Being able to identify the webs of common spiders is essential for all pest managers.
Spider webs are one of the more amazing biomechanical evolutionary developments. Being able to identify spider webs (when the spider isn’t present) is a basic skill for pest managers. Here we dive a bit deeper into the webs of the common spiders found around homes.
How are they made?
Spider web silk is a remarkable material. Made almost entirely from large protein molecules, it is as strong as steel and as elastic as rubber, with antimicrobial activity and is completely biodegradable. There is no single type of silk; in fact, some spiders produce several different types of silk, which vary in strength and stickiness, depending on their use in the construction of the web. The silk is produced from the spinneret glands, with the different glands producing a different type of silk. Each gland is associated with a spinneret from which the silk is extruded (it is liquid inside the spider). The different spiders produce webs of different designs according to their requirements – primarily based on location and target prey.
Black house spider
The black house spider builds dense, funnel-shaped webs. Coupled with the colour of the spider, it is one of the reasons homeowners sometimes confuse black house spiders with funnel-web spiders. The web is made from cribellate silk, which is laid down in lacy silk sheets around the entrance to the spider’s retreat. These sheets aren’t sticky but are designed to snag the hairy legs of prey insects. Over time, as more layers are laid down, the webs can become very dense.
Black house spiders build their webs around their retreats, which is why they are typically found around doors and windows – anywhere where there is a crack or crevice to hide. If hiding places are lacking, they will also build their webs under the eaves. Removal of these webs is best achieved by brushing. Hosing can result in the web sticking to surfaces and being more difficult to remove.
Redback spider
Redback spider webs look like a messy fishing net and will often contain debris, such as dry leaves. Although apparently somewhat haphazard, the web does have some structure, with the rear portion of the web being somewhat denser and forming a funnel opening where the spider can hide. It’s classified as a gum-footed tangle web, which describes how it is used to catch prey. A series of vertical, sticky threads run from the web to the ground, to target crawling prey. When prey run into these strands, the cross strands holding them in place break, and the strand retracts from the ground, lifting the prey with it (main picture, above).
Redback spiders build their webs in dry sheltered spots – in cracks and crevices, under furniture, in weepholes and vents, and inside metal tubular fencing. The sticky catching lines will extend out into the open where they can catch passing prey. Sometimes the webs themselves are not particularly easy to see with only the catching lines extending from the hiding spot visible. It is important to spray into these hiding spots to ensure control.
Funnel-web spiders
Funnel-web spiders build burrows in moist, cool, sheltered areas. The spider lines the burrow with silk making a tunnel, but it’s the obvious silk trip lines that radiate out from the burrow that identify it as a funnel-web burrow. The webs of tree-dwelling funnel web spiders also have the obvious trip lines, although the spiders hide in cracks and crevices in the tree rather than burrows.
Sometime funnel-web burrows can be confused with trap door spider burrows, especially if it is a species without a trap door to the burrow. However, the trap door spider only uses silk to line its burrow and hinge the trap door – it lacks the obvious radiating trip lines of the funnel web.
Golden orb weaving spider/St Andrews cross spider
Both of these spiders produce the classic spider web – a spiral orb web. Hung in open spaces between trees and shrubs, they are designed and positioned to catch flying insects. If you have ever wondered how a spider manages to build the web across what sometimes appears to be impossible gaps, the success comes from the first strand of silk. The spider floats a line on the wind until it hits a surface on the other side of the gap. It then tightens the strand so it can traverse the gap, before strengthening this initial line and commencing construction of the web.
Main image photo credit: Calistemon, CC BY-SA 3.0
