walks backward along the anchor line and pulls the web with it. It stretches the web to create tension. This stores potential energy in the web.

Then the spider waits, sometimes for hours. When an insect lands in the web, Hyptiotes lets go of the anchor line. That releases the tension in the web. Its stored potential energy is converted into kinetic energy of motion. The web rockets forward with the spider in tow and traps the insect. The spider wraps the insect in more silk and sprays digestive fluids onto its prey. Then the hunter chows down.

Spiders don’t have wings, but some of them are still accomplished fliers. They take to the air by releasing thin strands of silk from organs called spinnerets in their abdomen. Scientists have long believed that the strands catch gusts of wind like a kite would, lifting the spiders skyward.

Spiders use this process, called ballooning, to travel long distances—sometimes hundreds of miles. Launching themselves into the air, not knowing where they’ll land, seems risky, says Erica Morley. Morley is a biophysicist—a scientist who applies physics principles to biological phenomena—at the University of Bristol, in the United Kingdom. “But there are lots of reasons why animals disperse,” adds Morley. The adaptation might serve as a way for spiders to spread out to reduce competition for food or to escape poor living conditions.

Spiders don’t have wings, but some of them are still good fliers. They use thin strands of silk to become airborne. This silk comes from organs called spinnerets in their abdomen. Scientists have long believed that the strands work like a kite does. They catch the wind and lift the spiders upward.

This process is called ballooning. Spiders use it to travel far, sometimes hundreds of miles. They launch themselves into the air, not knowing where they’ll land. That seems risky, says Erica Morley, a biophysicist at the University of Bristol in the United Kingdom. She’s a scientist who applies physics principles to biology problems. “But there are lots of reasons why animals disperse,” adds Morley. Ballooning might help spiders spread out, so they’ll have to compete less for food. Or it might be a way to escape poor living conditions.

A steady breeze, though, isn’t always necessary for spiders to balloon. Some scientists noticed that the animals could lift off on calm days too. Researchers wondered if something other than wind was helping spiders become airborne. Spider silk is negatively charged, while the atmosphere is usually positively charged. Could the attraction between the negatively charged silk and positively charged atmosphere create an electrostatic force strong enough to lift a spider skyward?

To find out, Morley placed a tiny spider known for ballooning in a box that shut out airflow. The box produced an electric field Morley could control. When she turned on the field, the spider released silk and ballooned to the top of the box. When she turned off the charge, the spider immediately fell. Morley’s findings proved that spiders can balloon using electrostatic forces alone. However, says Morley, spiders in the wild likely use a combination of electrostatic forces and air currents to stay aloft.

Spiders don’t always need a steady breeze to balloon. Some scientists noticed that the animals could lift off on calm days too. Researchers wondered if something besides wind was helping spiders become airborne. Spider silk is negatively charged, and the atmosphere is usually positively charged. The negatively charged silk and positively charged atmosphere attract one another. This creates an electrostatic force. Could it be strong enough to lift a spider upward?

To find out, Morley took a tiny spider that balloons. She placed it in a box with no airflow. The box produced an electric field that Morley could control. When she turned on the field, the spider released silk. It ballooned to the top of the box. When she turned off the charge, the spider fell suddenly. Morley proved that spiders can balloon using only electrostatic forces. But, says Morley, spiders in the wild likely use both electrostatic forces and wind to stay in the air.