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Arthropods

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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Hover Fly Mimics Bald-faced Hornet

8-5-15 bald-faced hornet and hover flyAdult hover flies, often referred to as syrphid (family Syrphidae) or flower flies, feed on pollen and nectar, and are often seen hovering at or crawling on flowers. Many have black and yellow bands on their abdomen, and are frequently mistaken for bees. There are certain species of hover flies that mimic stinging wasps, including yellow jackets and bald-faced hornets (see photo). Predators such as birds, ambush bugs, and spiders might think twice about eating an insect that can sting, and hover flies take advantage of this. The process through which this occurs is called Batesian mimicry, and refers to when a harmless species evolves to imitate a harmful species that has the some of the same predators.

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Snowfleas Appearing

snowfleas 049A7533One rarely even thinks about snowfleas (a species of springtail, Hypogastrura nivicola) until snow falls and then starts to melt. This is when these tiny wingless arthropods that catapult themselves through the air with the aid of a fork-like structure, or furcular, seem to magically appear out of nowhere. They actually are present year round, but their dark color makes them visible against the white snow.

The great majority of snowfleas live in soil, feeding on fungi, algae, decaying plant matter and bacteria. They work their way to the surface of the snow, crawling up the trunks of trees, plant stems and side of rocks where an open channel allows their migration. Thousands can be found on melting snow, especially in tracks or other depressions. No-one is absolutely sure of why they exhibit this behavior, though some scientists feel that these migrations are triggered by overcrowding and lack of food. Eventually those that survive on top of the snow make a return trip down into the soil.

Formerly classified as insects, snowfleas are now categorized as hexapods, due to some features they have which insects do not.

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Millipedes Migrating

11-11-14 millipede IMG_8982We don’t often see millipedes because of their preference for secluded, moist sites where they feed on decaying vegetation and other organic matter. Compost piles, heavily mulched shrub or flower beds, rotting logs, or the soil under logs and stones are likely spots to find these arthropods. Millipedes overwinter as adults, and have been seen migrating in the fall, presumably in search of overwintering sites that will provide them with some protection.

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Crickets Courting, Mating & Laying Eggs

10-10-14 cricket  003In late summer and autumn, crickets court by rubbing their forewings together, a practice referred to as stridulation. At the base of each forewing is a specialized vein with a series of hard “teeth,” or ridges – the “stridulatory file.” Only one is fully functional, and in crickets, it is usually the one on the left wing. On the inner, lower edge of the right forewing is the “scraper,” a sharp, hard projection that rubs against the file when the cricket opens and closes its wings during stridulation. In most species,it is the male crickets that “sing,” but both sexes have “ears,” or tympana, on their front legs. After mating, the female cricket deposits her eggs in the soil or in plant tissue, depending on the species. (Photo: female field cricket- note long ovipositor at tip of abdomen between the two sensory organs called cerci, which is lacking in male crickets)

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Black Widow Spiders

9-29-14 northern black widow spiderBlack widow spiders have been found in every state. They are a lot less numerous in New England than further south — their abundance is inversely related to the latitude — however, the northern black widow, Latrodectus mactans, (pictured) is here. According to Dr. William Spear, a noted arachnologist and provider of the information in this post, a black widow in northern New England would need a very sheltered site, such as the south-facing walls of buildings, south-facing sides of ditches, or perhaps even in barns and sheds, in order to survive.

The web of the northern black widow is a rather small (for the size of the spider) messy tangle, usually constructed close to the ground. The spider is generally not found on the web, but in a silk-lined pocket to one side and above the web. The silk of widow spider webs is unusually tough, and with experience one can learn to differentiate it from other spiders’ silk just by testing the web with a stick or pencil.

If knowing that black widows cohabit your state causes some discomfort, rest assured. Their bites are very rare and almost never fatal. The few fatalities that have been recorded are generally from children or persons weighing less than 100 pounds, or with precarious health. (Photo taken by Evan Kay in North Pomfret, Vermont in September, 2014; submitted by Caroline Robbins)

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Earwigs Mating

earwig2 -horizontal175Earwigs are elusive insects, primarily because they are nocturnal and during the day tend to hide in crevices. When we do see them, the first thing often noticed is their cerci, the pair of forceps-like pincers at the tip of their abdomen. These pincers are used primarily to capture prey (earwigs are scavengers for the most part, but some are omnivorous and prey on other insects) and for copulation. Male earwigs have curved pincers, while females have straight ones. After mating in the fall, the male and female earwigs spend much of the winter together, tucked away in a crack or crevice. By the time spring arrives, the male has left and the female has laid her eggs (the sperm stays viable within her for several months), which hatch in about a week’s time. Earwigs are one of few insects that provide maternal care for their eggs and offspring. (Photo is of male earwig eating the outermost tissue of a milkweed pod.)

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