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Arachnids

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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Some Spiderlings Hatch in the Fall

antmiimic spider egg case 013Have you recently noticed a roundish, flat, papery, 1/4-inch diameter, metallic-looking structure adhering to the top of a rock? If it has tiny bumps in the center, chances are good that it’s a spider egg sac, most likely that of an antmimic spider (spiders resembling ants that often prey on ants), specifically one in the genus Castianeira. One would assume that the contents of the sac that were causing the bumps were eggs that were going to overwinter and hatch once warm weather arrives. This is true for a majority of spider egg sacs, but some, including those of Black-and-Yellow Argiopes and antmimic spiders, hold spiderlings that have already hatched and will remain in the sac throughout the winter. As long as the temperature stays cold, the spiderlings will be safe and secure until spring. If we have periods of cold interspersed with periods of warmer temperatures, or an exceptionally warm winter, the spiderlings will become active when the thermometer rises, and, not having any insects to eat, will be forced to devour each other.

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Spider Spinnerets

9-30-13 black and yellow sp. spinnerets2 IMG_4897Responses to yesterday’s Mystery Photo ranged from immediate deletion by a reader (due to the unappealing nature of the photo), to guesses including “bee butt,” “caterpillar mouthparts” and “deer tick.” Most responders, however, guessed correctly – the photograph was of the spinnerets of a Black-and-Yellow Garden Spider, Argiope aurantia.

Most spiders have six spinnerets — organs located on their abdomens from which silk is extruded. The individual spinnerets move independently yet in a highly coordinated manner. Each spinneret is dotted with many tiny spigots, through which various types and thicknesses of silk are extruded. The strong muscles that move the spinnerets also force liquid silk through the narrow spigots. This pressure, as well as external pulling by the spider, rearranges the liquid silk molecules into a solid but flexible thread. Although spider web silk is only about one millionth of an inch thick, weight for weight, it is stronger than steel (but not as strong as Kevlar). Unlike in the Mystery Photo, the spinnerets in this photograph are extruded and in use.

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Nursery Web Spiders Hatching

8-27-13 nursery web spider 169Nursery Web Spiders look a lot like Wolf Spiders, and the females of both families carry their respective egg sacs around with them until they hatch, but they do so in a different manner. Wolf Spiders grasp their egg sacs with the spinnerets (silk nozzles) located under their abdomen, whereas Nursery Web Spiders carry their egg sacs with their mouthparts. When hatching is imminent, the female Nursery Web Spider lashes leaves together with silk to form a protective shelter, or “nursery web,” for her egg sac and hatching offspring. The mother stands guard over her spiderlings, aggressively defending her young until they have had their first molt, after which both the spiderlings and the adult female disperse.

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Harvestmen

8-1-13 daddylonglegs 148Harvestmen (daddy longlegs) and spiders are closely related and share many characteristics, but they also have significant differences. One such difference is that Harvestmen do not possess venom glands, nor the digestive enzymes capable of breaking down the insides of prey into a liquid. (Some species of Harvestmen are omnivores, eating both plant and animal matter, others are scavengers.) Unlike fellow arachnids (spiders, ticks, scorpions and mites) that drink their food, Harvestmen ingest small particles, breaking them down with their chelicerae, or mouthparts, which resemble miniature, toothed lobster claws. In this photograph, the Harvestman is holding a deer fly with its pedipalps, appendages used to grasp food as well as their mates. Its chelicerae are too small to discern, but they do the job — in the space of about ten minutes, this Harvestman consumed an entire deer fly, bit by bit.

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