An online resource based on the award-winning nature guide

Arachnids

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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Wolf Spider Eggs Hatching

6-10-14 wolf spider & egg sac & babies IMG_7251Female wolf spiders provide both their eggs and young with a considerable amount of maternal care. They actually carry their egg sac around with them, attached to the spinnerets at the end of their abdomen, as they hunt for food and go about their lives. Careful to keep her egg sac from touching the ground, the mother makes sure it receives a sufficient amount of sunlight each day, presumably to enhance incubation. She also mends any tears that appear in the sac. The eggs hatch in one to two weeks, and 4 to 22 days later, the mother perforates the egg sac either part way or all the way around the seam by rotating the sac with her legs as she makes tiny holes in it with her chelicerae (mouthparts). Within three hours of this, spiderlings crawl out of the sac through the holes made by the mother, climb up onto her abdomen (see photo), and remain there for days or weeks, depending on the species.

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Jumping Spider Guards Egg Sac

6-5-14 jumping spider2  077Spiders protect their eggs by wrapping them up in a sac they make out of silk. Some species (such as garden, or black-and-yellow argiope, spiders) then die, leaving their egg sac to withstand the elements, as well as potential parasites and predators, on their own. As you would guess, these sacs are usually fairly impenetrable. In other species, female spiders survive long enough to guard their eggs until they hatch, or even until the young spiderlings disperse, and these sacs are usually far less tough. In the species where the female protects her eggs, some females carry their egg sacs with them at all times (wolf spiders, nursery web spiders) while others (jumping spiders) simply remain with the sac. Their excellent eyesight and impressive ability to leap many times their body length gives jumping spiders an advantage over any potential predators. (Photo – jumping spider with egg sac)

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Cold Snaps & Hardy Invertebrates

1-14-14 TICK IMG_0528As you may have heard, there could be a plus side to the sub-zero temperatures we’re experiencing this winter – the cold weather may well decrease the number of invasive pests we have. For example, the Hemlock Woolly Adelgid (the aphid-like introduced insect decimating the Eastern Hemlock population) succumbs at 4 or 5 degrees F. However, other insects aren’t phased by the cold until it dips way below zero. At -20 F., roughly half of the Emerald Ash Borer larvae (an invasive beetle that is highly destructive to ash trees) overwintering in trees will die. Once the temperature reaches -30 F., there’s a 90 percent mortality rate. Bed bugs face instant death at -22 degrees F., but it takes 24 hours to kill them at -11 degrees F. and 72 hours to kill them at 0 degrees F. Unfortunately, once an invasive insect establishes itself, even if its numbers go way down for whatever reason, it usually rebounds in several years’ time. Some invertebrates are not affected by the cold temperatures. The Black-legged (Deer) Ticks that reside on moose, deer, mice, birds and other hosts can withstand sub-zero temperatures as they have the warmth of their hosts’ bodies to keep them warm. In order for ticks to succumb to the cold, the frigid air has to last until May, when the fertilized female ticks fall off their hosts to lay their eggs.

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