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Arthropods

Harvestmen Harvesting

9-15-17 daddy longlegs2 049A3934Like their relatives – spiders, mites, ticks and scorpions – Daddy Longlegs, or Harvestmen, have eight legs (the second, longer, pair of legs are used as antennae). Of all the arachnids, spiders resemble Harvestmen most closely.  However, there are distinct differences between the two orders. Unlike spiders, the two main body sections of Harvestmen are nearly joined and appear as one structure. Harvestmen have no spinnerets nor do they possess poison glands. They also do not have the enzymes spiders have that are capable of breaking down the insides of their prey into liquid. Harvestmen ingest small particles, breaking them down with their chelicerae, or mouthparts, which resemble miniature, toothed lobster claws. One would surmise from this photograph that the legs of flies must lack the nutrition worthy of mastication.

 

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Crustacean Deduction

9-18-17 crustacean 049A5188Arthropods are invertebrates possessing an exoskeleton, a segmented body and paired jointed legs. Crustaceans make up one group of arthropods. Insects, spiders, ticks, mites, crabs, lobsters, woodlice, centipedes and millipedes are all crustaceans. Underneath a rotting log I recently discovered a crustacean resting right next to a clump of eggs. Not wanting to disturb the creature, I hazarded a guess as to its identity from what I could see. Its form narrowed it down to either a woodlouse (also known as sow bug, pill bug and roly-poly), centipede or millipede. Most centipedes have one pair of legs per body segment, eliminating them from the field of possibilities, for the photographed crustacean has two legs per body segment, as do millipedes and woodlice.

The next clue had to do with the eggs, which I presumed were produced by the creature right next to them. Woodlice have a “marsupium,” a chamber under the thorax which is filled with water in which their (often several hundred) eggs are brooded. Millipedes, on the other hand, lay from ten to three hundred eggs at a time, and deposit them on moist soil. In some species an adult remains to guard the eggs.

I cannot categorically say that today’s subject is a millipede and its eggs, but all signs point to it. If there is a crustacean expert among Naturally Curious readers, please confirm or correct my deduced identification!


Grasshoppers Molting

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Molting is the process by which insects and other arthropods grow. They have an external skeleton (exoskeleton) that supports and protects their body, unlike the internal skeleton of most other animals. Since the exoskeleton is hard and its outer layer is non-living, it cannot grow bigger by small increments as the human skeleton does. As an insect increases in size, it sheds the inelastic exoskeleton on the outside of its body, and replaces it with a larger, soft exoskeleton that has formed underneath the smaller, shed exoskeleton. Eventually this new exoskeleton hardens. This process is repeated several times during the life span of an insect (the exact number depends on the species).

Grasshoppers experience incomplete metamorphosis: they go through three stages in their life cycle – egg, nymph and adult. Nymphs are miniature versions of adult grasshoppers, except that they are usually light in color and do not possess functioning wings. Nymphs undergo five or six molts and with each molt their size increases and their wing pads progressively develop. Usually within a month nymphs molt for a final time, emerging as adults with fully developed wings. (Photo: shed grasshopper nymphal skin showing small, developing wing pads; inset – fully mature grasshopper)


Millipedes Meandering

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How do you distinguish a millipede from a centipede – both multi-segmented arthropods that have a lot of legs? Although there are many less obvious differences, centipede bodies are relatively flexible and they have one pair of legs per body segment. Most of a millipede’s segments have two legs, and their tubular body is quite rigid.

Depending on the species, millipedes have between 80 and 750 legs, with most having fewer than 100, but they didn’t start out their lives with this way. When they hatch, millipedes only have three pairs of legs; every time they molt, they add more body segments and legs. When threatened, millipedes quickly coil their body into a spiral, protecting their legs and fragile underbody with their armor-like body plates (tergites).

If you come across a millipede, know that you’re looking at one of the earliest animals to breathe air and make the move from water to land. Pneumodesmus newmani, a fossil found in Scotland, dates back 428 million years and is the oldest fossil specimen with spiracles for breathing air.

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American Dog Ticks Can’t Give You Lyme Disease

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With the plethora of ticks this spring, it is perhaps comforting to know that not every tick you extract from your body has the potential to give you Lyme disease (or the powassan virus or many of the other diseases carried by Blacklegged Ticks (Ixodes scapularis), also known as Deer Ticks).

The American Dog Tick (Dermacentor variabilis) is the most commonly encountered tick in northern New England. It is found predominantly in areas with little or no tree cover, such as grassy fields and scrubland, as well as along walkways and trails. This species of tick feeds on a variety of hosts, ranging in size from mice to deer and humans. Despite the fact that the bacterium that causes Lyme disease has been found in American Dog Ticks, tests prove that the tick can’t transmit the organism to its hosts. Therefore, the American Dog Tick isn’t involved in the spread of Lyme disease. (It does transmit Rocky Mt. Spotted Fever, however, but there are relatively few cases of it in the Northeast.)

The UNH Extension Service has such a succinct description of this tick’s life cycle that I am sharing it here. It is a “three-host tick,” so named because it must find and feed on an animal three times to complete its two- year life cycle…The dog tick begins life as an egg, one of hundreds laid in a mass on the ground by a female tick. The egg hatches into a larva, which has six legs. The larva remains on the ground in leaf litter, or in low vegetation while waiting for a small mammal (usually a rodent) to brush by. It attaches to the animal and feeds for several days. Then it drops off and molts to the nymph stage, which has eight legs. Again it waits for a host (usually a rodent) to brush by. When that happens, the tick attaches and feeds on it for several days. When fully fed it drops off and molts to the adult stage. Adult ticks wait on shrubs or tall grass and attach to larger mammals such as people, deer, or pets. They also take several days to fully engorge (feed). A female fully engorged with a blood meal can be almost the size of a dime, appearing smooth and shiny. Mating takes place on the host, and when fully fed, the females drop off and lay eggs. The life cycle can be as short as three months. (Photo: American Dog Tick, Dermacentor variabilis)

CDC TICK PREVENTION TIPS:

Use repellents that contain 20% or more DEET (N, N-diethyl-m-toluamide) on exposed skin.

Use products that contain permethrin on clothing. Treat clothing and gear, including boots, pants, socks and tents.

Bathe or shower as soon as possible after coming indoors to wash off and more easily find ticks that are crawling on you.

Check yourself, your kids, and your pets for ticks daily, especially after they spend time outdoors in areas where ticks may be found.

Remove attached ticks as soon as possible. The preferred method of removal is to grasp the tick close to the skin with tweezers or fine-tipped forceps and gently pull upward with constant pressure.

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Grasshopper Wings Growing

7-21-16  grasshopper wings 092Grasshoppers experience incomplete metamorphosis, with three life cycle stages – egg, nymph, and adult.  A grasshopper egg hatches into a nymph, which resembles an adult grasshopper, except that it is smaller and lacks wings and reproductive organs.  Because of its hard outer exoskeleton, a growing grasshopper has to shed its skin periodically to accommodate its increased size.  (A larger exoskeleton develops beneath the old, smaller one that is shed.) Grasshopper nymphs molt several times (each stage between molts is referred to as an instar) before they reach their adult size, and with each molt, their “wing buds” get larger.  After the final molt, the wings are inflated and become fully functional.  Wings play an important part in grasshopper courtship, as males “sing” to attract females by rapidly rasping their leg against their forewing, a process called stridulation.

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Darners Laying Eggs

9-1-15 dragonfly laying egg 135Females of different species of dragonfly have different techniques for laying their eggs. Most skimmers, cruisers and clubtails dip the tip of their abdomen to the surface of the water while hovering or flying, and release their eggs. Most darners, such as the Shadow Darner (Aeshna umbrosa) pictured, have a sharp-edged ovipositor with which they slit open a stem or leaf of a plant on or near the water. They then push their egg into the plant tissue exposed by the slit. Because they are stationary during this process, female darners are vulnerable to predation by fish and frogs at this time. A close look at the bottom third of cattail leaves this time of year will tell you whether or not darners are in the vicinity, as the slits they make are very apparent, appearing as thin, tan, 1/2″ vertical lines.

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