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Defense Mechanisms

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.)


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