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Defense Mechanisms

Black Swallowtail Larvae Defending Themselves

7-8-19 black swallowtail larva 0U1A0103Caterpillars, the larval stage of moths and butterflies, are very susceptible to predators (escaping quickly is not an option). Much of their energy in this stage is devoted to defense mechanisms to thwart would-be predators. A partial list of these defenses includes irritating bristles with detachable tips (Tussock Moths), toxic “breath” (Tobacco Hornworms, consumers of tomato plants, tobacco and other plants in the nightshade family, release toxic, bad-smelling nicotine), toxic bodies (Monarchs) and anti-coagulant venom (Giant Silkworm Moths).

Black Swallowtail (Papilio polyxenes) larvae defense mechanism strategies change as they develop. In early stages, or instars, they mimic bird droppings (not an appealing meal for most predators) and older larvae possess bright yellow-orange, horn-like organs behind the head known as osmeteria (see photo inset). When threatened, larvae rear up, extrude the osmeterium, and attempt to smear potential predators with a chemical repellent.

Black Swallowtail larvae are frequently sought after by parasitoids, which can locate their hosts by chemicals in the hosts’ feces (frass). To decrease their chances of being parasitized, Black Swallowtail larvae toss their fecal pellets away from themselves with their mandibles.

To learn much more about both moth and butterfly larvae, go to http://www.thecaterpillarlab.org.

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Blister Beetles’ Defense Mechanism

10-5 short-winged blister beetle 064Blister beetles are aptly named, for when they are disturbed they emit a yellow, oily, defensive secretion (cantharidin) from their joints which usually causes blisters when it comes in contact with skin. This toxin deters many potential predators and is especially effective against ants. According to naturalist/forester/writer Ginny Barlow, as little as 100 milligrams is reported to be fatal to humans if ingested, and this amount can be extracted from just a few beetles. Humans used to crush and dry blister beetles and use the resulting concoction for gout and arthritis. It was also used as a popular aphrodisiac known as Spanish fly. Because of its toxicity, it is no longer widely used in medicine.

Cantharidin is, however, indirectly used by tree-nesting nuthatches. With a limited number of tree cavities, there is competition among animals using them to raise their young, especially between squirrels and nuthatches. Nuthatches have been seen with Short-winged Blister Beetles (Meloe angusticollis, see photo) in their beaks, “sweeping” them on the bark around tree cavity entrances. The nuthatches don’t eat the beetles, they strictly use them as tools. It is assumed that the birds do this in order to repel squirrels with the cantharidin that is smeared on the tree. (Thanks to Ginny Barlow for photo opportunity.)

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Two-month-old Striped Skunks Can Spray!

7-15-15 striped skunk2 058The answer to yesterday’s mystery photo is a lot less original than many of your guesses, all of which could have been true, given my natural curiosity. I am embarrassed to admit that it was the oily, yellow spray of a young striped skunk that covered my spectacles (and my entire head, arms and camera) – even with ample warning, I chose to persevere in order to get the perfect picture. Unfortunately, the skunk was a lot more successful at his mission than I was at mine.

There is a reason why coyotes, foxes and most predators (one exception is the great horned owl), including most sane photographers, keep their distance from striped skunks. Whether newborn or several years old, skunks are capable of using their musk-filled anal glands to ward off anything that threatens them. Skunks are generally reluctant to spray, however, as they only have a few teaspoons (half an ounce) of musk in their glands, and once their supply is depleted (five or six sprays), they are defenseless for about 10 days, while it builds up again. Hence, plenty of warning is given in the form of stomping front feet, erect hair, raised tail, and chattering before a skunk contracts the muscles surrounding its anal glands and shoots a pungent, yellowish spray as far as ten feet away. Only a fool would not heed the warning given…and be forewarned – a skunk’s aim is surprisingly accurate.

The organic compounds that make the smell of skunk spray so offensive are called thiols (mercaptans). Thiols are also found in garlic and onions, and form parts of the keratin in hair. If your dog or you happen to be at the wrong end of a skunk’s partially everted anus, the best combination to neutralize the musk smell is 1 quart of 3% hydrogen peroxide, ¼ cup of baking soda, and 1 teaspoon of liquid dish soap. (Thanks (?) to Tom Ripley for photo op.)

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Tortoise Beetle Larvae Making Fecal Shields

8-1-14  tortoise beetle larva with fecal shield 049Instead of discarding feces, or frass, some insects save their waste matter for defensive purposes such as “fecal shields.” These are coverings over the back of the larvae that are made largely of feces and provide either physical or chemical barriers to predation. Adult Tortoise Beetles have a type of shield (hence, their name), but it is formed from expanded, hardened forewings, and is not a fecal shield. The larvae of these beetles have fecal shields which serve as chemical deterrents, preventing most predators from even touching them. The deterrent in the feces comes from the beetles’ food source — plants in the order Solanales. Tortoise Beetle larvae have what is known as a “fecal fork” on their last abdominal segment, which they hold over their body. The larvae maneuvers its muscular, telescopic anus, or “anal turret” in such a manner as to excrete its feces and bits of shed exoskeleton onto the fecal fork, forming an umbrella-like fecal shield.

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Beaver-Porcupine Encounter

beaver with quills2  376A Porcupine’s 30,000 quills effectively defend it against two and four-legged enemies, and occasionally against its own species. Rarely, however, do we see evidence of this mode of defense outside of our family dogs, most of whom are challenged when it comes to learning from the experience. From the size of the quills in this Beaver, one can assume it came in contact with either the Porcupine’s upper back or neck, where the quills are longest (up to 4”). How and where this encounter took place is a mystery. Porcupines can and do swim – their quills are filled with a spongy material which may enhance their buoyancy. So it’s within the realm of possibility that these two rodents met in the water, but that seems unlikely. While some quill injuries result in death, a surprising number of victims recover. One researcher observed that the quills he saw in a raccoon’s muzzle were worn down to a stubble within a week. Due to tiny barbs on the end of the quill that contacts another animal, it can work itself into an animal’s body, but those in this Beaver will hopefully come to rest against its jawbones. As long as the Beaver can eat, its chances of survival are good. It is unlikely to get an infection from the quills, as they’re coated with fatty acids that inhibit the growth of bacteria (in case the Porcupine stabs itself?)

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Snowshoe Hares

1-21-14 snowshoe hare by Patsy Fortney IMG_4140 (3)You’re most likely to see Snowshoe Hares at dawn or dusk, when they are most active. That is, if you can detect them before they detect you. Snowshoe Hares depend upon camouflage as their first line of defense, with seasonal coats to match their environment. They sometimes freeze where they are, making no movement, or take shelter in a protected spot or “form” and sit quietly, with their feet tucked out of sight and their ears pressed tightly against their back, making them all but invisible. If threatened, they can break into a full run leaping up to 12 feet at a time, reaching 30 or more miles per hour thanks to their powerful hind legs. (Photo by Patsy Fortney)

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Eastern Chipmunks “Clucking”

10-2-13 eastern chipmunkIMG_3035Especially in the fall, and sometimes in the spring, the woods are full of “clucking” Eastern Chipmunks. It’s unusual to hear this call during the summer, but once leaves have started to fall off the trees, giving chipmunks a clearer view of the sky, the chorus begins. One chipmunk starts calling, and the message is passed on to other relatives, who join in. These vocal little rodents are warning each other of the presence of an aerial predator, perhaps a hawk or day-hunting owl. The next time you hear this distinctive alarm call, look skyward. You may well be rewarded with the sight of a raptor flying overhead.

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Green Lacewing Larvae Use Corpses as Camouflage

9-19-13 lacewing larva  232Green lacewings are aptly named for the prominent venation of the adults’ wings. Some species in this insect family even have “ears” in the larger veins that allow them to detect the ultrasonic sounds made by hunting bats. Lacewing larvae and adults are both predators of soft-bodied insects such as aphids. Larval lacewings have long, hollow mandibles with which they puncture prey and suck out the liquefied contents, leaving the woolly husks. Some species of lacewing larvae have hairy backs, and camouflage themselves when in the presence of woolly aphids by sticking aphid husks on these hairs. These “trash packets” camouflage the lacewing larvae from predators, including ants that would otherwise attack the larvae if they recognized that they were lacewings and not woolly aphids.

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Woodland Jumping Mouse Succumbs

8-13-13  woodland jumping mouse134Usually animals that have been killed don’t last long enough for humans to discover them unless the human disturbs the predator right after it’s killed its prey. This may well have been the case when I came upon this Woodland Jumping Mouse. It is actually fairly unusual to set eyes on a jumping mouse, dead or alive, as they are quite secretive. This remarkable one-ounce rodent has long hind feet and a distinctly long tail, which makes up more than half of its total length of eight to ten inches. Using its hind limbs for propulsion and its tail for balance, the Woodland Jumping Mouse is able to make large leaps of up to eight feet or more to escape danger. (More often it walks around on all fours, or uses short hops for greater speed.) Another survival strategy that jumping mice use is to remain motionless for up to several hours, relying on their coloration and cover for protection. Apparently neither adaptive behavior was effective enough to spare this mouse’s life.

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Abbott’s Sphinx Moth Larva

7-26-13  Abbott's Sphinx Moth larva 066Abbott’s Sphinx Moth larvae feed on grape and Virginia creeper leaves during the night. During the day they tend to rest on the woody vines of the plants they are eating, and because they are well camouflaged, they remain hidden from most humans’ eyes. Both as larvae and adults, these moths are well equipped for survival. Older larvae have two color forms, one resembling unripe green grapes (in photo), and the other is brown and looks much like a branch. In their last stage, or instar, both forms have a rear eyespot which looks like a human eye, right down to the white reflection spot in it, which scares off potential predators. If the caterpillar is pinched or prodded, it squeaks and tries to bite the attacker. The adult moths, which emerge next summer after pupating all winter, also defend themselves with both color and behavior. They are brown with yellow bands on their underwings, which make them look something like a bumblebee, and when they fly, they create a buzzing noise. (Thanks to Heidi, Tom and Simmy Wetmore for photo op.)


Caterpillar Survival Strategies

6-14-13 camouflaged catterpillar 049The larvae of moths and butterflies are very susceptible to predation, especially by birds, and they utilize many different strategies to protect themselves. Shapes, colors and behavior all contribute to their survival. Some larvae take on the appearance of less appetizing things, such as bird droppings, twigs or leaves. Some have large eye spots which presumably scare predators. Others have cryptic coloration which makes them all but invisible. The pictured green caterpillar uses both color and behavior to visually disappear on the fern it is consuming.


Killdeer Distracts Predator by Feigning Injury

4-15-13 killdeer IMG_8336

Killdeer arrived back in northern New England last month and have already begun nesting. Being a ground nester, the killdeer has many mammalian predators from which it needs to protect its eggs, including weasels, skunks, opossums and raccoons. Nesting killdeer have a number of responses to predators, which include several different types of distraction displays which draw attention to the bird away from its nest. One of the most common displays is to feign injury by assuming a position which makes the bird appear vulnerable. When a predator approaches, the bird runs away from the nest, crouches with its head low, wings drooping and tail fanned and dragging the ground to display its rufous rump-patch. The predator typically follows, seeing an easy meal, and as soon as it gets too close for the killdeer’s comfort, the killdeer continues to lead it off by alternate flights and sprints.


Shrew Defense Mechanism

3-8-13 coyote digging up shrewIMG_5320Coyote tracks led to a hole dug in the snow, with the body of a shrew lying on top of the snow next to the hole. Apparently a coyote had succeeded in catching the prey it had heard, but upon smelling this tiny insectivore, the coyote decided it wasn’t that hungry. In addition to having poisonous saliva that immobilizes small prey, shrews possess two glands on their sides that emit an unpleasant odor, detectable even by human noses. Although this odor did discourage the coyote from eating the shrew, it wasn’t enough to save its life.


A Great Christmas Present!

If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill.  A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!

One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”

In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e  book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”

I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!


Camel Crickets

Camel crickets are named for their humpback appearance. We don’t often see these wingless insects, for they prefer dark, damp habitats such as under stones and logs, where we don’t often look. However, when there are extreme weather conditions, such as excessive rainfall or the extended periods of hot, dry weather which we have experienced this summer, camel crickets are attracted to damp cellars and crawl spaces, giving us an opportunity to admire their impressive legs. Often mistaken for spiders, camel crickets do have long legs, but only six, not eight, of them. Their two hind legs are obviously longer and stronger than the other four, and enable this cricket to jump three feet high, a skill they use for defense against predators. A local blog reader reports that three nights in a row (camel crickets are nocturnal), due to the force of its jump, a camel cricket tripped a small have-a-heart trap set in their cellar for mice. (Thanks to the Choukas for photo op.)


Giant Swallowtail Caterpillar Defenses

The Giant Swallowtail (Papilio crestphones) appears to be extending its range northward into Vermont.  It was first confirmed here two years ago, and more sightings have been made each summer since then.  The Giant Swallowtail is the largest butterfly in North America, with roughly a 4-6-inch wingspan. Because of the caterpillar’s preference for plants in the citrus family, this butterfly is generally is found further south.  However,  Prickly Ash (Zanthoxylum americanum) is found in northern New England, and it is a member of the citrus family.  With this food source, and increasingly warm winters, the Giant Swallowtail may be here to stay.  The larval stage, or caterpillar, is as, or more, impressive as the adult butterfly.  Its defense mechanisms have to be seen to be believed.  The caterpillar looks exactly like a bird dropping (it even appears shiny and wet), making it appear unpalatable to most insect-eaters.   As if that weren’t enough, when and if it is threatened, a bright red, forked structure called an osmeterium emerges from its “forehead” and a very distinctive and apparently repelling odor to insect-eaters, is emitted.


Hickory Tussock Moth

 

Most tussock moths, such as this Hickory Tussock Moth (Lophocampa caryae), are densely covered with hair-like structures called setae that bear microscopic barbs.  Many people are sensitive to these setae and get an itchy rash if they handle a Hickory Tussock Moth.   Even touching the cocoon of a tussock moth can cause irritation, as the setae are woven into it.  Many tussock moths display warning coloration with their black, white, red, orange or yellow setae.  What looks like two Hickory Tussock Moth larvae in the photograph is actually one adult caterpillar (left) and its shed skin (right).   You can find these larvae feeding on hickory, walnut, ash, oak and many other trees in the woods right now.  After spending the winter pupating in a cocoon in the leaf litter, a small spotted, tan moth emerges.


Earwigs

People used to believe that earwigs crawled into people’s ears while they were sleeping and proceeded to bore into their brains, thereby causing insanity and/or death. Fortunately, this isn’t, and never has been, true. Earwigs feed on leaves, flowers, fruits, mold and insects, but not human brains. Because they are nocturnal, during the day we often find them secreted away in some dark, damp crevice, often on a plant. These flat, elongated insects have a pair of pincers, or cerci, at the end of their abdomen which they use to capture prey, defend themselves and arrange their hind wings, if they have them. (Earwigs that possess wings can, but rarely do, fly.) You can actually determine the sex of an earwig, should you be so inclined, by the shape of its cerci – those of a male (pictured) are unequal in length, strongly curved and larger than the straight cerci of females.


Viceroy Butterfly

The Viceroy Butterfly closely resembles the Monarch Butterfly, but is smaller, and has a black line that runs across the veins of its back wings, which the Monarch lacks. While Viceroys don’t contain the poisonous cardiac glycosides that Monarchs do, they do contain salicylic acid due to fact that the larvae feed on willows. This acid not only causes the Viceroy to taste bad, but makes whatever eats it sick. So not only do these two butterflies look alike, but they discourage predators in the same way. This is not a coincidence. The fact that they are both toxic if eaten and are preyed upon by some of the same predators has led to their similar appearance. This phenomenon is referred to as Müllerian mimicry, and essentially it means if two insects resemble each other, they both benefit from each other’s defense mechanism — should a predator eat one insect with a certain coloration and find it inedible, it will learn to avoid catching any insects with similar coloration.