Bug of the Week

Funnel Web Spiders (Family Agelenidae)

Greetings, BugFans,

If you Google “funnel web spider,” the initial hits will be about Australian funnel web spiders, many of which are exceedingly venomous (especially Atrax robustus, who you will want to avoid should you ever set foot in Sydney). The BugLady once read an author who mused about why Australia, which lacks predators larger than a dingo (and most are much smaller), should have such an array of highly toxic snakes/spiders/octopi/etc. “Having 12 times the amount of venom required to kill a horse” is, by the BugLady’s reckoning at least, a pretty good definition of “highly toxic.” The good news, according to the excellent bugguide.net, is that the spiders that we in the U.S. call funnel-web spiders are in the family Agelenidae and are 99.9% harmless to people. The Aussie funnel web spiders are in a family of primitive spiders called Hexathelidae in the suborder Mygalomorphae. We’re familiar with Mygalomorphs because the big spiders we call tarantulas in the Americas are in the same suborder but are in the family Theraphosidae. These are more properly called bird spiders or hairy mygalomorphs. Hmmm – we’ve gotten into deep water pretty early in the game, here. The true (Old World) tarantula, whose toxic bite can only be counteracted by dancing a frenetic Italian dance that came to be known as the tarantell’a, is in the wolf spider family, Lycosidae. One of those instances of an old name getting recycled in a new country. There are about 600 species of FWSs worldwide, with half that number residing in North America. The Lesser European House Spider (Tegenaria domestica) is a naturalized American citizen whose ancestors probably arrived by boat from the Old World in the 1600’s. T. domestica is also called the cellar spider (not to be confused with the long-bodied cellar spider of previous BOTW fame). The webs of spiders in this genus emphasize the funnel, not the platform.

funnelwebspider
Funnel web spiders monitor the activity on their web from the safety of its funnel.

A male FWS lives to mate, and after mating, dies (please do not search for metaphors here). To woo his lady/ladies, he communicates by sound – vibrations called stridulations (noises made by friction, like grasshoppers and crickets) – and by touch – he strokes the female’s web seductively (again – no metaphors here). If the female allows him to occupy her web, they exchange bodily fluids. The lives of many females are restricted to their webs (still, no metaphors, but it’s getting harder…). If his life is devoted to the search for mates, hers is dedicated to being egg-ready, and to this end she concentrates on staying well-nourished. After mating, she creates a disc-shaped egg case and lays up to 200 eggs inside. Hiding her egg case in a crevice is her final act before she dies in fall, often with the egg case “in hand.” Her young hatch in spring, and they may disperse from their natal area on foot or by spinning tiny silken threads/”balloons” and taking to the air.

FWSs resemble wolf spiders. Both groups dress in shades/stripes of gray/brown; FWSs are slimmer than wolf spiders, with bodies no longer than an inch and with coarsely-bristled legs. Two spinnerets (silk-spinning organs) are prominent appendages at the end of their abdomen. One species of FWS may look and act pretty much like another species of FWS. FWSs are believed to have poor vision, despite their eight eyes that are usually arranged in two rows of four.

Wolf spiders don’t spin webs, but FWSs spin wonderful webs – flat, horizontal sheet webs with a tornado-shaped hole (funnel) leading down from the bottom layer and, if the web is located near shrubs, some guy-lines stretching up. Webs are generally spun on top of the grass (one group of FWSs is called “grass spiders”), but they can also be found in bushes and at the bases of woodpiles and buildings. Some over-achieving spiders make webs that are several feet across. Funnel webs are very tough, and if they are not disturbed they can last for months. Funnel webs are easily seen when they are covered with raindrops and look like a handful of diamonds tossed onto the grass. Recently, when the basswood flowers were falling, the FWS webs in the BugLady’s back yard were festooned with old flowers (it must drive the spiders crazy, running out to check each time a flower jolts the web).

There is some disagreement about the modus operandi of these commonly-observed spiders. MO #1: An unsuspecting insect mistakes the web for a handy landing strip, flies or hops onto the web’s top/barrier layer, and falls down to the next layer. MO #2: A flying insect hits the barrier web or the vertical lines that support some webs and drops onto the sheet below. MO# 3: The web is so intricately spun that unlucky insects that land there get their feet caught in the webbing. MO #4: Depending on the species of FWS, the web may or may not be sticky. If the web is not sticky (non-sticky webs are described as “dry and slippery”) the prey is caught when its feet become tangled in the web. Spiders that spin non-sticky-webs don’t know the trick of traversing sticky webs and may end up as prey if they wander across one. All of the MOs end with “and then the FWS rushes up from the bottom of its funnel and bites its prey” (FWSs are great sprinters that can appear/disappear in a flash). It takes only a few seconds for their venom to paralyze the prey, which is dragged back down the funnel so the spider can eat in peace. Insects make up most of its prey, but other spiders, even other FWSs, are fair game.

Like most spiders, FWSs do not bite unless they are provoked, and their bites are a minor inconvenience to all except the arachno-allergic. In her up-coming booklet, 101 Things You Can Do With Spider Webs, the BugLady will list the practice in Colonial times of putting the webs of Tegenaria spiders on wounds as a styptic. Also, webs of FWSs are filched by some species of birds to make a soft lining for their nests.

The Bug Lady