Net-casting spiders are amazing arachnids that use their webs as projectiles to capture prey. Insects passing underneath never notice the Ogre-faced Spider hanging upside down above them. With incredible accuracy, the web formed into a net is thrown down and stretches out and around the insect, rendering it helpless.
Net-casting spiders: Identification.
Net-casting spiders (Deinopis) look more like sticks than spiders. Indeed, a net-casting spider in the ready position while hunting often only appears to have four legs.
Another distinguishing feature of net-casting spiders is their large forward-facing eyes. Two of these eyes are so big it results in an Ogre-faced appearance. Though the net-casting spider has no tapetum lucidum membrane like the wolf spider, it has better night vision than cats, dogs, or even owls.
Net-casting spiders have eyes 2,000 times more sensitive to light than humans.
The female net-casting spider can be as large as 1 inch in body length. Their color ranges from light chocolate brown to pinkish brown or fawn. Males have shorter, slenderer abdomens but longer legs. Males have darker colored and light gray lines running along their stomachs. There are gray “V” shapes on the head over the eyes on the male’s thorax.
spiders” class=”wp-image-11468″/>How net-casting spiders catch their prey.
As was noted above, net-casting spiders have a unique way of capturing and holding their prey.
First, they spin a blueish-white, small rectangular web using their cribellum, not spinnerets like other spiders. Cribellum consists of plates covered in thousands of sprayers. These sprayers produce fine silk with a wool texture that, while tiny, is incredibly strong.
It takes 30 minutes for a net-casting spider to create a catch web.
Next, the rectangular web is removed from its supporting threads and held directly over the ground by the net-casting spider’s two pairs of legs. Then, with its back legs and spinners attached to supporting lines, the spider waits, head down. The spider has placed a target of fecal matter directly beneath it as an aiming point.
Finally, when an ant or other insect passes under and into the target area, the net-casting spider drops the net over it. This net now stretches and entangles the insect, and the net-casting spider races down, bites, and envenoms it—rendering it paralyzed until it is consumed.
“Throughout each night of foraging, spiders hang motionless in their frame and typically remain in the same general location for more than a week.“
Unused nets may be stored for future use or eaten by net-casting spiders. Flying insects that come within range are also captured by net-casting spiders.
How a net-casting spider detects and captures flying insects.
According to Ogre-Faced, Net-Casting Spiders Use Auditory Cues to Detect Airborne Prey:
“Spiders do not possess insect-like “ears,” as no arachnid has been found to have a tympanal membrane. Even so, several spider species have been reported to detect airborne acoustic stimuli, beyond near-field range airflow, using non-tympanal hearing organs to accomplish this task. We found that isolated legs respond to acoustic stimuli; therefore, Deinopis legs must possess sensory organ(s) capable of auditory sensation.”
Figure 1. The Backward Strike Behavior of Deinopis Spiders
(A) Photograph depicting the massive eyes of Deinopis spiders, used in detecting prey items walking beneath their web at night. When visually occluded, spiders remain able to capture flying insects, though unable to capture prey off the ground.
(B) Photograph of a Deinopis spider in foraging posture in its natural habitat. When hunting, spiders grasp a rectangular capture-net between their front four legs while looking down, face forward, at the substrate below.
(C) Diagram of a typical frame web and net-casting spider when in foraging posture. The spider is suspended in mid-air while grasping the frame web (with its back pairs of legs) and the capture-net (with its front pairs of legs).
(D) A time series of a backward strike, illustrated by overlaying still frames from a high-speed video recording (2,000 fps). This behavior is used to capture flying insects and has been previously hypothesized to be elicited via acoustic cues emitted by the flapping of insect wings. See Video S1 for high-speed video recording of a backward strike.
spiders” class=”wp-image-11460″/>Net-casting spiders: Distribution, habitat, and diet.
Net-casting spiders are found in tropical and subtropical regions throughout Africa, Australia, and the Americas, including Florida.
During the day, net-casting spiders rest in gardens, shrubs, bushland, trees, and other vegetation. They are active at night, but on warm days, they can often be found walking around on plants.
Net-casting spiders feed on small flying insects, crickets, ants, beetles, and other spiders.
Net-casting spiders: Mating and reproduction.
After maturing in the late summer, net-casting spiders mate and lay egg sacs to reproduce.
Male net-casting spiders use the chemical cues produced by sexually receptive females and visual signals to search for potential mates.
Upon finding a mate, the male inserts his sperm-soaked palps into the reproductive opening on the female’s abdomen. The fable net-casting spider will then produce eggs and store them in a brown egg sac with darker born spots. Next, she will hide her egg sacs inside thick vegetation about three feet above the ground, and the spiderlings will hatch in the spring.
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