Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

The Perfect Predator

Tuesday, August 11, 2009

What image does these words bring to mind? To some, it is a pride of lions hunting the plains of the Serengeti; others might think of a shark prowling the coastal waters; or a crocodile lying in wait at the rivers edge.

In fact, the perfect predator lives right here in my backyard. It is the spider; or rather, spiders as a group. There is no place more dangerous for a small prey animal than my back yard. Death lurks in every bush and bramble, every crack and crevice, every blade of grass. Death can strike from any direction, any time of night or day. Death is the concern of every small creature that inhabits my back yard, a death that I am totally unaware of unless I make a special effort to seek it out.

One summer night I went looking for Death.. With flashlight and magnifying glass in hand, I went hunting for the perfect predator.

It took a few minutes for my sensory awareness to diminish to the scale necessary, but before long, I started to see the predators. Two days earlier, I had seen a large moth wrapped in silk, attached to a bush, so I knew where to begin my search. In the glare of the flashlight, I found a large orb weaving spider perched in the center of a 15 inch web. The moth was now gone, sucked dry and discarded. In its place was an assassin bug, as large as the spider and just as deadly. Its days of terrorizing the neighborhood were clearly over. It too was shrouded in silk, waiting for the spider to regain her appetite.
Orb weaver spider imageOrb webs are the most easily recognized webs. These webs contain many straight lines of silk, radiating out from the central hub. Overlaying these straight threads is a line of sticky thread, spiraling outwards from the center. It is this sticky spiral thread that captures the prey. Some of the webs can get to be two to three feet in diameter with the spiders reaching about two inches from leg tip to leg tip. Most orb webs are much smaller with the web spanning a distance of two inches and the spider being not much larger than the period at the end of this sentence. Either way, both webs spell death for some unfortunate small creature. Every good-sized tree might easily contain a few of the larger spiders and thousands of the small ones.
Not all orb webs contain sticky threads. One group of orb weavers uses a very very fine thread, so fine that an insect will easily become entangled in it. These webs can be identified by the slightly bluish color of the silk.

The insects living in my back yard must worry about more than just orb webs. Sheet webs are just as dangerous. The sheet web consists of a single layer of non-sticky silk with a jumble of aerial lines above it. Any insect flying into the aerial lines falls onto the sheet. The spider, waiting under the sheet, bites the insect through the sheet and pulls it below where it can feed in relative safety.
Many of these sheetwebs can be found at the base of trees or under rocks or fallen logs. In some instances, the sheets are no longer flat, but stretched into a curved shape. The “Dome Spider” and the “Bowl and Doily Spider” are two very common spiders that spin their webs on low bushes and tall grass. The name of the spider I very suggestive of the shape of the web. An early morning walk with the dew showing off the webs will reveal one every foot or two across a large field.

Funnel Web Spider imageShould an insect try to travel under these webs, it must contend with the funnel web spiders. These spiders build their webs in the grass. The webs are flat sheets of non-sticky silk with a tube or funnel at one corner of the web leading to a hiding place. When an insect steps onto the web, the spider races across the web, bites the insect and drags it back into the funnel to eat it.

While many spider webs are beautifully designed, the cobweb spiders seem to have no discernible pattern to their webs. But many insects soon learn that they are just as efficient and deadly as any other web. Look for cobwebs in rock walls, brush piles or under the eaves of buildings. If you find one, chances are you will find a wrapped insect in the web as well as the spider.

If an insect manages to evade all webs (it is a tribute to the sheer numbers of insect that many do) it must still run a gauntlet of spiders. Coursing over the leaves of the trees and bushes are the jumping spiders ready to pounce on anything that moves. Down below patrolling the ground between the funnel webs are the wolf spiders. Both of these spiders actively chase down their prey. With their large eyes, they can often be spotted in the beam of a flashlight - the eyes glow like a cat caught in a set of headlights.Nursery Web Spider image
Other spiders are content to wait for the prey to come to them. A close inspection of flowers will reveal the crab spiders. Mostly daytime feeders, these spiders will sit motionless in the flower until some unsuspecting honeybee or other nectar feeder should wander too close. Oftentimes, a bee sitting unnaturally still in a flower indicates the presence of a crab spider.
Still other spiders might jump out of a hole in the ground, or dive through the surface of the water, or even throw their web at a passing insect. You might even find the spider that catches its prey by spitting at it.

Spiders have left no stone unturned in their search for food. They are the perfect predator. Which must mean that insects are the perfect prey. And I am content to be the perfect observer.