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Arthropods

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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Milkweed Tussock Moth Caterpillars Feeding

milkweed tussock moth2 038Female milkweed tussock moths lay their eggs in masses on the underside of milkweed and dogbane leaves, which their larvae will eat. The hatching caterpillars are gray and hairy, but in no time they have developed the tufts of hairs that give them their name and make them resemble little mops. When still fairly young, the siblings stay together, skeletonizing the leaves they consume, leaving only the strongest veins that contain sticky latex. As they mature, the caterpillars tend to wander, and it’s unusual to find large groups of them on a single leaf. At this point they often cut through a vein in order to prevent the latex from reaching the area of the leaf where they are feeding. (Older monarch caterpillars use this same tactic.) Like monarchs, milkweed tussock moths, because they’ve consumed the cardiac glycosides contained in milkweed and dogbane leaves, are toxic to predators.

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Antlions Trapping Insects

8-14-14  antlions - 230The larvae of a predaceous group of winged insects (family Myrmeleontidae) that closely resemble dragonflies and damselflies are referred to as “antlions” – they have the ferociousness of a lion and prey mainly on ants. The manner in which an antlion traps its prey is ingenious. It excavates a conical pit in sandy soil (an antlion is also called a “doodlebug” because of the squiggly trails it leaves in the sand looking for just the right spot for a pit). Using its head as a shovel, it tosses out sand as it turns in a circle, digging deeper and deeper, until it forms a pit roughly two inches deep and three inches wide. The antlion lies at the bottom of the pit, covered by a thin layer of sand except for it pincer-like mandibles, which are ready to snatch prey at a second’s notice.

The slope of the sides of the pit is at the angle of repose – as steep as it can be without giving way – so when an ant accidentally steps over the edge of the pit and falls in, the sand beneath it collapses, carrying the ant to the bottom of the pit and into the pincers of the waiting antlion. If the ant tries to scramble up and out of the pit, the antlion tosses a load of sand at the ant, knocking it back down. The antlion then injects venom and digestive fluids into the prey via grooves in its mandibles, and drinks the innards of the ant through these same grooves.

The antlion’s anatomy is as unusual as its method of capturing prey. It has a mouth cavity, but no mouth opening, and no external opening for solid waste. Because digestion takes place outside of its body, the antlion doesn’t accumulate a lot of waste, but what it does accumulate stays inside of it until the antlion matures into an adult. This can be anywhere from one to three years, depending on the species. When fully developed, the antlion constructs a small, round pupal case out of silk and sand, in which it overwinters. It emerges from this case the following spring as a winged adult. (Thanks to Joan Waltermire and John Douglas for photo op.)

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Carrion Beetles Feeding

7-30-14 carrion beetle feeding 129When an organism dies, such as the pictured American Toad, a series of decomposers appear and break it down. Some of the first insects to arrive at the scene are blowflies, and they lose no time in laying eggs which rapidly hatch into larvae, or maggots. A bit later, carrion beetles move in. Both of these insects live in dead carcasses, where they eat raw flesh and fungi. There is great competition, believe it or not, for rotting bodies, and carrion beetles such as the pictured American Carrion Beetle (Necrophila americana) have managed to find a way to eliminate some of it. They carry tiny mites on their backs which travel from carcass to carcass with the beetles, devouring the eggs of maggots as well as the smallest maggots themselves. In addition, carrion beetles secrete a strong offensive odor that irritates other insects and predators, a second effective way to reduce the number of insects competing for a corpse.

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Twelve-spotted Tiger Beetle Larva at Work

7-24-14 tiger beetle adult and larva 040Without doubt, I have one of the most erudite readerships in the land of blogs. Several people recognized this uncommon phenomenon. To clear up a few misconceptions, however, being a male, this dragonfly was not laying eggs. Neither was it fertilizing them – male dragonflies perform this act when coupled with a female. This Chalk-fronted Corporal had the misfortune to sun itself on a tiger beetle-inhabited patch of sand. One of the most aggressive groups of insect predators is the tiger beetle family. They are especially known for their speed – up to 5.6 mph, which is comparable to a human running 480 mph. If you watch an adult tiger beetle hunting, you’ll notice that it stops and starts frequently. This is because it runs so fast it goes blind — its brain has trouble processing the information it sees, and the beetle must stop to regain its sight.

The larvae of the Twelve-spotted Tiger Beetle live in tunnels that they dig in the sand (some of you noticed tiny holes near the dragonfly) that can be up to a foot deep. The larvae have hooks located on the back of their abdomen to anchor them to the side of the burrow. Tiger beetle larvae are also predators, and after digging a tunnel the Twelve-spotted Tiger Beetle will crawl up it until just the top of its head is visible. From this position the larva watches for prey wandering by. When it sees a potential meal, such as yesterday’s dragonfly, it flips backwards faster than you can blink an eye and grabs its prey, pulling it down as far as it can into its tunnel, where it safely feasts on its catch. The portion of the Chalk-fronted Corporal’s abdomen that was inside the tiger beetle tunnel was completely consumed except for the outer skeleton.

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