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Sheet Web Weavers Still Active

10-9-15 sheet web IMG_5116Spider webs are constructed in a variety of shapes, for which many of them are named. Among others are orb webs, triangle webs, mesh webs and sheet webs. One of the most prevalent types of spider webs seen this late in the year is the sheet web, made by members of the Lynyphiidae family.

Several different web designs are found in this family including the bowl and doily, dome, and sheet. Tiny sheet web weavers spin small horizontal sheets of webbing and then hang upside-down underneath their web. Some species make two layers and hide between them for protection. When a small insect walks across the web, the spider bites through the silk, grabs its prey, pulls it through the web and eats (actually drinks) it.

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Spiderlings Dispersing

9-25 spiderlings dispersing 615Although many spider eggs hatch in the spring, there are some that hatch in the fall. Most spiderlings stay within the egg sac until they undergo their first molt – their small cast skins can be seen inside the old egg sac. After molting they emerge and cluster together, still living largely upon the remnants of yolk sac in their abdomens. In several days the spiderlings are ready to disperse, which is necessary to avoid competition for food and prevent cannibalism among the hungry siblings.

Some species, especially ground dwellers, disperse by walking, often over relatively short distances. Others, particularly foliage dwellers and many web builders, mainly disperse by ballooning. To balloon, spiderlings crawl to the top of a blade of grass, a twig or a branch, point their abdomens up in the air and release a strand of silk. Air currents catch the silk, often called gossamer, and lift the spider up and carry it off. Aerial dispersal may take a spiderling just a few feet away or much, much farther – spiderlings have been found as far as 990 miles from land. (Charles Darwin noted spiderlings landing on the rigging of the Beagle, 62 miles out to sea).

Spiders Molting Exoskeletons

shed spider skin 052Like other arthropods, spiders have a protective hard exoskeleton that is flexible enough for movement, but can’t expand like human skin. Thus, they have to shed, or molt, this exoskeleton periodically throughout their lives as they grow, and replace it with a new, larger exoskeleton. Molting occurs frequently when a spider is young, and some spiders may continue to molt throughout their life.

At the appropriate time, hormones tell the spider’s body to absorb some of the lower cuticle layer in the exoskeleton and begin secreting cuticle material to form the new exoskeleton. During the time that leads up to the molt (pre-molt period), a new, slightly larger, inner exoskeleton develops and is folded up under the existing exoskeleton. This new soft exoskeleton is separated from the existing one by a thin layer called the endocuticle. During the pre-molt period the spider secretes fluid that contains digestive enzymes between the new inner and old outer exoskeletons. This fluid digests the endocuticle that separates the two exoskeletons, making it easier for them to separate.

Once the endocuticle is completely digested the spider is ready to complete the molt. At this point a spider pumps hemolymph (spider blood) from its abdomen into its cephalothorax in order to split its carapace, or headpiece, open. The spider then slowly pulls itself out of the old exoskeleton through this opening.

Typically, the spider does most of its growing immediately after losing the old exoskeleton, while the new exoskeleton is highly flexible. The new exoskeleton is very soft, and until it hardens, the spider is particularly vulnerable to attack.

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Sac Spider Shelter Serves as Nursery & Coffin

7-10-15  sac spider 018It is not unusual to come across a rolled-up leaf – the larvae of many moths create shelters in this fashion, using silk as their thread. Less common, and more intricate, are the leaf “tents” of sac spiders. With great attention paid to the most minute details, a female sac spider bends a leaf (often a monocot, with parallel veins, as in photo) in two places and seals the edges (that come together perfectly) with silk. She then spins a silk lining for this tent, inside of which she lays her eggs. There she spends the rest of her life, guarding the eggs. She will die before the eggs hatch and her body will serve as her offspring’s first meal. (Thanks to Ginny Barlow for photo op.)

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Predator Eating Predator

fishing spider and dragonfly 385The Six-spotted Fishing Spider, Dolomedes triton, is an arachnid in the nursery web spider family Pisauridae. As its name implies, the Six-spotted Fishing Spider does occasionally eat small fish, but also consumes other invertebrates and tadpoles. The hunting techniques of fishing spiders are varied. Often they sit patiently during the day, waiting hours with their legs stretched out for an unsuspecting insect (such as the pictured Dot-tailed Whiteface dragonfly) to land on the same lily pad or leaf that the spider is sitting on. They can and do walk on water as well as dive up to seven inches deep in order to catch aquatic prey. The Six-spotted Fishing Spider in this photograph has removed the head of its prey and is drinking its liquefied innards.

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Spiders Hibernating

11-24-14  spider 050Spiders that don’t lay eggs and die in the fall have developed several adaptations to survive the cold temperatures and lack of food that winter presents. They seek out microhabitats for protection, increase their resistance to cold and reduce their metabolic rate.

About 85% of spiders that overwinter do so in leaf litter, where they are well insulated against the cold. Most of these spiders assume a rigid position, with their legs drawn close to their body so that the amount of exposed body surface is kept to a minimum. Leaf litter protects spiders from extreme temperature fluctuations and from desiccation. A heavy snow cover ensures a fairly steady temperature of 32° F. regardless of the air temperature, even in weather as extreme as -40 ° F. below zero.

Many of the remaining overwintering spiders can be found under the loose bark of dead trees. Some have no further protection, others, such as the pictured Eastern Parson Spider, spin a silk case within which they spend the winter.

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Funnel Weaving Spiders Spinning Last Webs of the Year

10-16-14 funnel weaver web 045A number of unrelated spider families in North America spin webs with funnel-shaped retreats. These spiders are all referred to as funnel weavers. The spider lies in wait in the funnel, and when an insect flies into or lands on the web, the spider rushes out, checks to see if it is prey, and if it is, bites it. Its venom is fast-acting, and as soon as the prey is largely immobile, the spider drags it back into its funnel to safely consume it out of sight. Many species’ funnel webs are horizontal, and found in grass and bushes, but others are vertical. Like most spiders, funnel weavers are nocturnal. Many species die in the fall, but a few live a year or two. If you find a funnel web inhabited, it is likely to be a female. Males spend most of their life wandering in search of a mate, and after finding one and mating a few times, often die.

Funnel weaving spiders are docile and non-aggressive, and their bite is rarely as bad as a bee sting. Funnel weaving spiders are sometimes referred to as “funnel web spiders.” True funnel web spiders are not found in North America, but in Australia, where their bite is considered harmful.

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